Contents lists available at ScienceDirect

Geoderma

journal homepage: www.elsevier.com/locate/geoderma

Organic matter in the agricultural soils of Tasmania, Australia – A review

William Edward CotchingTasmanian Institute of Agriculture, University of Tasmania, PO Box 3523, Burnie, TAS 7320, Australia.

A R T I C L E I N F O

Editor: I. Kögel-Knabner

Keywords:Organic carbonHumusBiocharDynamicCrop yield

A B S T R A C T

A review of both the living and non-living components of soil organic matter (SOM) in the agricultural soils ofTasmania, Australia, and the relationship of SOM to the functions of soil has been undertaken. The relationshipsbetween soil organic carbon (SOC) and other inherent and dynamic soil properties of Tasmanian soils, SOCstocks, the components and the controlling factors are reviewed. The dynamic nature of SOM is reviewed astargets, rates of change and trends on different soil orders and under different management as well as thecorrelation to soil physical, chemical and biological properties. Information on macro fauna, meso fauna, fungiand bacteria is considered to acknowledge that SOM is a dynamic, changing resource that reflects the balancebetween the living components that add new organic matter and the loss of organic matter from the deadcomponent.

1. Introduction

Soil organic matter (SOM) consists of living organisms, slightly al-tered plant and animal residues, and well decomposed organic residues(Magdoff, 1992). SOM is a reservoir of plant nutrients in soils, and isimportant in maintaining soil tilth, aiding infiltration of air and water,promoting water retention, reducing erosion and controlling the effi-cacy and fate of applied pesticides (Sikora and Stott, 1996). Its darkpigmentation also assists in the absorption of heat, thus acting as a heatreservoir. An understanding of organisms in soil and soil biology ishighly relevant to maintaining or increasing yields and reducing lossesfrom soil borne diseases in Australian cereal and pasture production(Martin, 1993). SOM is a dynamic, changing resource that reflects thebalance between addition of new organic matter and loss of organicmatter already in the soil that is in part controlled by the living bio-logical activity. The potential effects of SOM on the productive capacityof soils are of practical and economic importance to famers and otherswho have an interest in land management. Soil organic carbon (SOC) asa measure of SOM, is widely considered an important measure of soilquality because of the role SOM plays in soil physical, chemical andbiological processes (Doran and Parkin, 1994; Gregorich et al., 1994;Baldock and Skjemstad, 1999). Changes in SOM status have been as-sociated with an improvement or deterioration in the behaviour ofagricultural soils (Loveland et al., 2001).

When soils are sampled and the organic matter analysed, both theliving and non-living components are incorporated. There is a body ofresearch on the methods of analysis and the characteristics, stabilisationand turnover times of the non-living SOM (Baldock and Nelson, 2000;

Lützow et al., 2006) and a seemingly separate body of research on theliving soil biology that includes both the macro-fauna and microbiology(Paul, 2014; De Deyn et al., 2003). The objective of this review of boththe living and non-living components of SOM is to describe what are theamounts and distribution of SOM in Tasmanian soils, the inherentfactors controlling SOM, and also to quantify how dynamic it is andwhat influences these differences. This review acknowledges that SOMis a dynamic, changing resource that reflects the balance between theliving components that add new organic matter and the loss of organicmatter from the dead component. This review is probably only feasiblebecause of the limited geographic extent of the study area, Tasmania,an island state of Australia that is located 240 km south of the Aus-tralian mainland (42°S 147°E) and covers 68,400 km2. It has a cooltemperate climate and contains a diverse range of soils due to variationsin climate, landscape and geology with all of the 13 Australian soilorders represented (Cotching et al., 2009; Isbell, 2002). Tasmania is anexample of a cool temperate climate in which agriculture operates on arange of soil types.

2. Methods

This review considers published manuscripts, contract reports anduniversity theses on what is known about SOM in Tasmanian soils andplaces the knowledge in a broader Australian context. The relationshipsbetween SOC and other inherent and dynamic soil properties, targetsand trends for Tasmanian soils, what role amendments play and alsoliving soil biology components are canvassed. Soil biology is potentiallythe most dynamic component of SOM that includes earthworms and

http://dx.doi.org/10.1016/j.geoderma.2017.10.006Received 24 July 2017; Received in revised form 5 October 2017; Accepted 6 October 2017

E-mail address: Bill.Cotching@utas.edu.au.

Geoderma 312 (2018) 170–182

0016-7061/ © 2017 Elsevier B.V. All rights reserved.

MARK

other soil macro-fauna, meso-fauna such as mites, arthropods and ne-matodes, and micro-fauna including fungi and bacteria. The ecosystemfunction of the different organisms is not reported here, but rather theirdynamic nature and diversity. Suggestions are made about managementpractices, knowledge gaps and potential future areas of research.

3. Results

3.1. Carbon stocks and distribution

Tasmanian soils have C stocks of 49–117 MgC ha−1 in the upper0.3 m as reported by Cotching (2012). Ferrosols had the largest soil Cstocks (117 MgC ha−1) and are a significant soil order (8.4% of landarea) occurring throughout Tasmania (Cotching et al., 2009). Carbonstock to 1 m depth of 117 MgC ha−1 was measured in an apple orchardin southern Tasmania (Gentile et al., 2016a). Cotching et al. (2013)reported that Ferrosols had 139 MgC ha−1 with 150 Mg ha−1 underpasture and 125 Mg ha−1 under cropping but stocks as great as285 MgC ha−1 have been reported from Red Ferrosols under perennialpasture (Cotching, 2009). The amounts of organic matter in Ferrosolsincreases with distance from the coast as both rainfall and elevationincrease (Loveday and Farquhar, 1958). High organic matter content inFerrosols mapped as “snuffy” soils that are hard to wet and erodible,has been found to be associated with very old pastures that have had norecent history of cropping or pasture renovation (Eldridge, 2000). Thehigh SOC stocks are likely to be in part due to the dominance of poorlycrystalline iron (Fe) and aluminium (Al) oxides and hydroxides inFerrosols, as these minerals have a larger surface area for SOC sorptionthan do crystalline minerals such as goethite and hematite Fe oxides, orsilicate clays.

Dermosols, which are the dominant soil order in Tasmania (24%),with predominantly clay loam surface textures and rainfall > 1000mm/year, also had high soil C stocks. Cotching et al. (2009) reported103 MgC ha−1 with 102 MgC ha−1 under pasture and 83 MgC ha−1

under cropping at 0–0.3 m depth (Cotching et al., 2013). Organosolsdid not have the largest soil C stocks in Tasmania, due to the low bulkdensity (BD) in organic rich materials of 0.17–0.25 Mg m−3 in thesurface 0.3 m. Also, many of the Organosols in Tasmania are shallow,ranging from 0.2–0.4 m in thickness, and overlie a range of substratesfrom massive quartzite to gravels. Chromosols, Kurosols, Sodosols, andTenosols had lower soil C stocks of 69–78 MgC ha−1 due to their sandysurface textures. Doyle (2013) reported texture contrast soils to have65 MgC ha−1 under pasture and 58 MgC ha−1 at 0–0.3 m depth undercropping. Hydrosols and Podosols, both of which have wet hydrologicregimes in Tasmania, had relatively large soil C stocks (116 and98 MgC ha−1, respectively), as these soils have high C inputs underhigh rainfall and long periods of saturation, which result in accumu-lation rather than oxidation of organic matter. Vertosols were reportedas having 107 MgC ha−1 under pasture and 96 MgC ha−1 under crop-ping (Doyle, 2013). The range in carbon stocks at 0–0.3 m depth inTasmanian soils (49–285 MgC ha-1) is greater than the2–239 MgC ha−1 reported in Victorian soils (Robertson et al., 2016).Organic carbon stocks in Tasmanian soils at both 0–0.3 and 0–1.0 mdepths are significantly greater than those in other eastern Australianstates (Table 1). The increase in soil C stocks from Queensland toTasmania is likely to be the result of decreasing mean annual tem-perature and increasing annual precipitation from north to south,which results in greater production and less oxidation of organic matterand so greater accumulation under cooler temperatures (Baldock andSkjemstad, 1999).

Measuring carbon as a stock in MgC ha−1 can mask the true carbonstory as land use affects soil bulk density. The carbon stocks as mea-sured in the 0–0.3 m depth can be significantly influenced by com-paction causing increased bulk density of the soil (Ellert and Bettany,1995). Also, any simple or quick field assessment of soil carbon will behampered by the need to take adequate BD measurements needed to

calculate stocks. Carbon stock figures are quite different to the TOCfigures due to differences in bulk density between land uses being dif-ferent for different soil orders. Ferrosols were found to have littlechange in stock between pasture and cropping compared to the changein TOC (33% compared with 35%). This indicates that the Ferrosols donot increase in bulk density with cropping to the same degree as Ver-tosols which had a greater difference between TOC and stock percen-tage changes with land use (36% for TOC compared with 20% forcarbon stock) (Doyle, 2013).

The range in C stock values within soil orders indicates that therewould be considerable uncertainty if an assumed baseline value for anyparticular soil order were to be used for soil carbon accounting. Thus, itis critical to determine initial soil C stocks at individual sites and farmsfor C accounting and trading purposes, because the initial soil C contentwill determine whether there is potential for current or changed man-agement practices to result in soil C sequestration or emission. Thecalculated carbon storage in the upper 0.3 m of soils for individualfarms was found to vary depending on the data used and the scale ofinvestigation. Broad scale assessment using the on-line Australian soilresource information system (ASRIS) information ranged from being16–83% less than that determined from farm scale information(Table 2; Cotching, 2009). The differences are similar or much greaterthan those found by Frogbrook et al. (2009) who found differences of8% and 45% for areas in Scotland and Wales respectively when com-paring field survey data with information from the national UK data-base. The differences in the Tasmanian study are likely to be due to a

Table 1Profile soil carbon stocks in Australian soil orders by State (Cotching, 2012).

Soil order State Soil Ca 0–0.3 m Soil C 0–1.0 m

Mg ha−1 se Mg ha−1 seChromosol Queensland 49.4 0.9 147.2 8.3

NSW 46.4 4.3 97.3 12.7Victoria 36.9 nd 88.8 ndTasmania 75.6 10.9 105.0 13.2

Dermosol Queensland 42.9 nd 77.1 ndNSW 110.8 9.1 175.6 14.3Tasmania 124.0 21.8 228.2 31.8

Ferrosol Queensland 34.0 1.1 60.0 0.7NSW 133.9 8.1 228.3 17.2Tasmania 122.7 16.3 212.2 29.2

Hydrosol NSW 72.3 14.8 112.3 8.2Tasmania 129.6 27.9 235.4 45.2

Kandosol NSW 86.9 4.6 132.0 6.1Kurosol NSW 50.4 19.6 85.2 22.5

Tasmania 71.0 8.9 136.7 11.3Podosol Tasmania 82.2 18.8 163.4 24.8Sodosol Queensland 43.3 3.4 81.1 5.2

NSW 50.5 4.5 76.7 6.9Victoria 26.8 1.9 49.1 4.7Tasmania 77.2 7.2 129.0 10.6

Tenosol NSW 69.5 7.1 98.6 13.1Vertosol Queensland 40.3 1.0 97.2 4.0

NSW 37.3 1.3 74.5 3.7Tasmania 171.2 nd 327.5 nd

a LECO carbon (Rayment and Higginson, 1992).

Table 2Soil carbon stocks mapped at different scales in Tasmania (Cotching, 2009).

Farm area(ha)

No. ASRISa

map unitsASRIS soilcarbon(MgC)

No. farmscalemap units

Farm scale soilcarbon(MgC)

Farm A 460 1 39,117 8 46,446Farm B 753 2 13,777 14 82,446Farm C 305 2 38,997 17 58,212

a Australian Soil Resource Information System available at: http://www.asris.csiro.au/.

W.E. Cotching Geoderma 312 (2018) 170–182

171

number of factors including: soils mapped at the farm scale are notincluded as components in the broad scale information; and attributeddepth, soil carbon and bulk density values in the ASRIS data are derivedfrom similarly mapped land system polygons, that are not re-presentative of the soil attributes that were measured on these specificfarms. The discrepancies in this study are disturbingly large and in-dicate that the use of broad scale information within ASRIS, which isthe Australian national database, can lead to large errors in calculatingon-farm soil carbon storage. Individual sites require the establishmentof their own baseline data with ongoing monitoring over time. TheFarm Carbon Story adopted in Tasmania (Cotching, 2009) uses in-formation that is already routinely compiled as part of a well deliveredproperty management plan such as a farm map, soil types and land useareas, as the basis for summarising the overall carbon picture of thefarm. It is designed to present the farmer with the big picture of carbonstores and fluxes on their farm rather than just their emissions andsequestrations which are the focus of current carbon accounting usingexisting carbon calculators.

The largest concentrations of soil carbon are generally found in theuppermost layers of the soil since this is where the bulk of organic in-puts occur. The SOC appears to be relatively uniformly distributedthrough the upper 0.3 m in Tasmania, with approximately half (0.56) inthe upper 0.15 m across all soil orders (Cotching, 2012). However, thisdisguises the range in values of the proportion in the upper 0.15 m. Thetexture-contrast Sodosols had the largest range in proportion of soil C inthe upper 0.15 m (0.34–0.80) and uniform-textured Vertosols had thesmallest range (0.44–0.65). Other orders had ranges of 0.33–0.74. Thevariability in these results indicates that the magnitude of changes inSOC at the different depths differs between soil orders (Baldock andSkjemstad, 1999) and that there is considerable variability within anyparticular soil order. Variability with respect to where the SOC occursin the upper 0.3 m is likely to be due to many factors including tillageand associated depth of turnover of soil layers, compaction resulting indifferences in bulk density, previous crop types and associated rootdistribution, bioturbation by soil invertebrates and tree turnover, andsoil erosion/accumulation. Tasmanian soils had an average 1.87 times(range 1.27–2.46) the C stock in 1.0 m of soil as in the upper 0.3 m(Table 3; Cotching, 2012), demonstrating that current soil C measure-ment protocols ignore deeper portions that might also respond tomanagement (Syswerda et al., 2011). If a change in soil C deeper in theprofile occurs, this might affect how SOC can be managed for seques-tration. The levels of OC below 0.3 m depth in Tasmanian soils, indicatethat generalised conclusions about SOC in Australian soils must bequalified as SOC effects will influence soil physical properties beyondthe top 0.1 m of soil and are not minimised by 0.2 m depth (Murphy,2015).

Increasing SOC levels at 0.1–0.3 m depth were found to be asso-ciated with increasing intensity of land use on Dermosols, but this didnot offset losses in the top 0.1 m of Dermosols (Scandrett et al., 2010).There are significant differences between land uses with soils underagriculture having a greater proportion of the total soil carbon in theupper 0.3 m of profiles to 1.0 m depth than soils under forestry(Table 3). Tasmanian agricultural soils had a mean proportion of 0.66of profile soil C in the upper 0.3 m and forest soils had a mean pro-portion of 0.51 (Cotching, 2012). Podosols had both the smallest andlargest multipliers, illustrating the variability within any given soilorder. The proportional decrease in SOC with depth was found to begreater under pasture than under cropping in all soil orders with thegreatest proportional differences occurring on texture contrast soilsunder pasture (Cotching et al., 2013), that is likely to be due to de-creasing clay content with depth associated with the presence of asandier A2 horizon in texture contrast soils (Doyle, 1993). SOC was50% less at 0.1–0.2 m than at 0–0.1 m depth under pasture and 37%less under cropping on texture contrast soils. Ferrosols had the leastproportional decrease in SOC with depth as SOC at 0.1–0.2 m was 28%less than at 0–0.1 m depth under pasture and 9% less under cropping(Cotching et al., 2013). Ferrosols have been intensively cropped for>50 years in Tasmania making them some of the most intensively mixedsoils in Australia (Cotching, 1995). The long cropping history andregular mixing to depths between 0.2 and 0.3 m depth for potatoes andother root vegetable crops probably account for Ferrosols exhibiting theleast proportional difference in SOC between 0 and 0.1 and 0.1–0.2 mdepth of the soil orders sampled.

There were no significant differences in soil organic carbon(0–0.3 m depth) between a chronosequence of 21 forest restorationplantings aged from 6 to 34 years old, remnant forest and pasture inTasmania's Midlands with all values in the range of 59–67 Mg ha−1

even with biomass carbon accumulation during the first 34 years afterplanting of 4.2 ± 0.6 MgC ha−1 year−1 (Prior et al., 2015). This is inline with other studies that show soil carbon is slow to respond tochanges in land use. Such slow changes over long time frames i.e.>300 years, has also been reported for decreases in SOC when primaryforest is logged and then subjected to harvesting cycles (Dean et al.,2017). The drop on SOC is driven by the biomass drop from the primaryforest level but takes time to adjust to the biomass equilibrium.

3.2. Factors that control soil organic carbon

The strongest influences on soil organic carbon concentration inTasmania were found to be inherent site factors of soil order and meanannual rainfall with potentially dynamic land use also being a moredominant influence than the dynamic soil management variables pro-vided by farmers from their 10 year paddock histories (Cotching et al.,2013). This included the number of crops grown and the type andamount of tillage practiced. There was a trend for conventional tillageto be associated with lower TOC than with no or minimum tillage butthe results were not significant (P < 0.05). The influence of soil depthdecreased in a similar manner so that TOC was influenced at all depthsin all soil orders by mean annual rainfall but soil management had agreater influence closer to the soil surface. There were no associationsbetween TOC and other dynamic soil management variables includinggrazing management, number of long fallows, type of crop grown, orrates and types of fertilisers applied. The following hierarchy of influ-ence of variables on SOC was proposed by Cotching et al. (2013):

Soil order > mean annual rainfall > land use > cropping fre-quency > tillage type.

This general hierarchy of influence on SOC is different to that re-ported by Robertson et al. (2016) for Victorian soils of: climate > soilproperties > management class > management practices. The dif-ference in hierarchy reported for Tasmania (413–1352 mean annualrainfall) and Victoria may be due to the greater climate gradient of sitessampled in Victoria (249–1849 mean annual rainfall) as within

Table 3Profile soil carbon stocks (MgC ha−1) in Tasmanian soils under different land uses(Cotching, 2012).

Soil order Land use 0–0.3 m 0–1.0 m

Mean se Mean seChromosol Forestry 68 9.7 94 11.8Dermosol Agriculture 91 9.6 128 14.1Dermosol Forestry 123 31.2 252 39.6Ferrosol Agriculture 148 13.9 230 31.6Ferrosol Forestry 88 16.6 166 35.3Hydrosol Agriculture 84 7.4 148 27Hydrosol Forestry 148 40 273 35.6Kurosol Agriculture 78 nd 104 ndKurosol Forestry 60 9.1 127 11.6Podosol Agriculture 116 nd 148 ndPodosol Forestry 59 13.1 145 31.3Sodosol Agriculture 66 7.7 112 13.7Vertosol Agriculture 153 nd 292 nd

Walkely-Black carbon (Rayment and Higginson, 1992) n.d., not determned.

W.E. Cotching Geoderma 312 (2018) 170–182

172

individual Victorian regions, the apparent influence of climate and soilproperties on SOC stock varied, and in some regions, much of thevariation in SOC stock remained unexplained.

Rainfall varies considerably around Tasmania and higher SOC levelshave been reported in the higher rainfall areas of Devonport, Burnie,North East and Deloraine (942–982 mm mean annual rainfall), whilstthe drier regions of Brighton, Derwent Valley, Clarence (494–614 mmmean annual rainfall) have lower SOC values (Doyle, 2013). The stronginfluence of climate, in particular rainfall, on soil carbon is demon-strated for one soil order (Dermosols) and under one land use (per-ennial pasture) with a correlation between soil carbon stock and meanannual rainfall of r = 0.56 (Fig. 1).

The relationship between SOC and the inherent properties of thepercentage of silt + clay in Tasmanian soils used for cropping wasfound to mostly follow a previously published linear relationship(Sparrow et al., 2006; Hassink, 1997) which is considered an indicationof the capacity of soils to store C. Soils that showed a major positivedeparture from the relationship were clay loams with> 60% silt+ clay (Ferrosols) under perennial pasture. This may be due to theextra C capacity provided by the high proportion of fine particles inthese soils and the high C inputs from perennial pastures in a cool-temperate climate. Tasmanian Ferrosols appear to have a large capacityto store C in the fine fraction, but they also appear to be able to readilylose C from this fraction. When compared with Ferrosols under pasture,most of the cropped Ferrosols had C storage close to Hassink's re-lationship. In the absence of the C inputs that pastures provide, andwith the influence of fallow periods and tillage, C in the fine fractiondecreases (Sparrow et al., 2006).

A negative correlation between land slope (an inherent factor) andsoil carbon content was found on Red Ferrosols (Cotching et al., 2002c).Soil carbon content was significantly lower (P < 0.001) on slopes of13–18% and 19–28% compared to level or accumulating sites whichwas attributed to erosion on the steeper slopes. Steeper slopes(19–28%) had more variable carbon contents (2.1–4.7%) than less steepslopes and this variability was attributed to non-uniform effects of rillerosion that removes furrows of organic rich topsoil whilst leavinginter-rill areas unaffected.

The implications of the Tasmanian hierarchy of influence are thatpotential SOC is determined by inherent soil characteristics of claycontent and clay type that are encapsulated by soil order, and so theamount of SOC stored in soil tends to increase with increasing claycontent. The attainable level of SOC is determined by the local climate,an inherent factor, predominantly annual rainfall. Actual SOC is de-termined by the dynamic factors of type of land use and the soil man-agement practices undertaken including fertiliser additions that con-tribute nutrients other than carbon to SOM (Fig. 2). Although it is notpossible to increase the attainable SOC in soil, management practicesdetermine whether or not the dynamic attainable storage of SOC in soilis achieved. Farmers can influence SOC more by their choice of land use

than their day to day soil management but even although the influenceof management is not as great as other site inherent variables, farmersare still able to select practices that retain more SOC than others.Farmers can crop less frequently and reduce the amount of tillageduring soil working as long as these practices are considered togetherwith economic sustainability.

The effects of different farm management practices on soil carbonwere assessed using Black Magic (Leigh Sparrow pers. comm.) which isa model adapted from “Roth-C”, a computer model of soil organiccarbon change under UK field cropping (Jenkinson, 1990) to suit Tas-manian soils, climate and crops. The rate constant for the resistant plantmaterial (RPM) pool was adjusted from 0.3 to 0.15 yr−1 as suggestedby Skjemstad et al. (2004). BlackMagic calculates the input of organicmatter from 28 individual crops commonly grown in Tasmanian crop-ping rotations and determines the rate at which organic carbon is oxi-dised and lost from the soil for fourteen different soil/area combina-tions. The total farm carbon stores at 0–0.3 m depth are much larger(i.e. 1000 x greater) than modelled annual emissions or sequestrations(Cotching, 2009). The modelled sequestration of carbon under currentmanagement from measured soil carbon values ranged from 0.13 T CO2

(35 kgC) ha−1 yr−1 under cropping on Sodosols to 1.03 T CO2

(281 kgC) ha−1 yr−1 under perennial pasture on Kurosols. However,the difference between emissions and sequestration is critically de-pendent upon the initial SOC value used in the model as this determinesif SOC is above or below the equilibrium value for the site's combina-tion of soil type, rainfall and land use/management. Perennial pastureon a Ferrosol was modelled to sequester carbon at 0.36 T CO2 (98 kgC)ha−1 yr−1 and a change to cropping would emit carbon at 0.12 T CO2

(33 kgC) ha−1 yr−1. The increases in soil carbon contents under cur-rent management were relatively small, are unlikely to be measurableat the paddock scale over the medium term, and should be interpretedas indicating that current management is sustainable over the mediumto long term in terms of soil carbon balance. The apparently small ratesof sequestration on a per hectare basis (48–63 kgC ha−1 yr−1) areuseful in accounting for carbon at the farm scale when multiplied by thearea used for the particular land uses and these may be off set againstemissions generated by usage of fuel, electricity or fertiliser. The farmcarbon study demonstrated that farmers are custodians of a large bankof soil carbon that is dynamic and susceptible to degradation andconversion into CO2 if management is not sustainable.

Tillage was modelled to increase SOM breakdown by increasing theexposure to air and metabolism by micro-organisms. However, theimpact of tillage was not as great as the effect of other managementfactors, such as length of fallow with bare ground and no tillage, andthe type of crops grown, on the amount of organic matter grown andreturned to the soil. An exception to this is where tillage leads to in-creased erosion. One of the outputs from BlackMagic is a relativecomparison of the amount of soil carbon contributed by each cropgrown in a rotation that is dependent on sowing dates and length ofgrowing season but it allows for a visual comparison that farmers canuse in selecting particular crop components to include in a rotation.Research over an 11 year period in the UK found rotations with 25% orless of pasture phase in combination with cereals and potatoes, resultedin a decline in SOC (Philipps, 2001). Sites under arable agriculture havebeen found to reach stable or very slowly changing SOM levels undercontinuous arable cropping regimes (Hatley et al., 2001). Once theseequilibrium levels are reached, modern farming systems do not causefurther decline in SOM level. The traditional pasture–crop rotationsystem in Tasmania fits well into this equilibrium, with the build-up ofSOM in the pasture phase and the subsequent mineralisation of SOMand release of nutrients in the cropping phase. The author's view thatthe most effective management practice to increase SOC is to increasethe proportion of perennial pasture within crop/pasture rotations issupported by work in other Australian regions (Chan et al., 2011; Luoet al., 2010).

Fig. 1. Relationship between soil carbon stock and mean annual rainfall on Dermosolsunder perennial pasture (Doyle, 2013).

W.E. Cotching Geoderma 312 (2018) 170–182

173

3.3. Rates of change in SOC concentration

SOC is dynamic in that it declines after land use changes frompasture to crop, pasture to plantation and native forest to crop (Luoet al., 2010; Guo and Gifford, 2002). Theoretical predictions concludethat SOC will eventually attain a dynamic equilibrium level when SOCgains equal SOC losses, i.e. a steady-state (Post and Kwon, 2000). Theabsolute changes in SOC percentage are relatively small and are diffi-cult to measure at the paddock scale over the medium term. At sitesunder continuous cropping on Ferrosols average SOC in the 0–0.15 mdepth decreased from 3.7% to 3.2% over a 13-year period (Sparrowet al., 2012). For the three sites that remained in pasture the SOC fellfrom 5.1% to an average of 4.8% whilst at sites converted from con-tinuous pasture to intermittent cropping over the 13 years, SOC wasreduced from 5.8% to 4.5%. Sites with the greatest SOC level at thestart were the most dynamic and declined by the greatest amount overtime. There was a highly significant (r2 = 0.82) exponential relation-ship between SOC at 0–0.15 m depth and the number of years each sitehad been cropped during the 38 years 1972–2010 (Fig. 3). It is difficultto maintain SOC levels under a cropping rotation as cropped paddockson Ferrosols with 0–0.15 m depth SOC> 4% carbon tend to losecarbon whilst paddocks with SOC of< 3% tend to gain carbon (Parry-Jones, 2010). This supports the concept that soils have an equilibriumlevel where soil will stabilise under continuous arable cropping rota-tions (Janzen et al., 1997). The equilibrium concentration of SOC at0–0.15 m depth in Tasmanian Ferrosols under continuous croppingappears to be 2.4–2.7% (Walkley-Black method). Cropped Ferrosolswith SOC values between 3% and 4% need to be monitored for anytrend of further degradation.

3.4. Targets and trends

The quantity of SOC present is considered a “master” soil variable(Wilson et al., 2008) as it is an important measure of soil quality be-cause of the role soil organic matter plays in soil physical, chemical and

biological processes (Baldock and Skjemstad, 1999). An important as-pect of monitoring soil quality is setting target values in order to be ableto evaluate results and to report on changes in soil properties over timedue to the effects of management. The soil quality target for a particularsoil is dependent on its inherent capabilities, the intended land use, andthe management goals (Andrews et al., 2004) and this is the approachtaken in Tasmania rather than a value for SOC that is sufficient for thesoil to perform a specific function. The targets are separate for differentsoil orders, different land uses, surface (0–0.075 m) and subsurface(0.075 m thick sampled between 0.075 m and 0.3 m), and mean annualrainfall (Table 4). If a result falls below the target value, then if theresult is not expected, then a management response is required in orderto correct the soil condition. Such a response may include a change inrotation or a change in cultivation technique from conventional tominimum tillage or to include a pasture phase or lengthen the pasturephase. SOC targets for Tasmanian soils are all > 2% at which it is likely

Fig. 2. Conceptual model of the influence of inherent (clay content & type, rainfall) and dynamic (land use) factors that control Tasmanian SOC stocks (rectangle size represent relativevalue; arrows indicate declining values).

Fig. 3. Relationship between Walkley and Black (1934) organic C and cultivation historyon Tasmanian Red Ferrosols for 0–0.15 m depth (y = 4.971e−0.019x R2 = 0.825)(Sparrow et al., 2012).

W.E. Cotching Geoderma 312 (2018) 170–182

174

that there will be sufficient SOM to maintain most functions (Murphy,2015) and this is greater than the 1.5–2.0% threshold described by Lal(2016) as being essential for a range of soil health attributes. A state-wide survey of soils in Tasmania found that the proportion of sitesbelow SOC targets was 32% of intensive cropping sites and 23% ofperennial horticulture sites (Cotching and Kidd, 2010). The assessmentsagainst broad targets provides a snapshot in time but for dynamic soilproperties, such as SOC, monitoring over longer time frames is requiredto indicate if incremental change is occurring. The soil quality mon-itoring program that began in 2004, selected sites that were biased toagricultural land uses, particularly the more intense uses of cropping,horticulture and irrigated pasture. SOC variability was explained betterby soil order (30% and 48%) than land use (24% and 22%) in bothsurface and subsurface samples respectively (Cotching and Kidd, 2010).

Repeated sampling at each of the state-wide sites approximately5 years after initial sampling, has been undertaken and the comparisonof SOC data for Dermosols under cropping indicates that the measureddecrease in topsoil and subsoil OC was significant (P < 0.05) and thiswas associated with a significant increase in bulk density, an increase inpH and a decrease in aggregate stability (Grose, 2015). The significantdecrease in SOC found on Dermosols under pasture has also been re-ported in New Zealand temperate soils (Schipper et al., 2007). This maybe due to the inherent effect of mineral N applied as fertiliser promotingmicrobial C utilization (Mulvaney et al., 2009) or urine depositionleading to SOC solubilisation and priming of soil C mineralisation underpastures (Lambie, 2012). There is considerable uncertainty regardingthe extent to which different grazing practices alter SOC accumulation(Chen et al., 2015; McSherry and Ritchie, 2013) and SOC responses tograzing are complex because grazing influences many aspects of thepastures ecosystem, including plant community structure, soil proper-ties and nutrient cycling, thereby making it difficult to predict the SOCresponses to changes in grazing management (Eyles et al., 2015). Plantroots play a significant role in C sequestration in pasture soils butvariable findings on the effect of grazing on root biomass suggest thatthe effect of grazing on root growth is complex and complicated by arange of factors including soil type, climate, fertilisation and speciescomposition. The effects of climate change on SOC under pasture havealso not been evaluated with changes in atmospheric temperature andCO2 concentration potentially having measurable effects on plantgrowth and microbial decomposition.

The number of Dermosol sites not meeting SOC targets has

increased from eight to 13 over the 5-year sampling interval. Sitesunder cropping that are below target for OC have also been reported onDermosols and Ferrosols (Cotching, 2010). All of these soil monitoringresults are contributing to a consensus of findings that soil condition inTasmania is declining, and the results should be considered as an earlywarning of possible long-term future trends (Commonwealth ofAustralia, 2011; Grose, 2015; Cotching et al., 2002a, 2002b, 2002c,2002d; Sparrow et al., 1999). It could be that some Tasmanian soils willsustain sufficient SOC reserves to maintain good physical conditionprovided that compaction by tractors is minimised (Gradwell andArlidge, 1971). However, the major challenges for the management ofagricultural soils in Tasmania are still those identified by Cotching(1995) of loss by accelerated soil erosion, structural decline due tocompaction and decreased aggregate stability and declining organicmatter content due to oxidation and erosion.

3.5. SOC fractions

SOM is made up of four major fractions – plant residues, particulateorganic carbon, humus carbon and recalcitrant organic carbon orcharcoal and char-like structures. These fractions vary in their chemicalcomposition, stage of decomposition and role in soil functioning andhealth. Three of these four fractions were further defined by Skjemstadet al. (2004), as:

Particulate organic carbon (POC): Pieces of plant debris 0.053–2 mmin size. POC decomposes relatively quickly (years to decades) andprovides an important source of energy for soil microorganisms.

Recalcitrant organic carbon: Organic material resistant to decom-position and, in Australian soils, dominated by charcoal. The charcoal Ccontent is the amount of SOC in the< 53 mm fraction found to exist inthe form of charcoal as assessed by 13C nuclear magnetic resonance(NMR) analysis after exposure to a photo-oxidation process.Recalcitrant organic carbon can take centuries to thousands of years todecompose, and is largely unavailable to microorganisms.

Humus carbon: Calculated as the total SOC minus the particulate andcharcoal fractions. Humus carbon is more resistant to decomposition bysoil microorganisms than POC, and so tends to turn over more slowly(over decades to centuries). It plays a role in all key soil functions, andis particularly important in the provision of nutrients and has beenfound to be active in mineral degradation in Tasmania (Baker, 1973).

The proportions of the different fractions are important because agreater proportion of POC would indicate that a soil is more susceptibleto SOC decline over time than a soil with a greater proportion of humusor recalcitrant carbon. McDonald et al. (2009) reported that soils withthe greatest SOC levels in Tasmania (Hydrosols and Podosols) alsocontained the greatest amount of POC (Fig. 4). The mean fraction ofPOC relative to total SOC ranged from 0.3 on Dermosols to 0.6 onHydrosols/Podosols. Maximum POC fractions were 0.7 on a Ferrosoland 0.9 on a Hydrosol. In a study of 312 Australian soils, Baldock et al.(2013) found a POC fraction mean of 0.19 with a range of 0.006 to0.60. The large proportion of POC on Hydrosols/Podosols is likely to bebecause the soils sampled in these two soil orders were all saturated forseveral months each year, thus slowing or even stopping SOM turnoverand decay and allowing the build-up of POC. Ferrosols had equal pro-portions of POC and humus whereas Chromosols, Dermosols and So-dosols had greater proportions of humus than POC. The proportion ofSOC as POC appeared to be approximately 50:50 up to 5% SOC(straight line section on Fig. 5) but above levels of 5% SOC, the pro-portion of POC increased as indicated by the steepening slope of theline. Baldock et al. (2013) also found that as the SOC content increased,a greater proportional increase in POC content occurred. Thus at thehigher SOC contents, POC represented a greater fraction of SOC than atlower SOC contents. The fraction of SOC as char in Tasmanian soilsranged from a mean of 0.09 on Hydrosols/Podosols to 0.12 on Chro-mosols, Ferrosols and Sodosols, and 0.15 on Dermosols. Baldock et al.(2013) found resistant SOC to have a fraction mean of 0.26 (range

Table 4Targets for soil organic carbon in Tasmania (Cotching and Kidd, 2010).

Soil order Land use categories Deptha Annualrainfall(mm)

Targetvalue orrange(%w/wOC)

CalcarosolsChromosolsKurosolsPodosolsSodosolsTenosols

All Surface > 2Subsurface > 1

DermosolsFerrosolHydrosols

Cropping & horticulture Surface > 800 > 3< 800 > 2

subsurface > 800 > 3< 800 > 1.5

Pastures & forestry Surface+ subsurface

> 800 > 4< 800 > 2

Vertosols All Surface > 4Subsurface > 3

a Surface = 0–0.075 m; subsurface = 0.075 m thick sampled between 0.075 m and0.30 mm.

W.E. Cotching Geoderma 312 (2018) 170–182

175

0.07–0.74).There is some conjecture about the concept of soil humus as

Lehmann and Kleber (2015) argue that SOM consists of a range of or-ganic fragments and microbial products of all sizes at various stages ofdecomposition rather than decomposition being predominantly in themore labile POC fraction. During the decomposition of fresh organicmaterials (remains of plants, animals and microorganisms) approxi-mately 60–80% of the organic C (the labile fraction) reverts to the at-mosphere as CO2. This is a rapid mineralisation process and usuallytakes place within the first year. The remaining proportion undergoesslower oxidation processes and after complex transformations, it eitherturns into macro- or microbial biomass (5–15%) or is stabilised in theform of humic substances (Gonzalez-Perez et al., 2004). Although allplants contain the same general classes of organic compounds such ascellulose, hemicellulose, starches, proteins, lipids and polyphenols, theproportions of each depend on species and maturity, and influence thedegree and rate of decomposition (Martens, 2000). Decomposition ofcrop residues into SOM (humification) not only sequesters carbon butalso substantial amounts of nitrogen, phosphorus and sulfur that mayrequire application of additional nutrients over and above nutrientsrequired for crop growth (Kirkby et al., 2014).

Evidence to support the Lehmann and Kleber (2015) hypothesis thatdecomposition of all sizes of SOM occurs simultaneously rather thanpredominantly in the more labile POC fraction has been provided inTasmania by Parry-Jones (2010) and Belbin (2003) on Red Ferrosols.

They found that there was no significant change between POC andhumus fractions as a percentage of total organic carbon (TOC) as TOCdeclined with increasing years of intensive cropping. This is in contrastto findings on Ferrosols in Victoria where the decrease in macro-C(> 53 μm) was greater than finer carbon when management changedfrom forest to pasture (Carter et al., 2002). These Tasmanian findingsmay reflect the fact that the size of POC in any of these samples wasunknown and the mean size may be closer to 53 μm in some and to2 mm in others, i.e. a 40-fold range. The findings may also be due to thepresence of abundant iron and aluminium oxides in Red Ferrosols withhigh surface area that allows for greater carbon storage than on thedominant clay mineral, kaolinite, that has a low surface area andtherefore a low CEC and carbon storage capacity (Jardine et al., 1989).The location of organic carbon on these surfaces may make it moreprone to attack and oxidation, especially under cultivation where thesoil structure is disturbed (Belbin, 2003).

3.6. Relationships of SOM to other soil attributes

SOC holds a pivotal role in maintaining soil health due to its re-lationship to other soil properties. SOC was significantly correlated toseveral physical, chemical and biological soil properties on a severalsoil orders in Tasmania (Table 5). The strongest relationships were re-ported to be with BD and plastic limit, properties that impact on soilworkability. SOM increases the soil volume (Hudson, 1994) and there isa strong inverse relationship between soil strength and soil volume. Thelower the BD, the more friable a soil tends to be, and so the less thepower requirement for tillage. The greater the plastic limit, the wetter asoil can be worked without causing plastic deformation or smearing andso the less likely compaction will occur. These are both positive on-the-paddock outcomes of greater SOC levels.

Significant relationships with other soil physical properties (struc-ture score, infiltration, mean weight diameter of aggregates and fieldcapacity) indicate that SOC is likely to influence water holding capacityas there is a strong interaction between soil structure, aggregate sta-bility, bulk density and water-holding capacity (Krull et al., 2004).Plant-available water increases by 2–3.5 mm/10 cm soil for each 1.0%increase in SOC over the range of 0.7–3.0% SOC but the increases ap-pear higher for loams and clays than for sandier soils (Murphy, 2015).Increasing SOC also tends to reduce water erosion by improving ag-gregate stability. Significant relationships between SOC and total ex-changeable bases (TEB) on several Tasmanian soil orders demonstratethe influence that SOC has on soil chemistry, as TEB is the sum of theexchangeable cations calcium (Ca2+), magnesium (Mg2+), potassium

Fig. 4. Soil organic matter components in Tasmaniansoil orders. Mean values (%w/w) of organic carbon(OC - Leco), char, particulate organic component(POC) and humus soils (after McDonald et al., 2009).Error bars are 1 standard deviation.

Fig. 5. Particulate and total organic carbon in Tasmanian agricultural soils.(After McDonald et al., 2009)

W.E. Cotching Geoderma 312 (2018) 170–182

176

(K+) and sodium (Na+) and at the field pH is the effective cation ex-change capacity (CEC) or ECEC (Rengasamy and Churchman, 1999).Significant relationships between SOC and CEC have also been reportedon Australian soils by Chan et al. (1992) and Tranter et al. (2007).

A significant relationship between SOC and microbial biomasscarbon is expected as SOC comprises physically degraded and protectedplant components as well as components synthesised by soil microbes(Kallenbach et al., 2016). Significant positive relationships betweenTOC and microbial carbon measured using phospholipid-fatty acidmethyl esters (R= 0.57), and fluorescein diacetate activity (R= 0.43)have also been reported by Pung et al. (2003) in Tasmanian Ferrosols.However, TOC was found not to be related to labile carbon in appleorchard soils and labile carbon contents were strongly correlated withmicrobial activity as measured by dehydrogenase enzyme activity(Gentile et al., 2016b). Plant material is the food source for soil mi-crobes and so if the soil provides fresh supplies of food, then the mi-crobes will flourish. A negative relationship with soil pH may indicatethat in strongly acidic soils, the microbial population is fungi domi-nated with less bacteria and not so active to decompose dead plantmaterial resulting in an increase in POC.

Crop yield is determined by many factors and so it is often difficultto find a direct relationship between SOC and yield. Unless there isbroad range of SOC levels in the same soil type and climatic zone, it canbe difficult to detect any effects of SOC on yield. The approach of re-lating SOC to individual soil properties means that it becomes possibleto identify how and when SOC might influence yield (Murphy, 2015).The relationship between crop yield and soil properties has been in-vestigated in two ways on a range of Tasmanian soils (Cotching et al.,2002c; Cotching et al., 2004): firstly, how crop yields and soil proper-ties vary in different parts of the same paddocks, and secondly, howcrop yields and soil properties vary from paddock to paddock. Resultscomparing different paddocks growing poppies showed no clear re-lationship between soil carbon and yield (Cotching et al., 2004). This isperhaps not surprising because other important factors like water, fer-tiliser, pest and disease management also varied from paddock topaddock. Good management of these factors would tend to even outany differences due to SOC. When yields were measured at a number ofpoints within individual paddocks a stronger but still variable effect ofSOC could be seen. The within-paddock results were also confoundedby the fact that the sample points were affected to varying extent by

previous soil erosion. Nevertheless, in 4 out of 5 cases higher SOC wasassociated with higher yield. The r2 values were low and so althoughthere may be some cause and effect relationship between SOC and cropyield, there was little predictive value in the SOC values. TOC wasfound to be one of the main factors that significantly affected the per-centage of carrots that are marketable together with the proportion ofdiseased or misshapen carrots (Pung et al., 2003). These three variablesexplained 68% of the variability in saleable carrots. Soil attributes thatincluded SOC, explained 72% of the variation in the condition ofwoodland remnants within the agricultural Midlands of Tasmania, withhealthy sites having higher SOC (Davidson et al., 2007). Grazing history(fencing, grazing frequency and intensity) was the primary manage-ment history factor in separating healthy and poor sites, whilst patchsize, fire frequency and wood gathering were secondary, but significant,factors.

3.7. Soil biology

3.7.1. Macro-faunaThe dynamic nature of agricultural practices that result in changes

due to soil disturbance, soil fertility and/or plant species compositionhave been instrumental in reducing native earthworm populations inagricultural areas (Baker et al., 1997). Exotic earthworms representonly 10% of the total 230 species (Blakemore, 2008), which is the samenumber as the 23 exotics in New Zealand (Ara, 2017) and slightly lessthan the 27 native earthworm species recorded in the UK and Ireland(Sherlock, 2012) but they predominate in the agricultural soils ofTasmania. These same changes have been associated with poor treehealth in remnant woodland fragments of eucalypts in agriculturallandscapes in Tasmania (Close et al., 2004). The introduction of theexotic earthworms Aporrectodea caliginosa and A. longa increased pas-ture production by up to 75% and up to 60% for one species in northernTasmania (Temple-Smith et al., 1993). Introducing earthworms topastures has been found to sequester SOC internationally (Don et al.,2008), but evidence is lacking in Tasmania (Eyles et al., 2015). Earth-worms and other macro-fauna are important movers of organic mate-rials into and through soil, especially earthworms with an anecic habit.A. trapezoides was found to be the most widespread species occupying55% of sites, closely followed by A. caliginosa at 52% (Temple-Smithand Kingston, 1990). These two species are also the most widespread in

Table 5Significant (P = 0.05) correlations (r) between soil organic carbon and other soil attributes in Tasmanian soils.

Attribute

Soil order BD Structurescore

Inf FC MWD LL PL WSA Bio C worms pHw TEB

Dermosola −0.82 nd – – – nd 0.89 – 0.9 0.55 – 0.61Ferrosolb −0.81 nd nd 0.7 0.73 0.79 0.78 0.64 0.54 nd −0.62 –Ferrosolc – nd nd 0.47 −0.55 – 0.52 – 0.9 0.59 −0.44 –Ferrosol nd 0.42d nd nd nd nd nd 0.75e nd nd −0.39 –Sodosolf −0.77 nd 0.57 0.41 – 0.65 0.72 0.65 0.78 – – –Tenosolg −0.73 nd – – – nd 0.75 – 0.57 – – 0.57Vertosolh −0.79 nd – 0.59 – 0.94 0.95 – – – −0.87 0.89Multiplei −0.92 nd nd nd nd nd nd nd nd nd nd nd

nd = not determined;BD, bulk density; BioC, microbial biomass carbon; Inf, infiltration; MWD, mean weight diameter of dry soil aggregates; FC, field capacity; LL, liquid limit; PL, plastic limit; WSA, waterstable aggregates; Wms, total worms; pHw, pH water; TEB, total exchangeable bases.

a Cotching et al., 2002a.b Sparrow et al., 1999.c Cotching et al., 2002c.d Cotching et al., 2004.e Pung et al., 2003.f Cotching et al., 2001.g Cotching et al., 2002c.h Cotching et al., 2002d.i Cotching and Kidd, 2010.

W.E. Cotching Geoderma 312 (2018) 170–182

177

New South Wales and Victoria (Mele and Carter, 1999). The numbers ofearthworms are dynamic with total earthworm population densities onpasture sites ranging from 0 to 565 m−2 (Temple-Smith and Kingston,1990) and even up to 918 m−2 Sparrow et al. (1999). Lower numbers(2–126) were reported on cropped sites (Sparrow et al., 1999; Cotchinget al., 2002a; McDonald and Rodgers, 2010) that may be due to greaterdisturbance, lower SOM levels (Table 5) and greater use of fungicides.A. caliginosa has the greatest reported density of any single species at174 m−2 (Garnsey, 1994). Total numbers of earthworms and numbersof beneficial species were significantly correlated with inherent soilproperties of clay content (Temple-Smith and Kingston, 1990) and A.caliginosa was found to be dependent upon the inherent site char-acteristic of rainfall in Tasmania's Midlands with population density,cocoon production and adult development reducing over a rainfallgradient from 600 to 425 mm yr−1. Populations of A. longa do exist inTasmania, but are very poorly distributed and this indicates that thereis potential for wider introduction of this deep burrowing species withinthis environment (Stevenson, 2011).

The species of dung beetle at a particular site is also affected bychanges in land use. The introduced species of dung beetles prefer theopen grassland habitat provided by cow dung on pastures in Tasmania,whereas the native species prefer marsupial dung that is more prevalentin bushland (Stevenson, 2011). There are 10 species of native dungbeetles that are common in Tasmania, the most common being Ontho-phagus australis (Stevenson, 2011). This beetle is one of the few nativespecies that is found in open grazing land. Since 1972, 13 different dungbeetle species have been introduced to Tasmania of which five are nowwell established. These are the summer active beetles Onthophagus bi-nodis, O.taurus, Euoniticellus fulvus, and the winter active Geotrupesspiniger (‘blue bomber’) and Bubas bison. The terrestrial amphipodKeratroides vulgaris (landhopper) that is normally a forest dweller, is themost common large detritivore in high rainfall pastures in Tasmania(Friend and Richardson, 1986).

3.7.2. Meso- and micro-faunaThe levels of meso-fauna in soils is dynamic as paddocks on Red

Ferrosols with greater levels of soil disturbance (vegetable & othercropping) have lower arthropod, and nematode abundance than pasturepaddocks with low levels of soil disturbance (McDonald and Rodgers,2010). Among the free-living nematodes, omnivorous nematodes (ne-matodes that feed on other nematodes, fungi, algae or other soil or-ganisms) were most susceptible to cultivation. Their average populationin cropped soils in Tasmania was nine times lower than in non-croppedpasture soils (Pung et al., 2003). Their populations also take a longertime to recover from disturbance because they have relatively long lifecycles. Populations of plant parasitic nematodes were much greater inpasture soils than in cropped soils, probably because a large biomass ofplant roots is always present in pastures. The number of arthropodOrders present on Ferrosols was positively correlated to their abun-dance (McDonald and Rodgers, 2010). Oribatid mites, Mesostigmataand Collembola were present in every sample collected. There was noclear seasonal trend in abundance of arthropods with populations ableto peak at any time of year.

A significantly greater abundance of mesostigmatid mites at0.2–0.25 m depth was found following application of poultry manureand poppy seed waste to a Sodosols and a Dermosol in the northernMidlands of Tasmania.(Chapman, 2016). The mite population waslikely responding to improved soil porosity created by subsoil manuringthat will also contribute to improved conditions for crop growth.

3.7.3. Micro-floraMicrobial biomass has been found to be significantly and positively

correlated with SOC levels on nearly all soil orders in Tasmania(Table 5). Microbial activity dynamically responds to the level of itsprimary food source, as measured by SOC content. Paddocks withgreater levels of soil disturbance (cropped vs pasture) had lower fungal

to bacterial biomass ratio and other microbiological indicators, such astotal bacteria, total fungi, gram +ve bacteria, gram −ve bacteria andmycorrhizal fungi (McDonald and Rodgers, 2010; Pung et al., 2003).Protozoa were found to have highly variable abundance that may bedue to them being simple organisms that can reproduce very rapidly inresponse to favourable environmental conditions.

The biomass of bacteria was found to have no relationship to theabundance or biomass of other soil organisms. This may be due to thediversity of bacteria and their ability to exploit a wide range of re-sources under almost any conditions. Bacterial populations are verydynamic and can respond extremely quickly to changes in the localenvironment, such as the season, giving rise to highly variable resultsthat appear unpredictable and difficult to interpret. Sites with thepoorest levels of biological activity retained low levels of all soil or-ganism groups and so have the potential to respond to positive changesin management such as reduced tillage, cover crops, green manures andpasture breaks in cropping rotations (McDonald and Rodgers, 2010).

Inherent differences in climate between sites resulted in greateraverage total microbe, bacteria and yeast biomass and lower averagefungi:bacteria and fungi:yeast ratios under both cereals and pasture inwarmer and wetter Ferrosols in the northwest of Tasmania compared tocooler and dryer Kurosols/Sodosols in the northern Midlands (Cotchingand Blaesing, 2008). However, there was considerable variability in thedata both between sites and between seasons that, in association withthe lack of soil physical and chemical data or crop yields as explanatoryvariables, makes it problematic when advising on possible target levelsfor these soil microbial indicators. Findlay (2013) also found that mi-crobial biomass is highly dynamic with levels varying dramaticallybetween different seasons in Tasmania and that microbial communitycomposition is largely determined by food source with distinct soilmicrobial communities reported for co-occurring grass species on anextremely local scale (Osanai et al., 2011, 2013). Application of Acaciagreen waste biochar was found to improve bacterial and fungal abun-dance 3.5 years after application but not archaeal or other eukaryotacommunity components (Abujabhah et al., 2016a). Soil microbial bio-mass reporting for Australian soils is confounded by differences inmethodology and Gonzalez-Quiñones et al. (2011) recommend thatfuture measurements be conducted using a standardised methodology.Further research is also required to better define limits that are soil typeand land use specific, and with appropriate soil collection times foreach agro-ecological region of Australia.

Arbuscular mycorrhiza fungi (AMF) that are beneficial fungi asso-ciated with plant roots were found in significantly greater numbers in aconventionally managed cherry orchard than in an organically man-aged orchard (Mohamed, 2015). This could be due the fungi respondingdynamically to more herbaceous weeds and grass around the cherrytrees in the conventionally managed cherry orchard than in the organicorchard.

3.7.4. Soil borne diseasesTasmanian soils were found to have greater percentages of Take-All

(caused by the fungus Gaeumannomyces graminis) and cereal cyst ne-matode (Heterodera avenae) than all other Australian states, lessRhizoctonia solani (causes bare-patch disease) than all states exceptQueensland, and similar occurrences of root lesion nematodes(Pratylenchus neglectus and P. thornei) to Victoria (Soil Quality Pty Ltd.,2017). The majority of the benchmark sites had levels of diseases andpests that were below detection with a minority of sites having amedium or high occurrence of Take-All (17 and 7% respectively) and amedium or high occurrence of cereal cyst nematode (4 and 5% re-spectively) (Fig. 6). The presence of these pathogens does not ne-cessarily pose a threat to crop production and the impact that thesepathogens have on plants will depend on having a suitable host as wellas a favourable soil environment for the pathogens. This dependencyprovides an opportunity to modify dynamic soil conditions, such asSOM and waterlogging, with different management practices for long-

W.E. Cotching Geoderma 312 (2018) 170–182

178

term control through suppression of soil borne pathogens.Biofumigation crops that act as break crops, disrupting the lifecycle

of pests and diseases, with disease suppression resulting from directbiocidal toxicity as well as indirectly through changes in the soil faunaand the microbial community, offer an opportunity for management ofsoil borne diseases. Brassica green manure plants that produce highconcentrations of biofumigants (Blaesing and Rogers, 2016) were foundto have advantages over non-brassica green manure plants for Scler-otinia wilt disease control in lettuce crops (Pung et al., 2004). Fodderrapes (BQ mulch), which produce high levels of biofumigants in theirroots were more effective for Sclerotinia control than mustards (Brassicajuncea cultivar Fumus), that produce high levels of biofumigants in theirfoliage. Control of the soil-borne potato diseases common scab andpowdery scab, caused by Streptomyces scabiei and Spongospora sub-terranea respectively, and black scurf and Rhizoctonia canker, caused byRhizoctonia solani, using green manure break crops, including biofu-migants and ryegrass, was unsuccessful on a Ferrosol in northwestTasmania (Sparrow, 2015). Changes in plant and environmental con-ditions can affect the release of specific compounds that stimulategermination of Spongospora subterranea resting spores that is the causalagent of powdery scab and root diseases of potato and so selection orbreeding of cultivars that are resistant to soil borne diseases are oneoption to reduce disease incidence (Sparrow and Wilson, 2012; Sparrowet al., 2015; Tegg et al., 2012). Crop growth benefits from growing amustard biofumigant Brassica juncea cultivar Caliente, were incon-clusive (Finnigan, 2013) But one of the advantages of biofumigant cropsis that they are not used for livestock grazing and this reduces the risk ofcompaction by grazing animals when soils are wet in Tasmania's winterand early spring.

3.8. Organic soil amendments

Organic amendments are often applied to soil in lieu of inorganicfertiliser to supply essential plant nutrients (Golabi et al., 2007) andthey contribute directly to the SOM stored in soil but their addition isdynamic rather than an inherent soil property and their effects can bepositive or negative on soil properties and plant growth. No significantresponses were found in soil physical properties or SOC after one yearfollowing application of biosolids, poppy (Papaver somniferum) mulch,and poppy seed waste, but they can be used to substitute for inorganicfertiliser in meeting plant nutrient requirements and they may be re-leasing more plant-available N than guideline assumptions.(Horticulture Innovation Australia Limited, 2016; Ives et al., 2011; Iveset al., 2015). Pyrethrum marc, a waste product of pyrethrin extraction

from dried flowers of the pyrethrum plant, can also offer benefits as asoil conditioner and as a source of nutrients for crops. Application ofpoppy waste at 200 m3 ha−1 significantly increased soil organic carbonfrom 1.24% to 1.57%, however, SOC increases resulting from lowerapplications rates were not significant and significant yield loss of up to57% of fresh market salad and lettuce occurred within 8 weeks fol-lowing waste incorporation due to a combination of increased soil pHand soil salinity (Hardie and Cotching, 2009). Compost addition wasinitially found to increase SOC and N under cropping but this changewas not maintained for a third year and there was a decrease in SOCand N under long term pasture in the first eighteen months after ap-plication of compost concomitant with an increase in pasture pro-ductivity (Ives et al., 2015). The timing application of organic amend-ments is critical to ensure that mineralisation of nitrogen from theapplied products coincides with plant nutrient requirements and thatmineralised N is not exposed to leaching loss and denitrification.

The application of biochar as a soil amendment is largely based onevidence about soil fertility and crop productivity gains made in theAmazonian Black Earth (terra preta) (Sombroek, 1966). A low-tem-perature biochar derived from acacia whole tree green waste sig-nificantly increased SOC by 23%, decreased soil bulk density and in-creased saturated hydraulic conductivity and soil water content at fieldcapacity, but had no significant effect on soil porosity or aggregatestability (Abujabhah et al., 2016a, 2016b; Hardie et al., 2014). Differ-ences were attributed to greater earthworm burrowing in the biocharamended soil. Soil chemical and physical properties were unaffected byeither biochar application at 10 Mg ha−1 or the interaction betweenbiochar and fertiliser on Red Ferrosols (Boersma et al., 2017).

High rates of biochar addition of up to 100 Mg ha−1 in a pot trialsignificantly increased TOC in three contrasting soils but no significantimpact on microbial biomass have been reported (Abujabhah et al.,2016b; Street et al., 2014). The change in TOC was associated withincreases in populations of methanotrophic and nitrifying bacteria andsignificant differences in the bacterial diversity in the Kurosol andDermosol but the Vertosol was more resilient to change (Abujabhahet al., 2017). A significant increase in SOC in the upper 0.1 m of soilresulted from the application of 20 Mg ha−1 of biochar but this wasfollowed by a downward trend over the subsequent 2 years undercropping and a positive effect on yield was also short-lived (Ives, 2013).This suggests that in a cropping regime, a once-only addition of biochardoes not provide a long term solution for maintaining SOC.

Reuse of organic materials is desirable in order to reduce wastestreams and to take advantage of the soil benefits associated with addedorganic matter and associated plant nutrients. However, there are

Fig. 6. Indicators of soil inoculum status for soil borne diseaseand/or nematode abundance in Tasmanian soils.Data source: http://soilquality.org.au

W.E. Cotching Geoderma 312 (2018) 170–182

179

difficulties associated with the physical management of materials dueto its consistency, the timing of application and the availability of nu-trients depending on product composition and consistency. A singleapplication of organic amendments may not be effective in the longterm to increase soil carbon or crop yield but applications may be re-quired at least once every two years to maintain consistent results.Quilty and Cattle (2011) concluded that organic amendments are un-likely to replace, or become more common than, inorganic inputs and itwould seem more likely that a wide range of organic products will begradually integrated into modern agriculture to help improve andsustain production systems.

4. Conclusions

Tasmanian soils store relatively large quantities of SOC due to theinherent site factors of high rainfall and cool temperatures with thegreatest stocks on Red Ferrosols under perennial pasture that are due toinherent high clay contents of iron and aluminium oxides. Tasmaniansoils store considerable SOC at depths below the current 0.3 m used incarbon accounting. Little is currently known about the dynamics of thissubsoil SOC and it warrants further investigation of how it has beeninfluenced by management and if there is potential to sequester moresubsoil SOC in Tasmania's cool wet climate. Farmers' influence on SOCis not as great as might be expected but they are still able to selectpractices that retain more SOC than others. Soils in Tasmania can be-come saturated with SOC and the greater fraction of POC measuredunder pasture may indicate that organic matter is not breaking downdue to inhibition by water logging. The nutrients in the undecomposingorganic matter are not being recycled for productive agricultural useand can lock up a considerable investment in plant available nutrients.

There are significant correlations between SOC and other physical,chemical and biological soil properties but relationships to crop yieldare weaker and harder to determine. The large store of SOM providesadvantages to productive sustainable agriculture in the form of a bufferagainst changes induced by modern agricultural practices includingtillage and compaction. SOM is dynamic and the measured and con-tinuing decrease in topsoil SOC under cropping that is associated withdegrading soil physical and chemical properties, remains an ongoingconcern for sustainable agriculture in Tasmania. The decrease of SOCunder pasture warrants further research to determine if changes inmanagement can address the decline or if factors such as climatechange are influencing these changes. It is important that monitoring ofsoil condition is continued so that trends can not only be reported onbut management actions developed and adopted.

Soil biology is controlled by both inherent and dynamic factors.Earthworm numbers are influenced by the inherent soil and site factorsof clay content and rainfall but are also dynamic due to changes in landuse and the amount of cultivation. Meso-fauna are also dynamic as theyare susceptible to the detrimental impacts of cultivation. Micro-flora areprobably the most dynamic soil biological component with consider-able variability between sites and with quick response times betweenseasons and food sources supplied by different crops. The microbialbiomass is strongly controlled by the amount of SOM present. The lackof associated soil physical and chemical data or crop yields as ex-planatory variables for changing microbial measures makes it proble-matic when advising on possible target levels for many soil microbialindicators. Research is required on how to more readily diagnose soilhealth using biological indicators. There is potential to use soil aromaas a diagnostic tool as aromatic compounds are produced by soil mi-crobes in response to environmental conditions. Soil borne diseases arealso highly dynamic, responding opportunistically to changes in the soilenvironment and potential local host plants. Farmers need to take stepsto minimise the risk of soil borne disease by growing less susceptiblecultivars and managing soil moisture to avoid either saturated or overdry soils during crop growth. They need to identify less risky paddockswith suppressive soils, i.e. those that resist diseases, in order to give

them a natural advantage for their farming business. Organic amend-ments, including biochar, provide an opportunity to reuse wastestreams in productive agriculture but multiple applications are requiredto maintain consistent increases in SOM and crop yield. They are lesseasily managed and applied than inorganic fertiliser as they are morerestricted to application when soil moisture levels are low enough toprevent soil compaction, rather than being able to be applied im-mediately before crop demand.

SOM is not simply a commodity to be traded or there to gain ben-efits in market-based instruments for carbon. This bank of SOC shouldbe viewed as a sustainability reservoir and as the potential to sequestermore soil carbon in Tasmania is small and takes decades, SOC is un-likely to provide an alternative income source to Tasmanian farmersthrough any carbon trading opportunities.

Acknowledgement

The author expresses his sincere thanks to Leigh Sparrow for re-viewing an earlier version of this manuscript.

References

Abujabhah, I.S., Bound, S.A., Doyle, R., Bowman, J.P., 2016a. Effects of biochar andcompost amendments on soil physico-chemical properties and the total communitywithin a temperate agricultural soil. Appl. Soil Ecol. 98, 243–253.

Abujabhah, I.S., Bound, S.A., Doyle, R., Bowman, J.P., 2016b. The effect of biocharloading rates on soil fertility, soil biomass, potential nitrification, and soil communitymetabolic profiles in three different soils. J. Soils Sediments 16, 2211–2222.

Abujabhah, I.S., Bound, S.A., Doyle, R., Bowman, J.P., 2017. Assessment of bacterialcommunity composition, methanotrophic and nitrogen-cycling bacteria in three soilswith different biochar application rates. J. Soils Sediments 17, 1–11. https://link.springer.com/article/10.1007/s11368-017-1733-1 (accessed 8.06.2017).

Andrews, S.S., Karlen, D.L., Cambardella, C.A., 2004. The soil management assessmentframework: a quantitative soil quality evaluation method. Soil Sci. Soc. Am. J. 68,1945–1962.

Ara, Te, 2017. Earthworms in New Zealand. In: The Encyclopedia of New Zealand, .https://teara.govt.nz/en/earthworms/page-3, Accessed date: 7 December 2017.

Baker, W.E., 1973. The role of humic acids from Tasmanian podzolic soils in mineraldegradation and metal mobilization. Geochim. Cosmochim. Acta 37, 269–281.

Baker, G.H., Thumlert, T.A., Meisel, L.S., Carter, P.J., Kilpin, G.P., 1997. Earthwormsdownunder: a survey of the earthworm fauna of urban and agricultural soils inAustralia. Soil Biol. Biochem. 29, 589–597.

Baldock, J.A., Nelson, P.N., 2000. Soil organic matter. In: Sumner, M. (Ed.), Handbook ofSoil Science. CRC Press, Boca Raton, FL, USA.

Baldock, J.A., Skjemstad, J.O., 1999. Soil organic carbon/soil organic matter. In: Peverill,K.I., Sparrow, L.A., Reuter, D.J. (Eds.), Soil Analysis: An Interpretation Manual.CSIRO, Australia, pp. 159–170.

Baldock, J.A., Sanderman, J., Macdonald, L.M., Puccini, A., Hawke, B., Szarvas, S.,McGowan, J., 2013. Quantifying the allocation of soil organic carbon to biologicallysignificant fractions. Soil Res. 51, 561–576. http://dx.doi.org/10.1071/SR12374.

Belbin, K., 2003. Soil Organic Carbon Fractions as a Measure of Land Use Impact inNorthern Tasmania. Thesis submitted in fulfilment of the requirements for degree ofBatchelor of Agricultural Science with Honours. University of Tasmania.

Blaesing, D., Rogers, G., 2016. Biofumigation. Tasmanian Farming Futures Project FactSheet. Horticulture Innovation Australia Limited, Applied Horticultural Research PtyLtd, RM Consulting Group and IPM Technologies Pty Ltd.

Blakemore, R.J., 2008. Review of Tasmanian earthworms updated from Blakemore(2000). www.annelida.net/earthworm/Tasmanian%20Earthworms/Tassie%20Earthworms.pdf, Accessed date: 7 December 2017.

Boersma, M., Wrobel-Tobiszewska, A., Murphy, L., Eyles, A., 2017. Impact of biocharapplication on the productivity of a temperate vegetable cropping system. N. Z. J.Crop. Hortic. Sci. http://dx.doi.org/10.1080/01140671.2017.1329745. (accessed 9.06.2017).

Carter, M.R., Skjemstad, J.O., MacEwan, R.J., 2002. Comparison of structural stability,carbon fractions and chemistry of krasnozem soils from adjacent forest and pastureareas in south-western Victoria. Aust. J. Soil Res. 40, 283–297.

Chan, K.Y., Roberts, W.P., Heenan, D.P., 1992. Organic carbon and associated soilproperties of a red earth after 10 years of rotation under different stubble and tillagepractices. Aust. J. Soil Res. 30, 71–83.

Chan, K.Y., Conyers, M.K., Li, G.D., Helyar, K.R., Poile, G., Oates, A., Barchia, I.M., 2011.Soil carbon dynamics under different cropping and pasture management in temperateAustralia: results of three long-term experiments. Soil Res. 49, 320–328.

Chapman, T., 2016. Investigating the Effect of Subsoil Manuring on Soil Arthropods in theNorthern Midlands of Tasmania. Thesis submitted in partial fulfilment of the re-quirements for the degree of Bachelor of Agriculture with Honours. University ofTasmania.

Chen, W., Huang, D., Liu, N., Zhang, Y., Badgery, W.B., Wang, X., Shen, Y., 2015.Improved grazing management increases soil carbon sequestration in temperatesteppe. Nat. Sci. Rep. 5, 10892. http://dx.doi.org/10.1038/srep10892 1.

W.E. Cotching Geoderma 312 (2018) 170–182

180

Close, D.C., Davidson, N.J., Watson, T., 2004. Health of remnant woodlands in fragmentsunder distinct grazing regimes. Biol. Conserv. 141, 2395–2402.

Commonwealth of Australia, 2011. Land. In: Australia State of the Environment, 110 p..https://soe.environment.gov.au/sites/g/files/net806/f/soe2011-report-land.pdf?v=1488162024, Accessed date: 15 May 2017.

Cotching, W.E., 1995. A review of the challenges for long term management of krasno-zems in Australia. Aust. J. Soil Water Conserv. 8, 18–27.

Cotching, W.E., 2009. Proof of Concept for Farm Carbon Story. (Contract Report byTasmanian Institute of Agriculture for Agricultural Resource Management and NRMNorth).

Cotching, W.E., 2010. Soil Assessment for the Waste Water Scheme of the FonterraManufacturing Site at Spreyton. Tasmanian Institute of Agricultural Research.

Cotching, W.E., 2012. Carbon stocks in Tasmanian soils. Soil Res. 50, 83–90.Cotching, W.E., Blaesing, D., 2008. Soil Microbial Indicator Tests in Northern and North

west Tasmania. Tasmanian Institute of Agricultural Research and RM ConsultingGroup.

Cotching, W.E., Kidd, D.B., 2010. Soil quality evaluation and the interaction with land useand soil order in Tasmania, Australia. Agric. Ecosyst. Environ. 137, 358–366.

Cotching, W.E., Cooper, J., Sparrow, L.A., McCorkell, B.E., Rowley, W., 2001. Effects ofagricultural management on sodosols in northern Tasmania. Aust. J. Soil Res. 39,711–735.

Cotching, W.E., Cooper, J., Sparrow, L.A., McCorkell, B.E., Rowley, W., Hawkins, K.,2002a. Effects of agricultural management on Vertosols in Tasmania. Aust. J. SoilRes. 40, 1267–1286.

Cotching, W.E., Hawkins, K., Sparrow, L.A., McCorkell, B.E., Rowley, W., 2002b. Cropyields and soil properties on eroded slopes of red Ferrosols in north-west Tasmania.Aust. J. Soil Res. 40, 625–642.

Cotching, W.E., Cooper, J., Sparrow, L.A., McCorkell, B.E., Rowley, W., 2002c. Effects ofagricultural management on Dermosols in northern Tasmania. Aust. J. Soil Res. 40,65–79.

Cotching, W.E., Cooper, J., Sparrow, L.A., McCorkell, B.E., Rowley, W., 2002d. Effects ofagricultural management on Tenosols in northern Tasmania. Aust. J. Soil Res. 40,45–63.

Cotching, W.E., Sparrow, L.A., Hawkins, K., McCorkell, B.E., Rowley, W., 2004. LinkingTasmanian potato and poppy yields to selected soil physical and chemical properties.Aust. J. Exp. Agric. 44, 1241–1249.

Cotching, W.E., Lynch, S., Kidd, D.B., 2009. Dominant soil orders in Tasmania; dis-tribution and selected properties. Aust. J. Soil Res. 47, 537–548.

Cotching, W.E., Oliver, G., Downie, M., Corkrey, R., Doyle, R.B., 2013. Land use andmanagement influences on surface soil organic carbon in Tasmania. Soil Res. 51,615–630.

Davidson, N.J., Close, D.C., Battaglia, M., Churchill, K., Ottenschlaeger, M., Watson, T.,Bruce, J., 2007. Eucalypt health and agricultural land management within bushlandremnants in the midlands of Tasmania, Australia. Biol. Conserv. 139, 439–446.

De Deyn, G.B., Raaijmakers, C.E., Zoomer, H.R., Berg, M.P., de Ruiter, P.C., Verhoef, H.A.,Bezemer, T.M., van der Putten, W.H., 2003. Soil invertebrate fauna enhances grass-land succession and diversity. Nature 422, 711–713.

Dean, C., Kirkpatrick, J.B., Friedland, A.J., 2017. Conventional intensive logging pro-motes loss of organic carbon from the mineral soil. Glob. Chang. Biol. 23, 1–11.

Don, A., Steinberg, B., Schöning, I., Pritsch, K., Joschko, M., Gleixner, G., Schulze, E.D.,2008. Organic carbon sequestration in earthworm burrows. Soil Biol. Biochem. 40,1803–1812.

Doran, J.W., Parkin, T.B., 1994. Defining and Assessing Soil Quality. In: Doran, J.W.,Coleman, D.C., Bezdicek, D.F., Stewart, B.A. (Eds.), Defining Soil Quality for aSustainable Environment. SSSA Special Publication 35. Soil Science Society ofAmerica, Madison, Wisconsin, pp. 3–21.

Doyle, R.B., 1993. Soils of the South Esk Sheet, Tasmania; Southern Half. Department ofPrimary Industry and Fisheries, Tasmania.

Doyle, R.B., 2013. Soil Organic Carbon Balances in Tasmanian Agricultural Systems.Final Research Report. Department of Fisheries, Forestry & Agriculture, Tasmania.

Eldridge, R., 2000. Land Resource Assessment Report, Lands within Burnie MunicipalArea. Department of Primary Industries, Water and Environment, Tasmania.

Ellert, B.H., Bettany, J.R., 1995. Calculation of organic matter and nutrients stored in soilsunder contrasting management regimes. Can. J. Soil Sci. 75, 529–538.

Eyles, A., Coghlan, G., Hardie, M., Hovenden, M., Bridle, K., 2015. Soil carbon seques-tration in cool temperate dryland pastures: mechanisms and management options.Soil Res. 53, 349–365.

Findlay, S., 2013. Biological cropping rotation trial. NRM North, Cuillins Pty Ltd and TasAgronomy Plus.

Finnigan, J., 2013. Green Manure and Compost Trial. Partnership Agreement: PA 206.Serve-Ag Pty Ltd and NRM North.

Friend, J.A., Richardson, A.M.M., 1986. Biology of terrestrial amphipods. Annual reviewin. Entomology 31, 25–48.

Frogbrook, Z.L., Bell, J., Bradley, R.I., Evans, C., Lark, R.M., Reynolds, B., Smith, P.,Towers, W., 2009. Quantifying terrestrial carbon stocks: examining the spatial var-iation in two upland areas in the UK and a comparison to mapped estimates of soilcarbon. Soil Use Manag. 25, 320–332.

Garnsey, R.B., 1994. Seasonal activity and aestivation of Lumbricid earthworms in themidlands of Tasmania. Aust. J. Soil Res. 32, 1355–1367.

Gentile, R.M., Perie, E., Muller, K., Deurer, M., Mason, K., van den Dijssel, C., Clothier,B.E., Holmes, A., Hardie, M., McLaren, S.J., 2016a. Quantifying the potential con-tribution of soil carbon to orchard carbon footprints. Acta Hortic. 1112, 461–466.

Gentile, R.M., Simpson, R., Mason, K., van den Dijssel, C., Clothier, B.E., Hardie, M.,Cornwall, D., 2016b. Soil carbon and nutrient services under Australian apple pro-duction systems. Acta Hortic. 1130, 33–40.

Golabi, M.H., Denney, M.J., Lyekar, C., 2007. Value of composted organic wastes as an

alternative to synthetic fertilizers for soil quality improvement and increased yield.Compost Sci.Util. 15, 267–271.

Gonzalez-Perez, J.A., Gonzalez-Vila, F.J., Almendros, G., Knicker, H., 2004. The effect offire on soil organic matter – a review. Environ. Int. 30, 855–870.

Gonzalez-Quiñones, V., Stockdale, E.A., Banning, N.C., Hoyle, F.C., Sawada, Y., Wherrett,A.D., Jones, D.L., Murphy, D.V., 2011. Soil microbial biomass—interpretation andconsideration for soil monitoring. Soil Res. 49, 287–304.

Gradwell, M.W., Arlidge, E.Z., 1971. Deterioration of soil structure in the market gardensof the Pukekohe district, New Zealand. N. Z. J. Agric. Res. 14, 288–306.

Gregorich, E.G., Carter, M.R., Angers, D.A., Monreal, C.M., Ellert, B.H., 1994. Towards aminimum data set to assess soil organic matter quality in agricultural soils. Can. J.Soil Sci. 74, 367–385.

Grose, C.J., 2015. Some insights into the health of Dermosols around Tasmania, Australia.Soil Res. 53, 710–715.

Guo, L.B., Gifford, R.M., 2002. Soil carbon stocks and land use change: a meta analysis.Glob. Chang. Biol. 8, 345–360.

Hardie, M.A., Cotching, W.E., 2009. Effects of application of poppy waste on spinachyields, soil properties, and soil carbon sequestration in southern Tasmania. Aust. J.Soil Res. 47, 478–485.

Hardie, M., Clothier, B., Bound, S., Oliver, G., Close, D., 2014. Does biochar influence soilphysical properties and soil water availability? Plant Soil 376, 347–361.

Hassink, J., 1997. The capacity of soils to preserve organic C and N by their associationwith clay and silt particles. Plant Soil 191, 77–87.

Hatley, D.L.J., Garwood, T.W.D., Johnson, P.A., 2001. The impact of changing farmingpractices on soil organic matter and soil structural stability of Fen silt soils. In: Rees,R.M., Ball, B.C., Campbell, C.D., Watson, C.A. (Eds.), Sustainable Management of SoilOrganic Matter. CABI International, Wallingford, UK, pp. 157–162.

Horticulture Innovation Australia Limited, 2016. Forthside Demonstration Site: SoilAmendments on Vegetable Crops. (Soil Wealth factsheet).

Hudson, B.D., 1994. Soil organic matter and available water capacity. J. Soil WaterConserv. 49, 189–194.

Isbell, R.F., 2002. The Australian Soil Classification, Revised Edition. Australian Soil andLand Survey Series, vol. 4 CSIRO, Melbourne.

Ives, S.W., 2013. Biological supplement trials ‘Formosa’ – Pasture & ‘Oakdene’ – Cropping.Final Report. Tasmanian Institute of Agriculture.

Ives, S.W., Cotching, W.E., Sparrow, L.A., Lisson, S., Doyle, R.B., 2011. Plant growth andsoil responses to soil applied organic materials in Tasmania, Australia. Soil Res. 49,572–581.

Ives, S.W., Sparrow, L.A., Cotching, W.E., Doyle, R.B., Lisson, S., 2015. N mineralisationfrom bioresources incubated at 12.5°C. Appl. Environ. Soil Sci. 2015, 803736.

Janzen, H.H., Campbell, C.A., Ellert, B.H., Bremer, E., 1997. Soil organic matter dynamicsand their relationship to soil quality. Dev. Soil Sci. 25, 277–291.

Jardine, P.M., Weber, N.C., McCarthy, J.F., 1989. Mechanisms of dissolved organiccarbon adsorption on soil. Soil Sci. Soc. Am. J. 53, 1378–1385.

Jenkinson, D.S., 1990. The turnover of organic carbon and nitrogen in soil. Philos. Trans.R. Soc. Lond. B 329, 361–368.

Kallenbach, C.M., Frey, S.D., Stuart Grandy, A., 2016. Direct evidence for microbial-de-rived soil organic matter formation and its ecophysiological controls. Nat. Commun.7, 13630.

Kirkby, C.A., Richardson, A.E., Wade, L.J., Passioura, J.B., Batten, G.D., Blanchard, C.,Kirkegaard, J.A., 2014. Nutrient availability limits carbon sequestration in arablesoils. Soil Biol. Biochem. 68, 402–409.

Krull, E.S., Skjemstad, J.O., Baldock, J.A., 2004. Functions of soil organic matter and theeffect on soil properties. In: GRDC Project No. CSO 00029: Residue, Soil OrganicCarbon and Crop Performance. CSIRO Land &Water, Urrbrae, South Australia.

Lal, R., 2016. Soil health and carbon management. Food Energy Secur. 5, 212–222.Lambie, S.M., 2012. Soil Carbon Loss under Pasture and Pine: Responses to Urine

Addition. Thesis, Doctor of Philosophy. University of Waikato, Hamilton, NewZealand.

Lehmann, J., Kleber, M., 2015. The contentious nature of soil organic matter. Nature 528,60–68.

Loveday, J., Farquhar, R.N., 1958. The soils and some aspects of land use in the Burnie,Table Cape, and surrounding districts, North West Tasmania. Soils and Land UseSeries No. 26 C.S.I.R.O.

Loveland, P.J., Webb, J., Bellamy, P., 2001. Critical levels of soil organic matter: theevidence for England and Wales. In: Rees, R.M., Ball, B.C., Campbell, C.D., Watson,C.A. (Eds.), Sustainable Management of Soil Organic Matter. CABI International,Wallingford, UK, pp. 23–33.

Luo, Z., Wang, E., Sun, O.J., 2010. Soil carbon change and its responses to agriculturalpractices in Australian agro-ecosystems: a review and synthesis. Geoderma 155,211–223.

Lützow, M.v, Kögel-Knabner, I., Ekschmitt, K., Matzner, E., Guggenberger, G., Marschner,B., Flessa, H., 2006. Stabilization of organic matter in temperate soils: mechanismsand their relevance under different soil conditions – a review. Eur. J. Soil Sci. 57,426–445.

Magdoff, F., 1992. Building Soils for Better Crops: Organic Matter Management.University of Nebraska Press, Lincoln.

Martens, D.A., 2000. Plant residue biochemistry regulates soil carbon cycling and carbonsequestration. Soil Biol. Biochem. 32, 361–369.

Martin, J.K., 1993. Biology of the rhizosphere. In: Soils: an Australian Viewpoint. CSIRO,Melbourne.

McDonald, D., Rodgers, D., 2010. Soils Alive! Understanding and Managing Soil Biologyon Tasmanian Farms. Department of Primary Industries, Parks, Water andEnvironment, s.

McDonald, D., Baldock, J.A., Kidd, D.B., 2009. Cradle Coast Organic Carbon MonitoringTrial. National Land and Water Resources Audit. Department of Primary Industry and

W.E. Cotching Geoderma 312 (2018) 170–182

181

Fisheries, Tasmania.McSherry, M.E., Ritchie, M.E., 2013. Effects of grazing on grassland soil carbon: a global

review. Glob. Chang. Biol. 19, 1347–1357.Mele, P.M., Carter, M.R., 1999. Species abundance of earthworms in arable and pasture

soils in south-eastern Australia. Appl. Soil Ecol. 12, 129–137.Mohamed, H.A., 2015. Arbuscular Mycorrhizal Fungi and their Influence on Growth and

Water Relations of Sweet Cherry Rootstock and Tomato Plants. Thesis submitted infulfilment of the requirements for the degree of Master of Science. University ofTasmania.

Mulvaney, R.L., Khan, S.A., Ellsworth, T.R., 2009. Synthetic nitrogen fertilizers depletesoil nitrogen: a global dilemma for sustainable cereal production. J. Environ. Qual.38, 2295–2314.

Murphy, B.W., 2015. Impact of soil organic matter on soil properties—a review withemphasis on Australian soils. Soil Res. 53, 605–663.

Osanai, Y., Flittner, A., Janes, J.K., Theobald, P., Pendall, E., Newton, P.C.D., Hovenden,M.J., 2011. Decomposition and nitrogen transformation rates in a temperate grass-land vary among co-occurring plant species. Plant Soil 350, 365–378.

Osanai, Y., Bougoure, D.S., Hayden, H.L., Hovenden, M.J., 2013. Co-occurring grassspecies differ in their associated microbial community composition in a temperatenative grassland. Plant Soil 368, 419–431.

Parry-Jones, J., 2010. The Effect of Agricultural Land Use on the Soil Carbon Fractions ofRed Ferrosols in North West Tasmania. Thesis submitted in fulfilment of the re-quirements for degree of Batchelor of Agricultural Science with Honours. Universityof Tasmania.

Paul, E.A., 2014. Soil Microbiology, Ecology and Biochemistry. Academic press.Philipps, L., 2001. The effects of all-arable organic rotations on soil organic matter levels

and the phosphorus and potassium status over the period 1987–1998. In: Rees, R.M.,Ball, B.C., Campbell, C.D., Watson, C.A. (Eds.), Sustainable Management of SoilOrganic Matter. CABI International, Wallingford, UK, pp. 294–300.

Post, W.M., Kwon, K.C., 2000. Soil carbon sequestration and land-use change: processesand potential. Glob. Chang. Biol. 6, 317–327.

Prior, L.D., Paul, K.I., Davidson, N.J., Hovenden, M.J., Nichols, S.C., Bowman, D.M.J.S.,2015. Evaluating carbon storage in restoration plantings in the Tasmanian Midlands,a highly modified agricultural landscape. The Rangel. J. 37, 477–488.

Pung, H., Olsen, J., Stirling, M., Moody, P., Pankhurst, C., Jackson, S., Hickey, M.,Cotching, W., 2003. Investigation of soil factors associated with the productivity andsustainability of vegetable production in Australia. Project No. VG99057 Report.Horticulture Australia.

Pung, H., Aird, P.L., Cross, S., 2004. The use of brassica green manure crops for soilimprovement and soil borne disease management. In: 3rd Australasian Soil-borneDiseases Symposium 8–11 February 2004, . http://www.peracto.com/publications/brassica-green-manures.pdf, Accessed date: 7 December 2017.

Quilty, J.R., Cattle, S.R., 2011. Use and understanding of organic amendments inAustralian agriculture: a review. Soil Res. 49, 1–26.

Rayment, G.E., Higginson, F.R., 1992. Australian Laboratory Handbook of Soil and WaterChemical Methods. Australian Soil and Land Survey Handbook. Inkata Press,Melbourne.

Rengasamy, P., Churchman, G.J., 1999. Cation exchange capacity, exchangeable cationsand sodicity. In: Peverrill, K.I., Sparrow, L.A., Reuter, D. (Eds.), Soil Analysis: AnInterpretation Manual. CSIRO, Australia, pp. 147–157.

Robertson, F., Crawford, D., Partington, D., Oliver, I., Rees, D., Aumann, C., Armstrong,R., Perris, R., Davey, M., Moodie, M., Baldock, J., 2016. Soil organic carbon incropping and pasture systems of Victoria, Australia. Soil Res. 54, 64–77.

Scandrett, J., Oliver, G., Doyle, R., 2010. Soil carbon depth functions under different landuses in Tasmania. In: 19th World Congress of Soil Science, Soil Solutions for aChanging World 1–6 August 2010, Brisbane, Australia, Published on DVD.

Schipper, L.A., Baisden, W.T., Parfitt, R.L., Ross, C., Claydon, J.J., Arnold, G., 2007. Largelosses of soil C and N from soil profiles under pasture in New Zealand during the past

20 years. Glob. Chang. Biol. 13, 1138–1144.Sherlock, E., 2012. Key to the Earthworms of the UK and Ireland. Field Studies Council.Sikora, L.J., Stott, D.E., 1996. Soil organic carbon and nitrogen. In: Methods for Assessing

Soil Quality. Soil Science Society of America Special Publication 49, Madison, WI53711, USA, pp. 157–167.

Skjemstad, J.O., Spouncer, L.R., Cowie, B., Swift, R.S., 2004. Calibration of theRothamsted organic carbon turnover model (RothC ver. 26.3), using measurable soilorganic carbon pools. Aust. J. Soil Res. 42, 79–88.

Soil Quality Pty Ltd, 2017. http://www.soilquality.org.au/au/tas, Accessed date: 7December 2017.

Sombroek, W.G., 1966. Amazon soils: A reconnaissance of the soils of the BrazilianAmazon region. Verslagen van Landbouwkundige Onderzoekingen. Centre forAgricultural Publications and Documentation, Wageningen, the Netherlands.

Sparrow, L.A., 2015. Six years of results from a potato rotation and green manure trial inTasmania, Australia. Acta Hortic. 1076, 29–35.

Sparrow, L.A., Wilson, C.R., 2012. Managing and Monitoring Viral and Soil-BornePathogens in Tasmanian Potato Crops. In: He, Z., Larkin, R., Honeycutt, W. (Eds.),Sustainable Potato Production: Global Case Studies. Springer, London, pp. 309–325.

Sparrow, L.A., Cotching, W.E., Cooper, J., Rowley, W., 1999. Attributes of TasmanianFerrosols under different agricultural management. Aust. J. Soil Res. 37, 603–622.

Sparrow, L.A., Belbin, K.C., Doyle, R.B., 2006. Organic carbon in coarse and fine particlesize fractions as indicators of change in Ferrosols and Sodosols under mixed farmingin Tasmania, Australia. Soil Use Manag. 22, 219–220.

Sparrow, L.A., Cotching, W.E., Parry-Jones, J., Oliver, G., White, E., Doyle, R., 2012.Changes in organic carbon and selected soil fertility parameters in agricultural soilsin Tasmania, Australia. Commun. Soil Sci. Plant Anal. 44, 166–177.

Sparrow, L.A., Rettke, M., Corkrey, S.R., 2015. Eight years of annual monitoring of DNAof soil-borne potato pathogens in farm soils in south eastern Australia. Australas.Plant Pathol. 44, 191–203.

Stevenson, G., 2011. Ruminations of a Poo-Ologist; Dung beetles in Tasmania. DunghillPress, Somerset, Tasmania.

Street, T.A., Doyle, R.B., Close, D.C., 2014. Biochar Media Addition Impacts AppleRootstock Growth and Nutrition. Hortscience 49, 1188–1193.

Syswerda, S.P., Corbin, A.T., Mokma, D.L., Kravchenko, A.N., Robertson, G.P., 2011.Agricultural management and soil carbon storage in surface vs. deep layers. Soil Sci.Soc. Am. J. 75, 92–101.

Tegg, R.S., Thangavel, T., Aminian, H., Wilson, C.R., 2012. Somaclonal selection in potatofor resistance to common scab provides concurrent resistance to powdery scab. PlantPathol. 62, 922–931.

Temple-Smith, M., Kingston, T., 1990. Role of Earthworms in Maintaining Soil Fertilityand Production of Medium-Low Rainfall Sheep Pastures. Department of PrimaryIndustry, Fisheries & Energy, Tasmania.

Temple-Smith, M.G., Kingston, T.J., Furlonge, T.L., Garnsey, R.B., 1993. The effect ofintroduction of the earthworms aporrectodea caliginosa and aporrectodea longa onpasture production in Tasmania. In: McDonald, G.K., Belotti, W.D. (Eds.),Proceedings of the 7th Australian Agronomy Conference, Adelaide, SA, Australia,September 1993. Australian Society of Agronomy Inc.. http://agronomyaustraliaproceedings.org/index.php/1993, Accessed date: 7 December2017.

Tranter, G., Minasny, B., McBratney, A.B., Murphy, B., McKenzie, N.J., Grundy, M.,Brough, D., 2007. Building and testing conceptual and empirical models for pre-dicting soil bulk density. Soil Use Manag. 23, 437–443.

Walkley, A., Black, I.A., 1934. An examination of the Degtjareff method for determiningsoil organic matter and a proposed modification of the chromic acid titration method.Soil Sci. 37, 29–38.

Wilson, B.R., Growns, I., Lemon, J., 2008. Land-use effects on soil properties on the north-western slopes of New South Wales: implications for soil condition assessment. Aust.J. Soil Res. 46, 359–367.

W.E. Cotching Geoderma 312 (2018) 170–182

182