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Effects of Land-Use Change on SoilOrganic Carbon and NitrogenZeinab Jafarian a & Ataollah Kavian aa Sari Agricultural Sciences and Natural Resources University , Sari ,IranAccepted author version posted online: 24 Oct 2012.Publishedonline: 19 Feb 2013.

To cite this article: Zeinab Jafarian & Ataollah Kavian (2013) Effects of Land-Use Change on SoilOrganic Carbon and Nitrogen, Communications in Soil Science and Plant Analysis, 44:1-4, 339-346,DOI: 10.1080/00103624.2013.741949

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Communications in Soil Science and Plant Analysis, 44:339–346, 2013Copyright © Taylor & Francis Group, LLCISSN: 0010-3624 print / 1532-2416 onlineDOI: 10.1080/00103624.2013.741949

Effects of Land-Use Change on Soil OrganicCarbon and Nitrogen

ZEINAB JAFARIAN AND ATAOLLAH KAVIAN

Sari Agricultural Sciences and Natural Resources University, Sari, Iran

Although the literature is full of references to soil degradation under forest cultivation,very little information is available on changes in soil properties following deforestationof the Hyrcanian area in northern Iran. Also, the literature provides little informationon the effects of conversion from deforested cropland to grazing, a likely direction ofland-use change in northern Iran. The objective of this study was to assess the effectof conversion of native forests into farmlands and/or grazing lands on soil proper-ties and nutrients in the Hyrcanian forest. The dominant land uses are native forest,dryland farming of barley and wheat, and grazing. Three transects were establishedon hill slopes of the study area. Transects represented three land-use changes thatoccurred from 1967 to 2004 and included mature forest (Fagus orientalis and Acervelotinom) converted to dryland farming (barley and wheat) in 1970s, dryland farm-ing converted to irrigated rice farming in mid-1980s, and dryland farming not culturedfrom 1986 to now. Average transects slope gradients were 23◦ (T1), 15◦ (T2), and 4◦(T3). Three positions (top, middle, and bottom of hill slope) were selected on eachtransect to represent each land-use type. Therefore, nine sites were selected to analyzeland-use change effects on soil properties. Twenty-m vertical transects were establishedperpendicular to main transects. At each vertical transect, three surface soil samples(0–25 cm) were collected to measure soil properties. Total nitrogen (N) was determinedby the Kjeldahl method and soil organic carbon (SOC) content was measured usingthe modified Walkley–Black wet oxidation procedure. Comparisons of mean differencesamong land uses revealed that soils under native forest contained 4.73% SOC and0.474% total N, which were significantly greater (P < 0.01) than contents under graz-ing (1.76% SOC, 0.323% total N) or dryland faming (1.37% SOC and 0.248% total N).Differences between grazing and dryland farming were not statistically significant.

Keywords Iran, land-use change, Mohammad Abad, nitrogen, organic carbon

Introduction

The pressures of human population on land resources have increased the need to appraiseland-use change effects on soil quality. One of the main factors affecting soil erosion andassociated nutrient loss is improper land use (Fu and Gulinck 1994; Islam and Weil 2000)and land-use change (Asselman, Middelkoop, and Van Dijk 2003; Glade 2003; Bakkeret al. 2005). These practices have affects both on site and off site. One of the main typesof land-use change in northern Iran is transformation of forest land to agricultural land.Evaluation of land-use changes on soil properties is of utmost importance to determine ifthere have been changes in soil quality. The effects of land-use change on soil degradationcan be assessed by comparing changes in soil organic carbon (SOC) and nutrients (Wang

Address correspondence to Ataollah Kavian, Sari Agricultural Sciences and Natural ResourcesUniversity, P. O. Box 737, Sari, Iran. E-mail: a.kavian@sanru.ac.ir

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340 Z. Jafarian and A. Kavian

and Gong 1998; Gong et al. 2006). Land-use changes, especially cultivation of deforestedland, may rapidly diminish soil quality, as ecologically sensitive components of the north-ern Hyrcanian forest ecosystem of Iran are not able to buffer the effects of agriculturalpractices.

Many studies (Reiners et al. 1994; Potter et al. 1996; Van Noordwijk et al. 1997;Hajabbasi, Jalalian, and Karimzadeh 1997; Braimoh and Vlek 2004; Breuer et al. 2006;Gong et al. 2006; Khresat, Al-Bakri, and Al-Tahhan 2008; McGrath et al. 2001; Gol 2009;Geissen et al. 2009) have shown that land-use transformation can affect soil physical andchemical properties. Often, SOC storage and soil nutrient availability are greater in forestedland than in the cropland and pastures that replace them (Lal 2002). Forest conversion tocropland can decrease SOC storage as natural vegetation is cut and decomposes, is burnt,or is replaced by crops that support lower SOC contents in the soil or aboveground plantbiomass. There is some evidence that the abandonment of agriculture and the subsequentregeneration of forest may return SOC storage to pre-agricultural amounts, although therate of recovery depends on the time frame one considers and whether the previous landuse was cropland or pasture (Post and Kwon 2000; Guo and Gifford 2002; Templer et al.2005). Soil organic matter also enhances the available water capacity. Gol (2009) reportedthat each 1% increase in organic matter adds about 1.5% to available water capacity.

The native forests in the north of Iran are undergoing a rapid conversion to agricul-tural land. Kelarestaghi and Jafarian (2011) reported forest area in parts of northern Irandecreased about 3.2% from 1967 to 2002. In this period, arable land increased by about36.9% in this region. Over a period of at least 40 years, the forests of the study areahave been transformed and deteriorated by human pressures such as deforestation andclearance for agricultural purposes, as well as harvesting for firewood and overgrazing.These rapid changes may have an impact on soil properties, which are not well under-stood. Because some properties such as SOC are important influences on soil fertility, thislack of understanding may limit proper management of soils in this region.

The objective of this study was to assess the effect of conversion of native forests intofarmlands and/or grazing lands on soil properties in the Hyrcanian forest.

Materials and Methods

Study Area Description

The study was carried out in the central parts of the Alborz Mountains, 75 km south of Saritown, Iran. The study area was located at approximately 4002080 to 4006987 meters inNorth latitude and 695634 to 704103 meters in East longitudes (UTM coordinate system,Figure 1) at an altitude of 710 to 1280 m above sea level. The region has a semi-humidclimate with a long-term mean annual rainfall of 553 mm. Minimum and maximum tem-peratures are 7.7 and 21.1 ◦C, respectively. The dominant land uses are native forest,dryland farming of barley and wheat, and grazing. The native forest is dominated by Fagusorientalis, Carpinus betulus, Quercus castanifolia, Alnus glotinisa, and Acer velotinumfspecies. The groundcover of this forest site is very rich in herbaceous plants.

Agricultural practices are mixed-farming crop cultivation and livestock rearing,mainly for subsistence. Crop production following forest clearance was started 40 to50 years ago. Pressure to find cultivatable land is enormous in the study area.

Grazing is carried out mainly on communal grazing fields and on croplands afterharvest, where dung is left in the fields to replenish soil fertility levels. Grazing fieldshave been created by transforming agricultural lands on steeper hill slopes when soil

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Effects of Land-Use Change on SOC and N 341

Figure 1. (a) Situation of Hyrcanian Forests as green parts in northern Iran. (b) Study area and threetransects. (c) Land use structure in the study area (color figure available online).

productivity decreased with intensive crop production. Plant cover of the grazing landsranges from 30% to 65% depending on the severity of grazing and soil fertility. Dominantgrass species include Chrysopogon gryllus, Festuca ovina, Bothriochloa ischaemum,Globularia trichosantha, Plantago lagopus, Lotus corniculatus, and Teucrium polium.

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342 Z. Jafarian and A. Kavian

Figure 1. (Continued)

Field Investigation and Soil Sampling

Three transects were selected on the hill slopes of the study area. These transects representtypical land-use changes that occurred in the study area from 1967 to 2002 (Kelarestaghiand Jafarian 2011) including native forest (Fagus orientalis and Acer velotinom) convertedto dryland farming (barley and wheat) in 1979 and dryland farming converted to grazingarea in 1986. These transects were located at elevations of 900 to 1165 m (T1), 850 to1150 m (T2), and 800 to 1070 m above sea level (T3) (Figure 1b). Transects lengths were1970 m (T1), 1620 m (T2), and 1810 m (T3). Three different positions from top, mid-dle, and bottom of hill slope were selected in each land-use type. Therefore, nine siteswere selected to analyze land-use change effects on soil properties in each transect. Three20-m vertical transects were established perpendicular to main transects. At each verticaltransect, three surface soil samples (0–25 cm) were collected to measure soil properties.A total of 81 soil samples were taken to measure soil physical and chemical properties inthe laboratory.

Laboratory Analysis

The soil samples were air dried and then hand sieved through a 2.0-mm mesh toremove stones, roots, and large organic particles. The particle-size distribution of the<2-mm fraction of soil was determined by the Bouyoucous hydrometer method (Geeand Bauder 1986). Total nitrogen (N) was determined by the Kjeldahl method. Theorganic carbon (OC) content was measured using the modified Walkley–Black wet oxi-dation procedure. Some important soil properties of the study area are presented inTable 1.

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Effects of Land-Use Change on SOC and N 343

Table 1Statistics for the soils properties in land uses (n = 81)

Soil properties Mean Minimum Maximum SD CV (%)

Sand (%) 21.6 3.0 51.2 6.5 30.08Silt (%) 38.7 21.0 56.0 5.9 15.22Clay (%) 39.7 23.8 53.8 5.6 14.15SOC (%) 2.58 0.314 8.029 0.639 24.77Total N (%) 0.348 0.165 0.59 0.033 9.48

Statistical Analysis

Data were analyzed using Statistical Package for the Social Science (SPSS, version 16;SPSS, Chicago, Ill.). One-way analysis of variance (ANOVA) was used to test the influenceof land-use change on soil properties and indices. The least significant difference (LSD)procedure was used to compare means of the soil properties at P ≤ 0.05. Pearson correla-tion coefficients (r) were assigned for the correlation matrix of all the variables (clay, silt,and sand contents; total N; SOC).

Results and Discussion

The coefficients of variation for soil particle content indicate that the percentage of clay hadthe least variation and greatest mean, whereas percentage of sand had the greatest variationand lowest mean. Soil organic carbon was more variable than total N (Table 1).

Comparisons of means among different land uses revealed that soils in native forestcontained more SOC and total N than those in the grazing and dryland areas (P < 0.01).No significant differences were measured between the soils in grazing and dryland areas(Table 2). The SOC and total N could be ordered as forest > grazing ≥ dry land. Theconversion of the natural forest into dry and grazing land resulted in statistically significantdecreases of SOC and total N.

These results are consistent with the findings of Khresat, Al-Bakri, and Al-Tahhan(2008), who measured a decrease in SOC when forests in northeastern Jordan were con-verted to dry farming and grazing. Soil cultivation could result in high variation in soil Ncontent (Gong et al. 2006) because of continuous cropping of the soils. When crops areharvested, the topsoil remains exposed, resulting in an increase in soil temperature andsubsequent greater rates of microbial decomposition and N transformation.

Table 2Comparisons of mean differences SOC and total N

among land uses

Land use SOC (%) Total N

Forest 4.73 (±1.66) a 0.474 (±0.061) aDry land 1.37 (±0.47) b 0.248 (±0.023) bGrazing 1.76 (±0.23) b 0.323 (±0.29) b

Values shown by different letters within the same columnsare significantly different from each other.

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Soil under forest had greater SOC than the adjacent soils’ dry land and grazing land.Relative to SOC of the forest soils, SOC contents of dryland and grazing soils decreasedby 71 and 63%, respectively. Similar to our findings, Hajabbasi, Jalalian, and Karimzadeh(1997) reported that deforestation and tillage practices resulted in a 50% decrease in soilorganic matter (SOM) For a soil depth of 0–30 cm over 20 years in the central ZagrousMountain area in Iran. Celik (2005) showed that deforestation decreased SOM by 44% and48% in soil depths of 0–10 cm and 10–20 cm, respectively, in the southern Mediterraneanhighland of Turkey. Solomon et al. (2000) also reported a 56% reduction in C and a 51%reduction in N contents during the first 3 years of cultivation of tropical woodland.

The findings indicated that soils in the native forest ecosystems have a significantlygreater organic C and total N content than those in the dry lands and grazing lands. Thismay be a result of greater organic-matter accumulation due to increased (above- and below-ground) biomass and reduced litter decomposition rates (Reicosky and Forcella 1998;Saikh, Varadachari, and Ghosh 1998).

Percentage of sand under forest was significantly greater and percentage of clay in thisland use was significantly lower than the contents under dry land and grazing, whereas nosignificant difference was observed between percentages of sand and clay under dry landand grazing (P < 0.01). Percentage of silt under dry cropping was significantly greaterthan the content under forest and grazing, whereas no significant difference was observedbetween percentage of silt under forest and grazing (Figure 2). These differences probablyreflect the fact that finer textured soils are often more productive than sandy soils and wereselectively converted to agricultural uses.

Figure 2. Comparisons of mean differences of soil particle content among land uses.

Table 3Correlation coefficients (r) of soil properties

Silt Clay SOC Total N

Sand 0.99∗∗ −0.73∗∗ 0.51∗∗ n.s.Silt n.s. −0.51∗∗ n.s.Clay −0.75∗∗ 0.38∗∗SOC 0.78∗∗Total N

∗∗Significance in level of 99%.

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Effects of Land-Use Change on SOC and N 345

Correlation coefficients in Table 3 show a strong relationship between the organic Cand total N contents (0.78). As the soil C and N cycle are tightly coupled, a change in onehas a direct influence on the other (Gol 2009). There were strong relationships betweenpercentages of sand and silt (0.99) and sand and clay (–0.73), whereas no significantrelationship was observed between percentages of silt and clay (Table 3).

Acknowledgment

We thank the research deputy of Sari Agricultural Sciences and Natural ResourcesUniversity for financial support (Project No. 04-1389-01).

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