S O I L U S E A N D M A N A G E M E N T Volume 9, Number 4, 1993 143

SCHOLEFIELD, D. & H m . , D.M. 1986. A recording penetrometer to measure the strength of soil in relation to the stresses exerted by a walking cow. Journul of Soil Science 37, 165-172.

SCHOLEFII:I.D, D., PATTO, P.M. & H.AIL, D.M. 1985. Laboratory research on the compressibility of four topsoils from grassland. Soil and Tillup Research 6, 1-16.

TABOADA, M.A. & IAVAIJO, R.S. 1988. Grazing effects on the bulk density in a Natraquoll of Argentina. j’ournul of Runge Manugrmenf 41, 502-505.

’I’ABOADA, M.A., LAVADO, R.S. & C A M I L I ~ , M.C. 1988. Cambios volumetricos en un Natracuol tipico. Ciencia del Suelo 6, 151-158.

VOMOCII., J.A. 1965. Porosity. In: Methods ./‘soil unulysis. Part 1. (ed. C.A. Black). Agronomy Society of America, Madison, Wisconsin, pp. 299-314.

response to trampling under intensive rotation grazing. Soil Science Society America j’ournul 50, 1336-1340.

WAKRLh, S.D., NF.\.II.I., M.B., BI.A(:KRUKN, W.H. & GAKZA, N.E. 1986. soil

Influence of cattle trampling on preferential flow paths in alkaline soils

M. F. Dreccer & R. S. Lavado

Abstract. Preferential flow paths (PFP) are important in water and solute movement through soils, especially in regions where vertical water movements predominate, such as the flooding Pampa (Argentina). The impact of grazing on PFP and its interactions with other properties were studied in three soils with natric horizons in the flooding Pampa using an iodide colouring technique. In the soil with a mollic horizon (Typic Natraquoll), % PFP was decreased by trampling but was later restored by shrink-swell. In the Typic Natraqualf, the most alkaline of the studied soils, % PFP was very small under both grazed and ungrazed conditions. In a coarser textured soil (Mollic Natraqualf) trampling did not affect YO PFP. The YO PFP of the Ah horizons increased with increasing organic carbon and sand contents and decreased as clay content, pH and sodium adsorption ratio (SAR) increased. The Bt horizons had small YO PFPs and were not affected by cattle trampling.

I N T R O D U C T I O N REFERENTIAL flow is important for water and solute P movement through soil. Preferential flow paths (PFP)

are regions where water fluxes are greater than elsewhere in the soil (White, 1985; Van Ommen et al., 1989). Knowledge of PFP is important in a flat area like the flooding Pampa, where water flux has a strong vertical component (Sala et ul. , 1984; Sierra & Montecinos, 1990) and salinization and alkalinization are widespread (Lavado & Taboada, 1987; 1988). PFP is often related to macroporosity (White, 1985) which is affected by soil organic matter (Hamblin & Davies, 1977; Shainberg & Letey, 1984), clay content and type (Frenkel et al., 1978), predominance of sodium in the exchange complex (Frenkel et al., 1984; Shainberg & Letey, 1984; Nielsen et al., 1986) and other factors. O n the other hand, root growth and soil fauna activity (Ehlers,. 1975; Bouma et ul., 1982) or wetting-drying cycles create macropores. Cultivation also influences macroporosity and trampling by herbivores often compacts the topsoil horizon (Mullins & Fraser, 1980; Scholefield & Hall, 1986).

P F P has been studied by different techniques. Van Ommen et al. (1988) published a simple colouring technique using the reaction of iodine with starch, which is useful for field studies. Using this technique, Van Ommen et al.

Departamento de Suelos, Facultad de Agronomia, Universidad de Buenos Aires, Avda. San Martin 4453, (1417) Buenos Aires, Argentina.

(1989) quantified the PFP in grassland and corn cropped soils. Dreccer (1990) refined this technique by taking cores and discriminating zones with different colour intensities, which were assumed to relate to the density of PFP.

I n the flooding Pampa (Argentina), cattle grazing has affected macroporosity (Taboada & Lavado, 1993) and other related physical properties of halo-hydromorphic soils, such as infiltration rate and bulk density (Taboada & Lavado, 1988; Taboada et al., 1988; Rubio & Lavado, 1990). T h e objectives of our research were (1) to measure the PFP in typical alkaline soils of the flooding pampa using the colouring technique, and (2) to study the impact of cattle trampling on P F P and other soil properties.

MATERIALS A N D M E T H O D S

Characteristics of the region T h e flooding Pampa covers 90,000 km2 of the low, flat central eastern part of Buenos Aires Province, Argentina (Fig. 1). T h e weather is temperate, subhumid in the west and humid near the Atlantic coast. There are no seasonal rainfall variations, but evapotranspiration increases in summer. T h e soils are very often saturated, waterlogged and even flooded in winter and spring, and are subjected to drought in summer (Lavado & Taboada, 1988; Sierra & Montecinos, 1990), so they undergo severe wetting-drying

144 S O I L U S E A N D M A N A G E M E N T Volume 9. Number 4. 1993

I 1

I rlrl 40° I n

I I 1 trr 5 6 O

I- \ Y

Fig 1 . 1.ocation of the flooding Pampa, and sites studied

cycles. They mainly belong to the udic or aquic regime and have natric horizons (Lavado & Taboada, 1988). The area is mainly covered by native grassland communities. Grazing histories differ across the region, as cattle and sheep ranching slowly expanded from the north at the beginning of the 17th Century to the south in the 19th Century.

Study sites Measurements were taken from June to October 1989 at three sites in the flooding Pampa (Fig. 1). One was located near Casalins village. The soil here is a Typic Natraquoll, which is the least alkaline. Treatments in this location were:

(1) a field grazed all year long, stocking rate averaging 1 .O

(2) a field ungrazed by cattle since 1976. animal unit (AU)/ha/yr,

‘The second site was near the town of Veronica; the soil is a Typic Natraqualf which is the deepest, most alkaline and clayey of the three soils studied. Treatments at this site were:

(1) a field grazed all year long, stocking rate averaging 1.1

(2) a field from which the cattle had been excluded since

(3) another field grazed throughout the year on the same

AU/ha/yr,

mid 1986.

ranch, stocking rate averaging 1.1 AU/ha/yr.

(4) a 13-year-old ungrazed enclosure.

The third site was near to Rauch city where the soil is a Mollic Natraqualf. This is the sandiest of the three and is developed over a calcrete crust. Treatmlents in this area were:

(1) a field grazed all year long, stocking rate averaging 0.8

(2) a field ungrazed since April 1987. AU/ha/yr,

All ungrazed enclosures were within grazed fields, and were 1-4 ha in area. At each site the Ah and Bt horizons were studied. The selected properties of these itwo horizons and the analytical methods used are shown in Table 1.

Determination of prejerential flow paths The PFPs were made visible using the iodide colouring technique of Van Ommen et a l . (1988, 1989). Ten 20-mm irrigations of a potassium iodide solution (7.5 g I-/]) were applied to the soil surfaces of six lm2 plots in each treatment. Previous trials indicated that, with the antecedent water content of the soil (Table I) , this rate ensures flux into deep horizons. The experiments lasted two days at Casalins and three days at Verhica and Rauch. No rain occurred during these periods and evapotranspiration was prevented with a plastic cover. One cylindrical core (6.3 cni diameter, 5 cm long) was taken with a hammer-driven core sampler from each horizon (see depth of horizons in Ta.ble 1) in the centre of each plot. Starch powder was spread over the lower face of the core and the percolating iodide was oxidized with a spray of chlorine solution. The iodide developed a blue complex with the starch thereby showing PFPs.

T o characterize PFP, maps of the six samples for each treatment and site were drawn, delineating in each of them zones lacking iodide flow from those coloured to different intensities. The differently coloured areas were discrimi- nated according to Dreccer (1990) into four categories, each having a coefficient related to its colour intensity. The coefficients were 1.00 for darkest areas with plenty of PFP; 0.50 and 0.25 represented around 50% and 25% of the most intensely coloured area; the coefficient 0.00 represented the lightest areas without PFP. PFP abundance in each core was estimated as follows:

%PFP = (0.00 x a) + (0.25 x b) + (0.50 x c) + (1.00 x d) (1)

where a, b, c and d represent the surface area occupied by each category of colour intensity, expressed as a percentage of the whole core area. Experimental data were statistically analysed by the Mann-Whitney-Wilcoxon test (Maras- cuilo & McSweeney, 1977).

RESULTS AND DISCUSSION

Figures 2-4 show PFP distributions in the Ah horizons at the three sites. The shading intensities show clear differences

S O I L U S E A N D M A N A G E M E N T Volume 9, Number 4, 1993 145

Table 1. Physical and chemical characteristics of the Ah and Bt horizons of the soils studied.

Typic Natraquoll Ah Bt

Typic Natraqualf Ah Bt

Mollic Natraqualf Ah Bt

Depth (cm) Clay (YO) (a) Silt (YO) (a) Sand (Yo) (a) Structure (b)

Ty Pe

Class Grade

Organic carbon (c) Electrical conductivity (d) PH (el Sodium adsorption ratio (f) Water content ( a )

0-11 22.9 45.8 3 1 . 3

Subangular hlocky Very fine Moderate

3.89 1.45 6.6 9.30

27.68

2 1-40 46.0 36.6 20.4

Prismatic

Medium Moderate

0.98 1.83 7.9

20.10 36.31

0-16 24.1 65.2 10.7

Massive

Medium Moderate

1.04 1.47 8.6

51.70 21.27

23-36 61.9 32.4

6.6

Columnar

Medium Moderate -

2.70 9.6

45.71 54.68

0-8 18.8 29.0 54.1

Subangular blocky Fine Weak

1.38 1.36

17.10 22.22

7.8

21-34 55.0 20.1 24.9

Prismatic

Medium Moderate -

2.80 9.0

24.30 47.55

Methods used: (a) Pipette method (Klute, 1986); (b) Soil Survey Staff (1951); (c) Walkley & Black method (Page r t al., 1982); (d) Saturation extracts (Page et al., 1982); (e) In paste (Page et al., 1982); (0 From sodium, calcium and magnesium concentrations in saturation extracts (Page et al., 1982); (g) Gravimetric method (Klute, 1986).

Ungrazed Ungrazed

.Grazed G ra ad

Fig 2. Distributions of preferential flow paths in the Ah horizon of the Typic Natraquoll at Casalins, in the ungrazed enclosure and grazed field (Black areas, PFP quantified as 1.00; narrow lined areas, PFP quantified as 0.50; wide lined areas, PFP quantified as 0.25; white areas, PFP quantified as 0.00).

between soil types and between treatments in the Typic Natraquoll (Fig. 2). Table 2 summarizes this information utilizing Equation (1).

Fig 3. Distributions of preferential flow paths in the Ah horizon of the Typic Natraqualf at Veronica, in the ungrazed enclosure and grazed field (Key as for Fig. 2).

Only in the Typic Natraquoll at Casalins (Fig. 2) were there statistically significant differences between the treatments. This soil has a mollic A horizon, which differs from the A horizons of the other two soils as it is not alkaline, has much more organic matter, and a more loamy

146 S O I L U S E A N D M A N A G E M E N T Volume 9. Number 4. 1993

Ungrazed

Grazed

Fig 4. Distributions of preferential flow paths in the Ah horizon of the Mollic Natraqualf at Kauch, in the ungrazed enclosure and grazed field ( K q as for Fig. 2).

Table 2. Preferential flow oath oercentases (% PFPs) in the Ah horizons

Ungrdzed enclosure Grazed field

Standard Standard Soil Average deviation Average deviation

Typic Natraquoll 92.6 7.9 30.8 9.4 ** Typic Natraqualf 41.5 10.3 39.0 11.3 N S Mollic Natraqualf 86.3 19.9 86.4 22.4 N S

**: significant differences between treatments (P < 0.01). NS: ditlerences between treatments not significant (P > 0.5).

texture with almost equal amounts of sand, silt and clay (Table 1). At this site the soil of the ungrazed enclosure had the largest PFP (93%) of the three sites, and exhibited the smallest coefficient of variation (7%). The latter may reflect the long period without grazing, which would have lessened the heterogeneity resulting from cattle trampling. The large difference in PFP between the grazed and ungrazed soils suggests that PFP is decreased by trampling but restored after exclusion of cattle. This recovery can be attributed to swelling and shrinking (Taboada et al., 1988). Taboada & Lavado (1993) showed that the total porosity and macroporosity ( > 30 pm) of this A horizon recovers from trampling effects in a short time.

The A horizon of the Typic Natraqualf at Veronica is structurally the most handicapped. It has the largest silt

Unqrazed

Grazed

Fig 5. Distributions of preferential flow paths in the Ut horizon of the Typic Natraquoll at Casalins, in the ungrazed enclosure and grazed field (Key as for Fig. 2).

content and greatest alkalinity, and also the least organic matter (Table 1); it has massive structure, is very dispersable and its structural stability is poor in both ungrazed and grazed areas (Alconada, 1991). The YO PFP was the least of the three sites and showed no significant difference between ungrazed and grazed areas (Fig. 3, Table 2). The mean coefficient of variation of PFP was 25% for both treatments. The YO PFP of the thirteen year old ungrazed enclosure did not differ significantly from that of the surrounding grazed soil (the PFP of both treatments averaged SO%), although at this enclosure the coefficient of variation (1 %) was much less than that of the grazed area (coefficient of variation 30%). The large amount of exchangeable sodium (high SAR) and small organic matter content (Table 1) are probably the main causes of both the pore collapse and the lack of the PFP regeneration where the soil is ungrazed.

In the Mollic Natraqualf of Rauch, unlike the Typic Natraqualf of Veronica, % PFP was large in both grazed and ungrazed areas (Fig. 4, Table 2). The '/o PFP of the soil of the grazed area was the largest of the three studied sites. The coefficient of variation averaged 22% in both treatments. The alkalinity of this soil is much less and the organic matter content greater than that of Veronica (Table 1). The coarser texture (54% sand compared with only 11%

S O I L USE AND MANAGEMENT Volume 9, Number 4, 1993 147

Ungrazed Ungrazed

Grazed Grazed

Fig 6. Distributions of preferential flow paths in the Bt horizon of the Typic Natraqualf at Veronica, in the ungrazed enclosure and grazed field (Key as for Fig. 2).

at Veronica) helps the soil resist compaction by trampling (Van Haveren, 1983). This result agrees with the report of Rubio & Lavado (1990), who found little variation in total porosity in this Mollic Natraqualf.

Figures 5-7 show the PFP distributions in the Bt horizon at each site. The % PFPs of the three Bt horizons were less than those of their respective Ah horizons, and the coefficients of variation were greater. Bt horizons are too deep to suffer from hoof impact and consequently showed no differences in YO PFP between grazed and ungrazed treatments at each location. However, there are large differences in % PFP between sites (Table 3), which can be related to soil characteristics (Table 1). In the Typic Natraqualf of Veronica, which has the largest clay content,

Table 3. Preferential flow path percentages (Yo PFPs) in the Bt horizons

Ungrazed enclosure Grazed field

Standard Standard Soil Average deviation Average deviation

Typic Natraquoll 27.8 11.2 19.9 9.3 NS Typic Natraqualf 12.6 16.0 4.6 8.6 NS Mollic Natraqualf 32.8 12.2 32.5 19.8 NS

NS: differences between treatments not significant ( P > 0.05).

Fig 7. Distributions of preferential flow paths in the Bt horizon of the Mollic Natraqualf at Rauch, in the ungrazed enclosure and grazed field (Key as for Fig. 2).

greatest alkalinity and greatest SAR values of the three (Table I), the Bt horizon had the smallest YO PFP. The natric horizons of the other two soils have similar SAR values, but the Mollic Natraqualf at Rauch, with a large sand content, has the largest '/O PFP.

C O N C L U S I O N S

This simple and non expensive technique was useful for comparing the impact of grazing on YO PFP of different soils. The soils with greater organic carbon or sand contents had larger YO PFPs, and the greater the alkalinity (pH, SAR value) or clay content the smaller the YO PFP observed.

R E F E R E N C E S

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BOUMA. J., BELMANS, C.F.M. & DEKKER. L.W. 1982. Water infiltration and redistribution in a silt loam subsoil with vertical worm channels. Soil Science Society of America Journal 46, 97 1-921.

DRECCKR, M.F. 1990. Esiudio de Jujos prefirenczales de uguu rn suelos

148 S O I L U S E A N D M A N A G E M E N T Volume 9, Number 4, 1993

hulomdrfirus. Undergraduate thesis, Facultad de Agronomia, Universidad de Buenos Aires.

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FRI.NKCI., H., GOER.IYF,N. J.O. & RI-IOAIXS, J.D. 1978. Effects of clay type and content, exchangeable sodium percentage and electrolyte concentra- tion on clay dispersion and hydraulic conductivity. Soil Science Society Amerrcun Juurnal42, 32-39.

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Kutiro, G. & LAVKX), R.S. 1990. Effectos de alternativas de manejo pasturil sobre la densidad aparente de un suelo con horizonte natrico. Ciencia del Suelu 8, 79-82.

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la prov. de Buenos Aires, Argentina. Hydrology on large llarlanda. Proceedings o f t h e Olauarrlh Symposium Vol. 11, 973-1009.

SC.HOL.EFIELD. D. & HAIL. D.M. 1986. A recording penetrometer to measurc the strength of soil in relation to the stresses exerted by a walking cow. Journal of Soil Science 37, 165-172.

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TAIIOALIA. M.A. & LAVADO, R.S. 1993. Influence of cattlc trampling on soil porosity under alternate dry and ponded conditions. Soil L!w und Managemrnr 9, 139-143.

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VAN OMMEN, H., DIKSMA, R., HENI)RICKN, J.M.H., 1)lKhl.K, L.W.,

The use of soil in colliery spoil reclamation

A. Gildon''2 & D. L. Rimmer'

Abstract. Field trials measured the benefits of using soil in the reclamation of colliery spoil. Increasing the thickness of the soil cover increased grass yield, particularly on a site with potentially acidic spoil materials. Mixing soil with the underlying spoil increased yield slightly compared to using the same amount of soil as a cover. From these and earlier results, we conclude that: the use of soil as a cover is essential on sites with acidic, or potentially acidic, spoil; to be effective in the short-term, the thickness of soil can be as little as 15 cm; the use of soil on sites with non-acidic spoil is beneficial in terms of physical conditions, such as improved water-holding capacity and better root penetration; the benefits of incorporating the soil on such sites are probably insufficient 1'0

justify the additional effort involved.

INTRODUCTION

N EARLIER field trial (Rimmer & Gildon, 1986) showed A beneficial effects, in terms of herbage yield and soil conditions, from the addition of soil in the reclamation of

'Department of Agricultural & Environmental Science, T h e University, Newcastle upon Tyne NEI 7RU, UK 'Present address: Zeneca Pharmaceuticals, Alderley Park, Macclesfield, Cheshire SKI0 4TG, UK

colliery spoil, the coarse rock waste derived from underground coal mining. The improved soi I conditions included chemical, physical and biological properties. In a follow-up study, soil-covered reclamation sites wcrc surveyed to assess the biological activity in the soil cover (Gildon & Rimmer, 1993). This showed that, on sites with acidic spoil, increasing thickness of soil cover resulted in a more favourable surface pH and hence increased biological activity.