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Published online 6 May 2005
Published in Soil Sci Soc Am J 69:893-901 (2005)
DOI: 10.2136/sssaj2004.0280
© 2005 Soil Science Society of America
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Soil & Water Management & Conservation

Influence of Grass and Agroforestry Buffer Strips on Soil Hydraulic Properties for an Albaqualf

Tshepiso Seobia, S. H. Andersonb,*, R. P. Udawattac and C. J. Gantzerb

a North West Provincial Dep. of Agriculture, Soil Science Section, Private Bag X804, Botha Street, Potchefstroom, South Africa 2520
b Dep. of Soil, Environmental and Atmospheric Sciences, 302 Anheuser-Busch Natural Resources Building, Univ. of Missouri, Columbia, MO 65211
c Center for Agroforestry, 203 Anheuser-Busch Natural Resources Building, Univ. of Missouri, Columbia, MO 65211

* Corresponding author (AndersonS{at}missouri.edu)


   ABSTRACT
TOP
 NOTES
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Agroforestry production systems have been introduced in temperate regions to improve water quality and diversify farm income. Agroforestry and grass–legume buffer effects on soil hydraulic properties for a Putnam soil (fine, smectitic, mesic Vertic Albaqualf) were evaluated in a corn (Zea mays L.)–soybean [Glycine max (L.) Merr.] watershed in northeastern Missouri. The no-till management watershed was established in 1991 with agroforestry buffers implemented in 1997. Agroforestry buffers, 4.5 m wide and 36.5 m apart, consist of redtop (Agrostis gigantea Roth), brome (Bromus spp.), and birdsfoot trefoil (Lotus corniculatus L.) with pin oak (Quercus palustris Muenchh.), swamp white oak (Q. bicolor Willd.), and bur oak (Q. macrocarpa Michx.) trees. Soil cores (7.6 cm in diam. by 7.6 cm long) were collected from the treatments from four 10-cm depth increments to determine saturated hydraulic conductivity (Ksat), soil water retention, pore-size distributions, and bulk density. Bulk density was 2.3% lower (P < 0.05) within the grass and agroforestry buffers compared with the row crop areas. Total porosity and coarse mesoporosity (60- to 1000-µm diam.) were 3 and 33% higher (P < 0.05), respectively, for the grass and agroforestry buffer treatments than the row crop treatment. The Ksat was three and 14 times higher (P < 0.05) in the grass and agroforestry buffer treatments compared with the row crop treatment. Results show that the grass and agroforestry buffer treatments increased potential water storage by 0.90 cm and 1.1 cm per 30-cm depth compared with the row crop treatment. Although the claypan horizon will dominate the surface hydrology, buffers may provide some benefit by reducing runoff from row crop management.

Abbreviations: Ksat, saturated hydraulic conductivity • pHw, water pH


   INTRODUCTION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
EXCESSIVE SURFACE WATER RUNOFF is a principal cause of erosion and nonpoint-source pollution. Land with steep slopes under row crop management has been managed with terraces and surface water drainage systems to protect soil from erosion (Schwab et al., 1993). However, construction of terraces and drains is expensive and only economical for higher-value crops (Countryman and Murrow, 2000).

Contour strip cropping has been identified as a cropping system that reduces runoff velocity and soil loss (Martin et al., 1976; Schwab et al., 1993). Strip cropping uses strips of row crops having a wide row spacing alternating with crops having a narrow row spacing. This system is more effective if tillage and planting are performed along the contour. Schwab et al. (1993) estimated soil loss with the universal soil loss equation to be as low as 5.1 Mg ha–1 yr–1 for strip cropping, which was comparable with soil loss with terraces. Grass buffer strips reduce runoff and increase infiltration upslope from the strips; Schmitt et al. (1999) observed that doubling the width of a 7.5-m-wide grass strip doubled water infiltration into the soil. A multispecies riparian buffer increased the infiltration rate five times compared with cultivated and grazed fields (Bharati et al., 2002). The infiltration rates for components of the riparian buffer were as follows: silver maple (Acer saccharum Marsh.) > smooth brome (Bromus inermis Leyss), timothy (Phleum pretense L.), and Kentucky bluegrass (Poa pratensis L.) grass filter > switchgrass (Panicum virgatum L.). They showed that planting buffers can improve infiltration within 8 to 10 yr. Other studies also have demonstrated that perennial vegetation can increase infiltration (Broersma et al., 1995; Wood, 1977).

Recently, a study was conducted to evaluate the effects of grass and agroforestry contour buffer strips on runoff, sediment, and nutrient losses on a claypan soil (Udawatta et al., 2002). They found that these buffers reduced surface water runoff, sediment, total P, and total N losses 2 yr after grass and tree establishment compared with a control watershed. The grass and agroforestry strips reduced runoff, total P and total N, although the agroforestry buffer strips failed to significantly reduce sedimentation. Grass and agroforestry strips reduced water runoff by about 9%.

Soil properties are very important in selecting soil conservation systems. Soil type and texture greatly influence soil water movement and storage (Klute and Dirksen, 1986). Claypan soils have a shallow topsoil layer, usually a silt loam texture, with sufficient water transmission pores. However, this surface horizon is underlain by a high clay content subsoil horizon (Blanco-Canqui et al., 2002; Crockroft and Olsson, 1997; Motavalli et al., 2003; Wang et al., 2003) which inhibits downward water movement and enhances surface water, nutrient (Blevins et al., 1996; Kelly and Pomes, 1998), and herbicide (Blanchard and Donald, 1997) runoff. Blanco-Canqui et al. (2002) studied Ksat throughout the profile of a claypan soil. They found Ksat to be very low (0.002 mm h–1) within the claypan subsoil horizons relative to surface horizons (70 mm h–1) for these soils, which increases runoff and subsequent soil loss.

Little is known comparing the impacts of grass and agroforestry buffer strip practices on hydraulic properties for claypan soils. The purpose of this study was to evaluate the effects of grass and agroforestry buffers on soil hydraulic properties for a claypan soil at a watershed study site in northeastern Missouri (Udawatta et al., 2002). The objective of the study was to measure and compare soil water retention, pore-size distributions, bulk density, and Ksat for grass buffer, agroforestry buffer, and row crop treatments.


   MATERIALS AND METHODS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Experimental Site
The experimental watershed used for this study is located at the Greenley Memorial Research Center near Novelty, MO (Fig. 1). The study site was located in a north-facing watershed that was demarcated in early 1991. The watershed was under a corn–soybean rotation, with no-till land preparation and contour planting (Udawatta et al., 2002). The average soybean and corn yields from 1992 through 2000 were 2.755 Mg ha–1 (1.680–3.699 Mg ha–1) and 8.500 Mg ha–1 (5.017–10.660 Mg ha–1), respectively; yield data were not available for 1991. Runoff water quality is being monitored to determine nutrient, herbicide, and sediment losses from the watershed.



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  		Fig. 1. Topographic map of study site with 0.5-m elevation interval contour lines (thin black lines), agroforestry buffer strips (wide gray lines), and sampling region (superimposed box). A grass waterway is located at the outflow end of the watershed (wider gray line; modified from Udawatta et al., 2002). The inset map shows location of watershed in Missouri.

 
The 4.44 ha agroforestry watershed consists of 4.5-m-wide buffer strips at 36.5 m apart (22.8 m at lower slope positions) (Fig. 1). The agroforestry buffer strips are composed of grasses, legumes, and trees which were established in 1997. The grass–legume combination planted throughout the buffer strips included redtop, brome grass (Bromus spp.), and birdsfoot trefoil. Pin oak, swamp white oak, and bur oak trees were planted in the center of the buffer strips at 3-m spacing. Trees were planted in a 75-cm-deep hole created by a 45-cm-diam. auger. The holes were back filled with loosened soil corresponding to appropriate horizons to establish a suitable planting location.

The treatments for this study included the row crop area and two locations within the contour buffer. The two treatments within the contour buffer are referred to as the grass buffer treatment, which was in the grass–legume areas 150 cm distant from trees, and the agroforestry buffer treatment, which was 20 cm distant from a pin oak tree trunk in undisturbed soil (diameters of tree trunks were about 6 cm).

The soils in the agroforestry watershed were mapped as Putnam silt loam and Kilwinning silt loam (fine, smectitic, mesic Vertic Epiaqaulf). The soils have a drainage restrictive B horizon (claypan) at variable depths between 4 and 37 cm (Udawatta et al., 2002). Restrictive claypans produce surface runoff during high rainfall periods in combination with periods of lower evapotranspiration during the winter, spring, and early summer. The experimental site for this study was conducted only on the Putnam silt loam.

Soil samples from six profiles from the watershed were analyzed by horizon in 2000. Clay content, silt content, cation exchange capacity, organic C, and water pH (pHw) data for the upper soil horizons of the agroforestry watershed are presented in Table 1. In the study area, the claypan on the average occurred at about the 38 cm depth.


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  		Table 1. Soil physical and chemical properties by horizon for the Putnam silt loam in the agroforestry watershed (5000 m2 area, 1 to 2% slope).

 
Sampling Procedures
Undisturbed soil cores, 7.6 cm in diam. and 7.6 cm in length, were taken to determine soil water retention, bulk density, and Ksat. The cores were taken on 19 June 2003 from the watershed for the agroforestry buffer, grass buffer, and row crop treatments (Fig. 1).

Soils from the second and the third contour buffer strips counting from the southern edge of the watershed were sampled for the agroforestry and grass buffer treatments. For the agroforestry buffer treatment, soils were sampled 20 cm from six pin oak trees (three trees each from the second and third buffers). For the grass buffer treatment, samples were taken midway between two trees (1.5 m from trees). Six replicate locations were chosen with three in the second buffer and three in the third buffer. For the row crop treatment, three samples were taken midway between the second and third buffers (18 m from buffers) with three additional samples taken midway between the third and fourth buffers. Cores were taken from four depths: 0 to 10, 10 to 20, 20 to 30, and 30 to 40 cm. Each core was trimmed, sealed in a plastic bag, transported to the laboratory, and stored at 4°C before measurements were conducted.

Laboratory Analyses
Cores were removed from cold storage, covered with cheese-cloth at the bottom, and then saturated in tubs with water before Ksat and water retention were measured. The electrical conductivity of the water was 0.68 dS m–1 and the sodium absorption ratio was 2.34. A syringe was used to apply bentonite slurry, mixed at an 8:1 ratio of bentonite to water, to seal the samples along the core walls and plug visible macropores on the core surface. The purpose of sealing was to remove boundary flow along the core edge and to evaluate the effects of treatments on the soil matrix excluding macropores since these disappear with depth (Blanco-Canqui et al., 2002). The constant head method was used for Ksat determination, while the falling head method was used on some samples with very low Ksat values (Klute and Dirksen, 1986).

Soil cores were resaturated for water retention measurements. Water retention was measured in funnels with ceramic plates at –0.4, –1.0, –2.5, –5.0, –10, and –20 kPa soil water pressures (Klute, 1986). Soil cores were air dried at 35°C to a constant weight. A subsample was oven-dried to determine water content that was used in determining soil bulk density. Bulk density was calculated using the air-dried core mass, the water content from the oven-dried subsample, and the core volume. Air-dried cores were sliced into cross-sections for further measurement at the –33 kPa soil water pressure (Klute, 1986). The –33-kPa pressure retention was measured using soil aggregates in pressure chambers.

The capillary rise equation was used to estimate effective pore sizes from water retention measurements (Ghildyal and Tripathi, 1987). Pore sizes were divided into four classes: macropores (>1000-µm effective diam.), coarse mesopores (60- to 1000-µm effective diam.), fine mesopores (10- to 60-µm effective diam.), and micropores (<10 µm effective diam.; Anderson et al., 1990). The saturated core water content at 0 kPa soil water pressure was used to determine total porosity.

Statistical Analysis
Homogeneity of variance tests were conducted to check for variability within treatments for each soil hydraulic property measured due to the systematic arrangement of treatments. Analysis of variance was further conducted with SAS using the GLM procedure when variances within treatments were homogeneous (SAS Institute, 1999). Data for all properties had homogeneous variances. Contrasts between treatments were also determined; these were divided into row crop vs. others and grass buffer vs. agroforestry buffer. Least significant differences (Duncan's LSD) were calculated to find significant differences between treatments at each soil depth. An estimate for the LSD between treatments at the same depth or different depths was obtained using the Mixed procedure in SAS. The Ksat data were found to be log-normally distributed and were log-transformed for statistical analyses. Statistical differences were declared significant at the {alpha} = 0.05 level.


   RESULTS AND DISCUSSION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSIONS
 REFERENCES
 
Soil Water Retention
Soil water retention as a function of soil water pressure was different among treatments for the 0.0-kPa pressure (Table 2). The row crop vs. others contrast was different at both 0.0 and –0.4 kPa, while the grass buffer vs. agroforestry buffer contrast was not different for any soil water pressure. The water contents at 0.0 and –0.4 kPa were higher (3%) for the two buffer treatments compared with the row crop treatment. Scott and Wood (1989) found that 12 to 30 years of tillage of a Crowley silt loam (Albaqualf) lowered water retention at –10 kPa soil water pressure when compared with a virgin prairie and 1 yr of tillage. Messing et al. (1997) found no differences in soil water retention between grass pasture and trees for a high clay content soil, while soil under tree management had higher soil water retention than soil under pasture for sandy-textured soils. These findings support our observations in the current study.


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  		Table 2. Average soil water content as a function of soil water pressure (0.0 to –33 kPa) for the row crop, grass buffer, and agroforestry buffer treatments and soil depths, and the ANOVA.

 
There were differences in soil water retention due to soil depth for all measured soil water pressures (Table 2). Generally, soil water content for a selected pressure was higher in the 0- to 10-cm depth compared with the 10- to 20-cm depth for soil water pressures > –20 kPa. Differences in total soil porosity (higher porosity in the surface depth compared with the second depth, Table 3) were a possible reason for this result. There was an increase in water content from the second through the fourth soil depth for all soil water pressures. This was probably because of the increase in clay content through these subsoil horizons (Table 1). There were interactions between treatment and soil depth for soil water pressures > –5.0 kPa, while there were no interactions at lower soil water pressures. These interactions were due to the lower soil water contents at shallow depths for the row crop treatment but higher water contents at deeper depths for this treatment compared with the buffer treatments. This was because of more erosion for the row crop treatment and a subsequent shallower depth to a higher increase in clay content for this treatment.


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  		Table 3. Total pores, macropores, coarse mesopores, fine mesopores, and micropores for the row crop, grass buffer and agroforestry buffer treatments and soil depths, and the ANOVA.

 
Differences among treatments for specific soil depths are shown in Fig. 2. For the first soil depth, higher soil water content was present for the two buffer treatments compared with the row crop treatment for the 0.0- and –0.4-kPa pressures (Fig. 2A). Water content for the grass buffer treatment was higher compared with the row crop treatment for the –1.0-kPa pressure at this depth (Fig. 2A). These results were possibly due to more root development in the buffer treatments with subsequent higher porosity compared with the row crop treatment. Water content at the 0-kPa pressure was higher for the agroforestry buffer treatment compared with the row crop treatment in the 0- to 30-cm depth (Fig. 2A–C). The row crop treatment had higher water content from –1.0 to –20 kPa compared with the buffer treatments at the fourth depth (Fig. 2D). This was probably because of more soil erosion in the row crop treatment and a subsequently shallower depth to the claypan horizon, which resulted in higher soil water contents at these pressures.



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  		Fig. 2. Soil water retention curves for row crop (RC), grass buffer (GB), and agroforestry buffer (Ag) treatments at depths of (A) 0 to 10 cm, (B) 10 to 20 cm, (C) 20 to 30 cm, and (D) 30 to 40 cm. Bars indicate LSD (0.05) values and are presented at pressures when significant differences occurred among treatments.

 
Pore-Size Distributions
Buffer treatments and soil depth had effects on total porosity and coarse mesoporosity (Table 3). Soil depth also had an effect on fine mesoporosity and microporosity. The row crop vs. others contrast indicated that the buffer treatments had more total porosity and coarse mesoporosity compared with the row crop treatment. Coarse mesoporosity was also greater in the agroforestry treatment compared with the grass buffer treatment. More root development under the buffer treatments and their subsequent effect on pore volume probably caused this increase.

In Iowa, five times greater infiltration was found in soils under multispecies riparian buffers compared with a crop site; this increase was attributed to a larger number of macropores (Bharati et al., 2002). Root decay and soil fauna activity were responsible for the development of more macropores under silver maple. Gray (1973) observed three to six times greater infiltration under forest cover compared with row crop management, and he attributed these differences to increased porosity. Results obtained from the current study are similar to previous studies in terms of greater increases in porosity for buffer treatments; however, significant increases in macroporosity were not found probably due to variability among replicates. No differences among treatments were found for macroporosity, fine mesoporosity, and microporosity.

Soil depth had an effect on all pore-size classes except for macropores (Table 3). Porosity decreased from the surface depth to the second depth for all pore-size classes except for microporosity. This was because of an 11% increase in bulk density from the first to the second depths (Table 4). There was an increase in porosity with depth from the third to the fourth depths for all size classes except for macroporosity and coarse mesoporosity. Microporosity increased as a function of depth probably due to increasing clay content with depth for this soil (Table 1). There was an interaction between treatment and depth only for total porosity. This interaction was due to the lower porosity at shallow depths for the row crop treatment but higher porosity at deeper depths for this treatment compared with the buffer treatments.


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  		Table 4. Geometric means of saturated hydraulic conductivity (Ksat) and arithmetic means of bulk density for the row crop, grass buffer, and agroforestry buffer treatments and soil depths, and the ANOVA.

 
Porosity values for the buffer treatment and soil depth combinations are presented in Table 3. Total porosity was different among treatments for all four depths. Total porosity for the two buffer treatments was 9% higher than porosity in the row crop treatment for the first depth. Total porosity in the agroforestry buffer treatment was also found to be greater compared with the row crop treatment for the first three soil depths; however, porosity in the row crop treatment was higher than the grass buffer treatment for the fourth soil depth. Differences among treatments for coarse mesoporosity also existed (Table 3, Fig. 3B). Coarse mesoporosity was greater in the buffer treatments compared with the row crop treatment for the first soil depth. The agroforestry buffer treatment had greater coarse mesoporosity compared with the row crop treatment for all soil depths. No differences existed among treatments for macroporosity, fine mesoporosity, and microporosity for all four depths (Table 3; Fig. 3A, 3C, 3D). Carter et al. (1994) observed lower fine mesopores and micropores (≤50-µm diam.) on one orchard grass (Dactylis glomerata L.) cultivar compared with two tall fescue (Festuca arundinacea) cultivars in Charlottetown fine sandy loam. In the study by Obi (1999), 5-yr-old grass treatments increased macroporosity (≥50-µm diam.) by 21.1%, while this treatment decreased microporosity by 13.6%, compared with a bare soil treatment with a Paleustult soil. These results are different than our findings since we were unable to find increases in macroporosity for the buffer treatments.



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  		Fig. 3. Porosity values for selected pore-size classes for row crop (RC), grass buffer (GB), and agroforestry buffer (Ag) treatments as influenced by soil depth. Pore-size classes include (A) macropores (>1000-µm diam.), (B) coarse mesopores (60- to 1000-µm diam.), (C) fine mesopores (10- to 60-µm diam.), and (D) micropores (<10-µm diam.). Bars indicate LSD (0.05) values and are presented for pore-size classes with significant differences among treatments.

 
Messing et al. (1997) examined macroporosity for two high-clay-content soils and three high-sand-content soils under 30-yr-old trees and a grass pasture site. They found no increase in macroporosity for the high clay soils under trees as compared with grass pasture. This result supports observations in our study. They did find increases in macroporosity under forest management for the three sandy-textured soils. Cadisch et al. (2004), Dierolf et al. (1997), and van Noordwijk et al. (1991) indicated that trees are often found to increase macroporosity, an affect which also influences nutrient mobility under agroforestry management systems. In contrast to our results, studying 10-yr-old grass hedges, Rachman et al. (2004) concluded that warm-season grasses increased macroporosity compared with row crop areas in the top 20 cm of a deep loess soil (Typic Hapludoll). Trees may have an effect on porosity at deeper soil depths compared with grasses due to their root distribution patterns. Studying root distributions of oaks in Missouri, Udawatta and Henderson (2003) found approximately 22% of the roots in the 50- to 150-cm depth within a 150-cm profile. In contrast, grass roots have shallower depth distribution patterns.

Bulk Density
Differences in bulk density occurred among treatments and soil depths. Interactions between treatments and soil depth also occurred (Table 4). Bulk density was lower for the buffer treatments compared with the row crop treatment. Bulk density increased in the second and third depths relative to the first depth. The lowest bulk density was found in the fourth depth as expected probably due to higher concentrations of smectitic clays and their associated swelling.

Bulk density was lower for the buffer treatments compared with the row crop treatment for the first depth (Fig. 4A, Table 4). For the second depth, bulk density was higher for the grass buffer and row crop treatments compared with the agroforestry treatment. There were no differences among treatments for the lower two soil depths.



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  		Fig. 4. (A) Bulk density and (B) saturated hydraulic conductivity (Ksat) for row crop (RC), grass buffer (GB), and agroforestry buffer (Ag) treatments as influenced by soil depth. (A) The bar indicates the LSD (0.05) value for bulk density, and (B) the LDS (0.05) value for Ksat is listed on the graph due to the log scale.

 
Messing et al. (1997) found smaller bulk density values under trees compared with grass pasture; but this was only within the top 15 cm across high and low clay content soils. This agrees with our results where only the top 20 cm had lower bulk density values due to the agroforestry treatment.

Literature supports the fact that mature trees reduce soil bulk density at lower soil depths than found in the study. A 3- to 9-yr-old eucalyptus tree (Eucalyptus tereticornis Sm.) plantation reduced bulk density in the soil layers between 0 and 150 cm for an Aquatic Petrocalcic Natrustalf (Mishra et al., 2003) when compared with a barren control treatment. Soil bulk density was lowered by the N-fixing, deep rooting, and heavy litter tree species when compared with a pasture treatment for a Typic Tropohumults soil (Fisher, 1995). Five-year-old grass and legume treatments had lower bulk density (1.40 g cm–3) compared with a bare soil treatment (1.52 g cm–3; Obi, 1999). Since trees in the current study are young (6 yr old), the effects on deeper soil horizons have not yet been expressed. It is anticipated that, as trees mature and their roots occupy more soil volume, greater changes in porosity will occur both in shallow and deeper soil horizons.

Saturated Hydraulic Conductivity
There were differences in Ksat among treatments, soil depths, and treatment x depth interactions. The Ksat was higher for the agroforestry and grass buffer treatments compared with the row crop treatment (Table 4). The Ksat for the agroforestry treatment was three times higher compared with the grass buffer treatment, and 14 times higher compared with the row crop treatment. The Ksat decreased from the first depth to the second due to an increase in bulk density (Table 4). The lowest values were measured in the fourth depth because of the higher concentration of smectitic clay in this horizon.

The Ksat was higher for the agroforestry buffer treatment compared with the grass buffer and row crop treatments for all depths except the second depth, where it was only higher than the grass buffer treatment (Table 4, Fig. 4B). The large difference in Ksat for the fourth depth among treatments is probably due to the differences in soil erosion for the row crop area and subsequent sampling within the claypan horizon for this treatment for the 30- to 40-cm depth. The Ksat for the grass buffer treatment was not different from the row crop treatment for all depths. Obi (1999) measured nearly six times greater Ksat for a 5-yr-old grass compared with bare soil (316.7 vs. 54.1 mm h–1). Results from this study show similar increases in measured Ksat.


   CONCLUSIONS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
REFERENCES
 
This study was conducted to test the hypothesis that agroforestry and grass buffer strips improve soil hydraulic properties compared with a row crop treatment. Soil water retention, pore-size distribution, bulk density, and Ksat were compared for the three treatments at four soil depths.

The row crop treatment had lower water content than the two buffer treatments at 0 and –0.4 kPa soil water pressure. These differences were attributed to the enhanced porosity created by the buffer treatments. The agroforestry buffer (0.53, 0.096 m3 m–3) and the grass buffer (0.52, 0.085 m3 m–3) treatments had greater total porosity and coarse mesoporosity (pores 60–1000 µm in diam.) than the row crop treatment (0.51, 0.068 m3 m–3). For bulk density, buffer treatments had a lower value (1.30 g cm–3, both buffer treatments averaged across depths) compared with the row crop treatment (1.33 g cm–3). Differences in bulk density among treatments existed for the first two sampling depths, but not the lower two depths. The Ksat values for the agroforestry buffer treatment were higher than those of the other two treatments for the first, third, and fourth sampling depths.

Total porosity data from this study show that grass buffer and agroforestry buffers after six years can store more water (0.9 and 1.1 cm, respectively) in the upper 30 cm of soil compared with the row crop treatment. While these values are not large, they do indicate the advantage of these plants in a buffer system. In terms of runoff reduction, the main advantage of these buffers probably occurs due to increased transpirational water use by the buffer plants especially during fallow periods (data not included).

From these results, it is apparent that the agroforestry and grass buffer treatments do influence some soil hydraulic properties in claypan soils. It is possible that water may infiltrate the agroforestry buffer treatment better compared with the row crop treatment. If this occurs, lower runoff and less sediment, nutrient, and herbicide losses will occur in watersheds managed with this buffer treatment.


   ACKNOWLEDGMENTS
 
Appreciation is extended to Fulbright South Africa and the North West Provincial Department of Agriculture for allowing the first author an opportunity to study in the USA. Partial support of the study was from the Institute of International Education (IIE). Work was funded through the Missouri Agricultural Experiment Station project number MO-NRSL0117 and the University of Missouri Center for Agroforestry under cooperative agreements 58-6227-1-004 with the USDA-ARS and C R 826704-01-2 with the USEPA. The results presented are the sole responsibility of the authors and/or the University of Missouri and may not represent the policies or positions of the USEPA. Any opinions, findings, conclusions or recommendations expressed in this publication are those of the authors and do not necessarily reflect the view of the USDA. Appreciation is extended to Randall Smoot at the Greenley Research Center for continual maintenance of the watershed site.


   NOTES
TOP
 NOTES
ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Contribution from the Center for Agroforestry, the Missouri Agricultural Experiment Station, and the Institute of International Education.

Received for publication August 20, 2004.


   REFERENCES
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 




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R. P. Udawatta, S. H. Anderson, C. J. Gantzer, and H. E. Garrett
Agroforestry and Grass Buffer Influence on Macropore Characteristics: A Computed Tomography Analysis
Soil Sci. Soc. Am. J., August 22, 2006; 70(5): 1763 - 1773.
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L. R. Ahuja, L. Ma, and D. J. Timlin
Trans-Disciplinary Soil Physics Research Critical to Synthesis and Modeling of Agricultural Systems
Soil Sci. Soc. Am. J., February 2, 2006; 70(2): 311 - 326.
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Journal of Natural Resources
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