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

Published online May 6, 2005 Influence of Grass and Agroforestry Buffer Strips on Soil Hydraulic Properties for an Albaqualf Tshepiso Seobi, S. H. Anderson,* R. P. Udawatta, and C. J. Gantzer ABSTRACT tem is more effective if tillage and planting are performed Agroforestry production systems have been introduced in temper- along the contour. Schwab et al. (1993) estimated soil ate regions to improve water quality and diversify farm income. Agro- loss with the universal soil loss equation to be as low as Ϫ1 Ϫ1 forestry and grass–legume buffer effects on soil hydraulic properties 5.1 Mg ha yr for strip cropping, which was compara- for a Putnam soil (fine, smectitic, mesic Vertic Albaqualf) were evalu- ble with soil loss with terraces. Grass buffer strips reduce ated in a corn (Zea mays L.)–soybean [Glycine max (L.) Merr.] water- runoff and increase infiltration upslope from the strips; shed in northeastern Missouri. The no-till management watershed Schmitt et al. (1999) observed that doubling the width was established in 1991 with agroforestry buffers implemented in 1997. of a 7.5-m-wide grass strip doubled water infiltration into Agroforestry buffers, 4.5 m wide and 36.5 m apart, consist of redtop the soil. A multispecies riparian buffer increased the infil- (Agrostis gigantea Roth), brome (Bromus spp.), and birdsfoot trefoil tration rate five times compared with cultivated and (Lotus corniculatus L.) with pin oak (Quercus palustris Muenchh.), swamp white oak (Q. bicolor Willd.), and bur oak (Q. macrocarpa grazed fields (Bharati et al., 2002). The infiltration rates for components of the riparian buffer were as follows: Michx.) trees. Soil cores (7.6 cm in diam. by 7.6 cm long) were collected Ͼ from the treatments from four 10-cm depth increments to determine silver maple (Acer saccharum Marsh.) smooth brome saturated hydraulic conductivity (Ksat), soil water retention, pore-size (Bromus inermis Leyss), timothy (Phleum pretense L.), distributions, and bulk density. Bulk density was 2.3% lower (P Ͻ and Kentucky bluegrass (Poa pratensis L.) grass filter Ͼ 0.05) within the grass and agroforestry buffers compared with the row switchgrass (Panicum virgatum L.). They showed that crop areas. Total porosity and coarse mesoporosity (60- to 1000-␮m planting buffers can improve infiltration within 8 to diam.) were 3 and 33% higher (P Ͻ 0.05), respectively, for the grass 10 yr. Other studies also have demonstrated that peren- and agroforestry buffer treatments than the row crop treatment. The Ͻ nial vegetation can increase infiltration (Broersma et al., Ksat was three and 14 times higher (P 0.05) in the grass and agrofores- 1995; Wood, 1977). try buffer treatments compared with the row crop treatment. Results show that the grass and agroforestry buffer treatments increased po- Recently, a study was conducted to evaluate the ef- tential water storage by 0.90 cm and 1.1 cm per 30-cm depth compared fects of grass and agroforestry contour buffer strips on with the row crop treatment. Although the claypan horizon will domi- runoff, sediment, and nutrient losses on a claypan soil nate the surface hydrology, buffers may provide some benefit by re- (Udawatta et al., 2002). They found that these buffers ducing runoff from row crop management. 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 agro- xcessive surface water runoff is a principal cause forestry strips reduced runoff, total P and total N, al- Eof erosion and nonpoint-source pollution. Land though the agroforestry buffer strips failed to signifi- with steep slopes under row crop management has been cantly reduce sedimentation. Grass and agroforestry managed with terraces and surface water drainage sys- strips reduced water runoff by about 9%. tems to protect soil from erosion (Schwab et al., 1993). Soil properties are very important in selecting soil However, construction of terraces and drains is expen- conservation systems. Soil type and texture greatly influ- sive and only economical for higher-value crops (Coun- ence soil water movement and storage (Klute and Dirk- tryman and Murrow, 2000). sen, 1986). Claypan soils have a shallow topsoil layer, Contour strip cropping has been identified as a crop- usually a silt loam texture, with sufficient water transmis- ping system that reduces runoff velocity and soil loss sion pores. However, this surface horizon is underlain by (Martin et al., 1976; Schwab et al., 1993). Strip cropping a high clay content subsoil horizon (Blanco-Canqui et al., uses strips of row crops having a wide row spacing alter- 2002; Crockroft and Olsson, 1997; Motavalli et al., 2003; nating with crops having a narrow row spacing. This sys- 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 Tshepiso Seobi, North West Provincial Dep. of Agriculture, Soil Sci- and Donald, 1997) runoff. Blanco-Canqui et al. (2002) ence Section, Private Bag X804, Botha Street, Potchefstroom, South studied Ksat throughout the profile of a claypan soil. They Africa 2520; S.H. Anderson and C.J. Gantzer, Dep. of Soil, Environ- Ϫ1 mental and Atmospheric Sciences, 302 Anheuser-Busch Natural Re- found Ksat to be very low (0.002 mm h ) within the sources Building, and R.P. Udawatta, Center for Agroforestry, 203 claypan subsoil horizons relative to surface horizons Anheuser-Busch Natural Resources Building, Univ. of Missouri, Co- (70 mm hϪ1) for these soils, which increases runoff and lumbia, MO 65211. Contribution from the Center for Agroforestry, subsequent soil loss. the Missouri Agricultural Experiment Station, and the Institute of Inter- national Education. Received 20 Aug. 2004. Soil & Water Management Little is known comparing the impacts of grass and agro- & Conservation. *Corresponding author ([email protected]). forestry buffer strip practices on hydraulic properties Reproduced from Soil Science Society of America Journal. Published by America. All copyrights reserved. for claypan soils. The purpose of this study was to evalu- Published in Soil Sci. Soc. Am. J. 69:893–901 (2005). ate the effects of grass and agroforestry buffers on soil doi:10.2136/sssaj2004.0280 © Soil Science Society of America 677 S. Segoe Rd., Madison, WI 53711 USA Abbreviations: Ksat, saturated hydraulic conductivity; pHw, water pH. 893 894 SOIL SCI. SOC. AM. J., VOL. 69, MAY–JUNE 2005 respectively; yield data were not available for 1991. Runoff water quality is being monitored to determine nutrient, herbicide, and sediment losses from the watershed. 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 Put- nam 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 (Uda- watta et al., 2002). Restrictive claypans produce surface runoff during high rainfall periods in combination with periods of Fig. 1. Topographic map of study site with 0.5-m elevation interval lower evapotranspiration during the winter, spring, and early contour lines (thin black lines), agroforestry buffer strips (wide summer. The experimental site for this study was conducted gray lines), and sampling region (superimposed box). A grass water- only on the Putnam silt loam. way is located at the outflow end of the watershed (wider gray line; Soil samples from six profiles from the watershed were modified from Udawatta et al., 2002). The inset map shows loca- analyzed by horizon in 2000. Clay content, silt content, cation tion of watershed in Missouri. exchange capacity, organic C, and water pH (pHw) data for the upper soil horizons of the agroforestry watershed are pre- sented in Table 1. In the study area, the claypan on the average hydraulic properties for a claypan soil at a watershed occurred at about the 38 cm depth. study site in northeastern Missouri (Udawatta et al., 2002). The objective of the study was to measure and com- Sampling Procedures pare soil water retention, pore-size distributions, bulk Undisturbed soil cores, 7.6 cm in diam. and 7.6 cm in length, density, and Ksat for grass buffer, agroforestry buffer, and row crop treatments. 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 MATERIALS AND METHODS treatments (Fig. 1). Experimental Site Soils from the second and the third contour buffer strips counting from the southern edge of the watershed were sam- The experimental watershed used for this study is located pled for the agroforestry and grass buffer treatments.

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