Submitted to: Agroforestry Systems
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/16/2011
Publication Date: 2/3/2011
Citation: Kremer, R.J., Kussman, R.D. 2011. Soil quality in a pecan – Kura clover alley cropping system in the midwestern USA. Agroforestry Systems. 83(2):213-223. Interpretive Summary: Soil conservation and soil quality maintenance are important considerations during the establishment and early growth of tree crops. Tree plantations or orchards are often established using an agroforestry practice, which is a multiple cropping system that involves simultaneous production of tree and agricultural crops. The type of management used in cropping the alleys between tree rows is critical because many agricultural practices may affect several soil properties that contribute to overall soil quality. Thus, soil disturbance associated with tillage within alleys of agroforestry systems could lead to erosion and degradation of soil quality. A recently established pecan orchard on fertile, wind-deposited (loess) soils of a hilly landscape bordering the Missouri River that was intercropped with a perennial legume (kura clover) was assessed for selected soil quality properties. The site was previously used to grow corn and soybeans followed by hay and pasture when pecans were planted in rows and kura clover was seeded in the alleys. Soils were collected according to landscape position during 2002 through 2009 for analyses of carbon (C) and nitrogen (N), soil aggregation, and for biological processes involved in cycling of C and N in the soil environment. Soil organic C (the main component of soil organic matter necessary for multiple functions in soil); aggregate stability, necessary for reducing erosion and enhancing water infiltration; and soil shear strength, a measure of resistance to erosion, increased in the kura clover alleys regardless of landscape position (summit, shoulder, or backslope) within eight years after establishment. Microbial enzyme activities, representing soil biological processes, also greatly increased in the in the kura clover alleys by the eighth year. All soil quality measurements were higher than those obtained from annually cropped field and unmanaged grass reference sites near the pecan agroforestry system. Also, kura clover did not interfere with growth of the young pecan trees and has been harvested for haylage (forage for cattle) since 2003 thereby providing a source of income until trees begin producing nuts. The results suggest that the pecan-kura clover agroforestry system has improved overall soil quality and, because tillage was avoided with the perennial stand of kura clover, soil conservation improved since conversion of the site from annual cropping and hay systems. Farmers, extension personnel, state and federal conservation agencies, and other scientists will find the research results applicable because they illustrate how tree crops intercropped with perennial forage or cover crops in an agroforestry system can not only improve soil properties on soils vulnerable to erosion but also provide economic benefits until the tree crop develops harvestable yields.
Technical Abstract: Intercropping alleys in agroforestry provides an income source until the tree crop produces harvestable yields. However, cultivation of annual crops decreases soil organic matter and increases soil erosion potential, especially on sloping landscapes. Perennial crops maintain a continuous soil cover, increase water infiltration, reduce soil erosion, and improve overall soil quality. The objective of this on-farm study was to assess the effects of a perennial legume, kura clover (Trifolium ambiguum M. Bieb.), on soil quality in a recently established pecan (Carya illinoinensis Wangenh. C. Koch) orchard. The pecan-kura clover agroforestry practice was established on deep loess soils of the Missouri River hills landscape. These silt loams are on 2 to 20 percent slopes and can be highly erosive. Kura clover, introduced as the alley crop five years after pecan planting, was selected based on its perennial growth habit, nitrogen-fixing ability, winter hardiness, high forage quality, and soil conservation properties. Kura clover was seeded in 2001 and harvested for hay annually beginning 2003. Soil organic matter and activities of selected soil enzymes increased compared with cultivated and grass pasture control soils by the eighth year of establishment. Water-stable aggregation improved by 50 percent and surface soil shear strength improved significantly (P < 0.05) in alleys compared with control sites. Results illustrate that kura clover as the alley-cropped component improved soil fertility and biological activity through increased organic matter and improved soil structure, and yielded high quality forage valuable for the cattle-feeding operation. Kura clover maintained or improved soil quality, reduced potential soil erosion, and benefited pecan growth by providing a source of soil nitrogen and improving soil structure for adequate water infiltration and aeration.