Submitted to: North American Agroforestry Conference
Publication Type: Proceedings
Publication Acceptance Date: 5/15/2009
Publication Date: 6/1/2009
Citation: Kremer, R.J., Kussman, R. 2009. Soil Quality in a Pecan Agroforestry System is Improved with Intercropped Kura Clover. In: Gold, M.A., Hall, M.M., editors. Agroforestry Comes of Age: Putting Science into Practice. Proceedings of North American Agroforestry Conference, May 31-June 3, 2009, Columbia, Missouri. p. 373-358. 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 cropped to corn and soybeans until 1996 when pecans were planted in rows and kura clover was seeded in the alleys. Soils were collected according to landscape position during 2002 through 2006 for analyses of C and N, soil aggregation, and for biological processes involved in cycling of C and N in the soil environment. Soil organic carbon (the main component of soil organic matter necessary for multiple functions in soil) and aggregate stability, necessary for reducing erosion and enhancing water infiltration, steadily increased in the kura clover alleys regardless of landscape position (summit, shoulder, or backslope) during the four-year period. Microbial enzyme activities, representing soil biological processes, were also highest in the in the kura clover alleys. 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) or seed 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 an annual cropping system. 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 of agroforestry systems provides an income source until the tree crop produces harvestable yields. However, cultivation of annual crops decreases soil organic matter and increases soil erosion, especially on sloping landscapes. Perennial crops maintain a continuous soil cover, maximize water infiltration, minimize 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), on various soil quality parameters in a recently established pecan (Carya illinoinensis) orchard. The pecan-kura clover agroforestry system was established on deep loess soils of the Missouri River hills. These silt loams are on 3 to 10% slopes and can be highly erosive. Kura clover, intercropped eight 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 2002 and harvested for hay annually beginning in 2003. During this period soil organic matter and activities of selected soil enzymes have steadily increased compared with cultivated and grass pasture control soils. Water-stable aggregation improved by 50%. Results illustrate that kura clover as the interplanted 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. Pecan trees thrive in this system partly because soil quality is maintained or improved and, unlike other “living mulch” systems in which cover crops may suppress the main crop, kura clover does not compete with tree growth.