Submitted to: Communications in Soil Science and Plant Analysis
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/16/2005
Publication Date: 8/31/2006
Citation: Mungai, N.W., Motavalli, P.P., Kremer, R.J. 2006. Soil organic carbon and nitrogen fractions in temperate alley cropping systems. Communications in Soil Science and Plant Analysis. 37:977-992. Interpretive Summary: Increasing public concerns over the environmental effects of global warming have stimulated an interest in land use practices, such as agroforestry, which may promote trapping of carbon (sequestration of soil organic carbon [C]) and reduce emission of carbon dioxide into the atmosphere. Agroforestry is a multiple cropping land use system that involves simultaneous production of tree and agricultural crops. Information is limited on how soil organic C and nitrogen (N) is distributed and accumulated in long-term agroforestry systems. Nitrogen is essential for both plant nutrition and soil microbial activity, in which N aids in releasing C from organic substances including plant litter. We examined the variability in distribution of soil organic C and N relative to tree rows in established agroforestry plantations in north central Missouri during 2001 and 2002. Soils were collected from tree rows and the between-row spaces (alleys) for analyses of C and N in the soil environment. The two sites were a 19-year old pecan orchard with bluegrass planted in the alleys (Pecan site), and an 11-year old silver maple planting with soybeans and corn planted in the alleys in alternate years (Maple site). Soil C and N contents were higher in the tree rows than in the middle of the cropped alleys at both sites. The results suggest that the type of leaf litter (crop residues vs tree litter) returned to the soil strongly influences biological cycling and the location within the production site for storage of soil C and N. Farmers, extension personnel, state and federal conservation agencies, and other scientists will find the research results applicable because they illustrate that different combinations of trees and agronomic crops considered for agroforestry may require different management practices to gain the most benefit from soil N and that carbon dynamics (extent of sequestration in soil) may vary as well.
Technical Abstract: Alley cropping may promote greater sequestration of soil organic carbon. The objective of this study was to examine spatial variability of soil organic C and N fractions relative to tree rows in established alley cropping systems in north central Missouri. Soils were collected to a depth of 30 cm from two alley-cropped sites, a 19-year old pecan(Carya illinoinensis)/bluegrass (Poa trivialis) intercrop (Pecan site) and an 11-year old silver maple (Acer saccharinum) /soybean (Glycine max)-maize (Zea mays) rotation (Maple site). Particulate organic matter (POM) C constituted 15-65% and 14-41% of total organic C (TOC) at the Pecan and Maple sites, respectively, whereas POM N comprised of 3 to 26% of total N (TKN). TOC and TKN were on average 13% and 18% higher at the tree row than at the middle of the alley for surface soils (0-10 cm) at the Pecan site, respectively. Similarly, POM C was two to three times higher at the tree row than the alley at the Maple site. No differences in microbial biomass C and N between tree row or alley positions were observed. Observed results suggest the existence of spatially dependent patterns for POM C, TOC, and TKN, relative to tree rows in alley cropping.