Submitted to: Biology and Fertility of Soils
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/15/2005
Publication Date: 12/30/2005
Citation: Mungai, N.W., Motavalli, P.P., Kremer, R.J., Nelson, K.A. 2005. Spatial variation of soil enzyme activities and microbial functional diversity in temperate alley cropping systems. Biology and Fertility of Soils 42(2):129-136. 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) 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 on how accumulation of soil organic C and N as soil organic matter in long-term agroforestry systems is limited. Because microbial activity is an indicator of organic matter levels in soil, we examined the variability in microbial processes involved in C and N cycling in the soil environment in established agroforestry plantations in north central Missouri during 2001 and 2002. The two sites were a 21-year old pecan orchard with bluegrass planted in the alleys (Pecan site), and an 12-year old silver maple planting with soybeans and corn planted in the alleys in alternate years (Maple site). Microbial enzyme activities and diversity of the soil bacterial communities were highest in the pecan tree rows compared to the middle of the cropped alleys. Only bacterial diversity differed within the Maple site. The results suggest that the type of tree leaf litter as well as the crop residues returned to the soil strongly influence microbial processes involved in nutrient cycling. Farmers, extension personnel, state and federal conservation agencies, and other scientists will find the research results applicable because they illustrate that levels of microbial activity differ under trees compared to the cropped alleys, which will require development of different long-term nutrient management strategies.
Technical Abstract: Spatially dependent patterns in microbial properties may exist in temperate alley cropping systems due to differences in litter quality and microclimate in areas under trees compared to those in the alleys. The effect of tree row location was evaluated for its impact on soil enzyme activities and substrate-use patterns. Soils were sampled to a depth of 30 cm at the tree row and at the middle of the alley at two sites: a 21-yr-old pecan (Carya illinoensis/ bluegrass (Poa trivials) intercrop (Pecan site) and a 12-yr-old silver maple (Acer saccharinum)/soybean (Glycine max)-maize (Zea mays) rotation (Maple site). Sites were sampled in fall 2001 and summer 2002. Beta-glucosidase activities, substrate-use patterns expressed as average well color (AWC) development, substrate richness and Shannon diversity index, and total Kjeldahl nitrogen (TKN) were significantly higher (P<0.05) in the tree row than at the middle of the alley for surface soils at the Pecan site. Fluorescein diacetate (FDA) hydrolytic activity was also higher at the tree row for soils sampled in the fall, but did not differ significantly for soils sampled in the summer. At the Maple site, AWC and substrate richness were significantly higher at the tree row for soils sampled in 2001. Soil volumetric water content and temperature were generally lower in the tree row at the Maple site. The results of this study suggest that functionally different microbial populations may be present under pecan trees compared to cropped alleys, which may promote disparities in nutrient availability and necessitate differential long-term nutrient management in such alley cropping systems.