Litter quality effects on soil carbon and nitrogen dynamics in temperate alley cropping systems

Microcosm and litterbag experiments were conducted to determine the effects of litter quality, soil properties and microclimate differences on soil carbon (C) and nitrogen (N) mineralization in alley cropping systems. Bulk soils were collected from 0 to 20 cm depth at three sites: a 21-year old pecan (Carya illinoinensis)/bluegrass (Poa trivialis) intercrop (Pecan site) in north-central Missouri, a 12-year old silver maple (Acer saccharinum)/soybean (Glycine max)–maize (Zea mays) rotation (Maple site) in northeastern Missouri and a restored prairie site (MDC site) in southwestern Missouri. Seven tree and crop litters with varying composition were collected, including pecan, silver maple, chestnut and walnut leaf litter (tree litter) and maize, soybean and bluegrass residues (crop litter). Aerobic microcosm incubations were maintained at 25 °C and a soil water potential of ?47 kPa. Unamended MDC soil mineralized 24 and 18% more CO₂ than the Pecan and Maple soils, respectively. Soil amended with crop litter mineralized on average 32% more CO₂ than when amended with tree litter. Net N mineralization from soybean litter was 40 mg kg^?1, while all other litter immobilized N for various durations. A double pool and a single pool model best described C and N mineralization from amended soils, respectively. Cumulative CO₂ mineralized, labile C fraction (C₁) and potentially mineralizable C (C₀) were correlated to litter total N and lignin contents and to (lignin + polyphenol):N ratio. In the field, bluegrass litter decomposed and released N twice as fast as pecan leaf litter. Soybean, maize and silver maple litter released 84, 75 and 63% of initial N, respectively, 308 days after field placement, while no differences in mass loss was observed among the three litter materials. At the Maple site, mass and N remaining, 308 days after field placement was lower at the middle of the alley, corresponding to higher soil temperature and water content. No differences in mass loss and N release patterns were observed at the Pecan site. Microclimate and litter quality effects can lead to differences in nutrient availability in alley cropping systems.