PLANT RESIDUE DECOMPOSITION AND NITROGEN DYNAMICS IN AN ALLYE CROPPING AND AN ANNUAL LEGUME-BASED CROPPING SYSTEM

Field experiments were conducted to compare plant residue decompositio n and nitrogen (N) dynamics in an alley cropping system (AC) and an an nual legume-based cropping system (NA) in the Piedmont region of Georg ia, USA. The hedgerows of the alley cropping system consisted of Albiz ia julibrissin (albizia) established in January 1990. Hedges were four meters apart with a spacing within rows of one-half meter. A rotation beginning with Mucuna deeringiana (velvet bean) followed by a winter annual crop of Trifolium incarnatum L. (crimson clover), a summer crop of Sorghum bicolor (L.) Moench (grain sorghum) and a winter crop of T riticum aestivum L. (wheat) was established in the alley cropping syst em and a control annual cropping system. All crops were grown using no -tillage systems. Plant residue decomposition and N dynamics were meas ured using litterbag technologies on crimson clover, albizia, and grai n sorghum. Soil and plant total N, decay rate constants (k) for dry ma tter, soil potentially mineralizable N, and nitrification rates were d etermined. Decay rate constants for N were best correlated with the li gnin content of the plant residues. No residue quality parameter was s ignificantly correlated with decay rate for dry matter. There was no s ignificant difference between AC and NA systems in soil inorganic N an d potentially mineralizable N; however, nitrification rates were great er in the AC. Grain sorghum N uptake and biomass production were not d ifferent for AC and NA. This was thought to be due to large inputs of organic N prior to the start of the experiment.