Soil litter dynamics and N use in a leucaena (Leucaena leucocephalaLam. (de Witt)) alley cropping system in southwestern Nigeria

The recovery of a single application of leucaena (Leucaena leucocephala) leaf N (78 kg N ha−1) in a maize crop, the hedgerow and the top 10 cm soil of a leucaena alley cropping system was measured for 236 d through the use of 15N labeled residues. The leucaena-derived-N (LDN) was followed in the surface litter and the soil-litter — separated by a flotation method on water — during the same period.At 45 and 129 d after the residue application (DAA), only 4.2 and 10.0% of the added leucaena N was recovered in the maize crop while the aboveground hedgerow incorporated 9.6 and 9.4% in its first and second canopy regrowth. At 45 and 129 DAA, 19.7 and 13.2% remained in the surface litter and soil. Total recoveries were 33.5 and 42.2% on the respective dates. The C and N content of the coarse (larger than 2 mm) and fine (between 2 and 0.25 mm) soil-litter fraction of the top 5 cm layer strongly increased after residue application. Soil total C in the total soil-litter decreased from 22% at 45 DAA to 8% at 236 DAA. A significant positive relationship (1% level) was found between the microbial biomass C and the total soil-litter C. The LDN release rate from the combined surface litter-coarse soil-litter was 0.0477 d−1, while the fine soil-litter had a LDN release rate of 0.0083 d−1. Only 8.6% of the released surface litter-coarse soil-litter LDN entered the fine soil-litter pool. These turnover rates lead to a poor synchronization of the LDN released from all litter pools with the maize LDN uptake during the first 45 d of maize growth, while between day 45 and 129, all released LDN was recovered either in the soil, maize or hedgerow