G. Cadisch, E. Handayanto, C. Malama, F. Seyni, K.E. Giller
Nitrogen recovery from 15N-labelled prunings of Gliricidia sepium, Peltophorum dasyrrachis, Calliandra calothyrsus and Leucaena leucocephala, each of two different chemical qualities, was followed over three cropping cycles in a growth room. Half of the pots of each treatment received a further addition of unlabelled pruning material, from the same species as that previously applied, before the second and third crop cycle. The cumulative maize total N accumulation revealed the largest benefit from N rich, low lignin and polyphenols Gliricidia prunings followed by Leucaena, Calliandra and Peltophorum. Cumulative N recovery measured using 15N over the three crop cycles ranged from 9% from Calliandra prunings to 44% from Gliricidia prunings. The vast majority of this N was recovered during the first crop cycle which agreed well with estimates using the N difference method. Recoveries in the second and third crops ranged from 0.4-5% (15N method) and 6-14% (N difference method) of the N initially applied. The protein binding capacity of polyphenols was the best predictor of N recovery at both initial and later crop cycles. Treatments which led to a large N recovery initially, continued to provide greater N benefits in subsequent cycles although with increasing harvest time this trend decreased. Thus, there was no compensation in initial N release from low quality prunings at later harvests and the agronomic implications of this are discussed. Addition of unlabelled Gliricidia prunings before the second and third cycle led to a positive apparent priming effect on previously applied 15N labelled prunings. By contrast, repeated additions of Peltophorum residues, rich in lignin and active polyphenols, resulted in a reduced recovery of initially applied pruning-15N. However, the maximum positive or negative effects on recovery of pruning N amounted to less than 2% recovery of the initial amount of N added over 14 weeks. Thus the scope for regulation of N release from tree prunings during these later stages of decomposition appears to be limited.
Department of Biological Sciences, Wye College, University of London, Wye, Ashford, TN25 5AH, United Kingdom; Department of Soil Science, Faculty of Agriculture, Universitas Brawijaya, Malang 65145, Indonesia; Department of Ecological Research, INRAN, Niamey, BP429, Niger
