Ameliorating acid infertile rice soil with organic residue from nitrogen fixing trees

Residues from two nitrogen fixing trees, Albizia zygia and Gliricidia sepiu m and one non nitrogen fixing tree Samania dinklagei and their combination with 50% of rice husk, were evaluated for their effect on growth and yield of rice (Oryza sativa) varieties (Rok 10 and Rok 23) grown in an Oxisol col lected from a rice paddy in Inland valley swamps of Sierra Leone, West Afri ca. Ground and dried residues were mixed with soil and labelled with N-15 a mmonium sulfate (9.855% atom excess) at a rate of 10 mg N kg(-1) soil. The P-32 isotopic exchange method was used to determine the effect of organic r esidue incorporation on the bioavailable soil P status at five levels of P application. Albizia zygia and G. sepium had higher quality leaf litter (wi th relatively lower C/N, lignin/N and cellulose/N ratios) whereas Semania d inklagei and rice husk had high carbon, lignin and polyphenolic contents. A pplication of organic residue had positive effects on the soil available P status at varying degrees. Higher adsorption capacity, kinetic value and me an solution time of phosphates in solution were obtained with the A. zygia, and G. sepium residues. These values were lower with rice husk and S. dink lagei Gliricidia sepium and A. zygia contributed more nitrogen derived from organic residue than rice husk and S. dinklagei but the mixture of A. zygi a and G. sepium with rice husk enhanced N utilization.