Dynamics of nitrogen, phosphorus and potassium availability in soils amended with banana-trash compost

Results of the study showed that combinations of banana trash (BnT) and chicken manure or leguminous plants were highly decomposed compared to untreated BnT. The use of Bioquick as composting inoculant combined with leguminous materials enhanced decomposition. The composts piles were characterized by increase in pH, total N and total P and decreased in total K, total carbon and C/P ratio with time. Notably, BnT + chicken manure attained C/N ratio of 15 at 4 weeks while the BnT + leguminous materials reached such low C/N ratio at 8 to 16 weeks. Incubation study was conducted under greenhouse conditions for 24 weeks. It was designed to follow the dynamics of N, P and K availability in three clay soils (Antipolo, Binangonan and Lipa) amended with five composts formulations (BnT alone, BnT + Sesbania prunings, BnT + Flemingia prunings, BnT + Peanut stover and BnT + chicken manure) and with uncomposted banana trash at 20 t/ha application rate. Results showed that net N mineralization occurred in soils amended with BnT + chicken manure and BnT + leguminous materials which had C/N ratios ranging from 11.83 to 15.60. Net N immobilization during the earlier period of incubation was observed in uncomposted and composted banana trash with C/N ratio of 68.17 and 23.92, respectively. Significant net P mineralization was obtained only in soils amended with BnT + chicken manure. Abrupt increase in exchangeable K was observed in all treatments two weeks after the incorporation of organic residues. Higher available K and BnT treatments (Uncomposted or composted) exhibited the inherently high K content of banana residues. The kinetics of N and P mineralization conformed to the first order mineralization models for treatments showing no net immobilization. Magnitudes of mineralizable N pool (No) and mineralizable P pool (Po) are dependent on the N and P content of compost materials added to the soil. Decomposition rates (K) increased with increase in Po but no defined relation occurred between K and No. Available K in BnT amended soil also conformed to first order kinetics. The equations are useful in predicting the amounts of potentially available nutrients in soils amended with banana trash-based composts under optimum conditions. Overall, results of the experiments provided quantitative measure of the N, P and K supplying potential of compost-amended soils