Saturday, 15 July 2006

Dynamics of Nitrogen, Phosphorus and Potassium Availability in Soils Amended with Banana-Trash Compost.

Venecio U. Ultra Jr.1, Danilo A. Mendoza2, and Angelina Briones2. (1) Univ of Eastern Philippines, University Town, Catararman, N. Samar, Philippines, (2) Univ of the Philippines Los Banos, College, Laguna, Philippines

In anticipation of the Philippines being a major producer of organic banana, this study was conducted to provide quantitative basis for certain practices in organic farming. The dynamics of N, P, and K availability in soils amended with various formulations of banana-trash compost were investigated in incubation studies. Changes in the chemical composition of ten formulations of banana trash-based compost involving leguminous plants (Sesbania rostrata, Flemingia macrophylla, Arachis hypogea) and chicken manure were analyzed periodically during a composting period of 16 weeks. Results 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 compost piles were characterized by increase in pH, total N and total P and decrease in total K, total carbon and C/N 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 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 compost formulations (BnT alone, BnT + Sesbania prunings, BnT + Flemengia prunings, BnT + Peanut stover and BnT + Chicken manure) and with uncomposted banana trash at 20t/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 in BnT treatments (uncomposted or composted) exhibits 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.

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