Exploring the nutrient release potential of organic materials as integrated soil fertility management components using SAFERNAC

Abstract

The aim of this study was to establish the nutrient release potential of different organic materials and assess their role in integrated soil fertility management for coffee using the new coffee yield model SAFERNAC. It involved an incubation experiment conducted at TaCRI Lyamungu Screenhouse for 180 days between April and September 2011. Cattle manure, coffee leaves, pulp and husks, Albizzia leaves and four green manure plants – Mucuna pruriens, Lupinus albus, Canavalia ensiformis and Crotalaria ochroleuca were mixed with two soil types – Eutric Nitisols from Lyamungu, Hai district and Humi-Umbric Acrisols from Yoghoi, Lushoto district. The mixing ratio was 5% organic to soil, the mixture was moistened to FC and incubated in 10 litre plastic containers arranged in RCBD (10 treatments and 3 replications) at room temperature. Duplicate soil samples + were taken at day 0, 3, 8, 15, 26, 45, 74, 112 and 180 and analyzed for NH 4 -N, NO 3 -N, available P and exchangeable K. The cumulative N min , P and K values resulting from the treatments were used to estimate their relative contribution to the soil nutrient pool and later exposed to the new model SAFERNAC for yield estimation under different nutrient management options (1 to 10 tons organics per ha alone on one hand and supplemented with 160 kg N, 60 kg P and 160 kg K). The tested organics differed significantly (P<0.001) in their N min, P and K release in the two soil types. They also differed in their substitution values and therefore the amounts of nutrients each one can contribute to the soil nutrient pools. Green manures showed about ten times higher potential as compared to cattle manure. Four of them (Crotalaria, Mucuna, Canavalia and Lupine) were picked as best bets for inclusion in the coffee ISFM programme. SAFERNAC recommended a number of nutrient management options involving the test organics and the two soil types under organic and conventional coffee farming.