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
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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.
