The use of organic and geological materials for soil fertility mainenance in the Southern highlands of Tanzania
Kamasho, J.A|Mayona, C.M|Rees, DJ / 1992

Over 40% of smallholder farmers use organic materials for soil improvement but currently only very broad, imprecise advice is available to guide them. Large yield responses have been observed when organic manures have been applied, and the application of organic manure has increased the response to inorganic fertilizer. Placement of organic manure below the seed gave much larger yield increases than broadcasting or incorporation the manure into the soil. The equivalence between organic and inorganic fertilizers varies with season and sire, but a conservative approximation is that one tonne of organic manure gives yield increases equivalent to 15-20 kg inorganic nitrogen in maize, and equivalent to 5-10 kg inorganic nitrogen in Phaseolus beans, for mid-altitude areas. It is estimated that the use of up to 20 t ha~1 organic manure is economically justified in maize production and up to 10 t ha-' in beans, provided it can be obtained and applied at a cost between 2000-5000 TSh a tonne, for the mid to high altitude areas.