Hf. Schnier et al., TOWARDS A PRACTICAL APPROACH TO FERTILIZER RECOMMENDATIONS FOR FOOD CROP PRODUCTION IN SMALLHOLDER FARMS IN KENYA, Nutrient cycling in agroecosystems, 47(3), 1997, pp. 213-226
A comprehensive long-term fertilizer trial programme for annual crops
was established in 1985 at 70 sites in the high and medium rainfall ar
eas of Kenya testing N and P, farmyard manure and other critical nutri
ents. Sites were selected according to their representativeness regard
ing soils and climate in agro-ecological units. The fertilizer trial p
rogramme included all major food crops typical for the respective area
, both monocropped and intercropped in the case of cereals. Economic o
ptimum fertilizer rates were calculated taking into account input/outp
ut price ratios and value-cost ratios. The majority of sites showed re
sponses to N or P, only at one site response to both N and P with a si
gnificant interaction was found. Price elasticity of crops such as pot
atoes and cabbages was higher than that of maize or sorghum. Critical
soil P levels were determined for maize at 13 ppm P for modified Olsen
extract and 32 ppm P for Mehlich I extract. Variability of rainfall w
as found to greatly influence viability of fertilizer recommendations.
First attempts to extrapolate fertilizer recommendations from areas o
f representativeness to areas with similar conditions by means of GIS
and modelling approaches are discussed.