Response of maize in rotation with cowpea to NPK fertilizer in a low rainfall area
1990
Shumba, E.M. (Ministry of Lands, Agriculture and Rural Resettlement, Harare (Zimbabwe). Dept. of Research and Specialist Services)
The effect of NPK fertilizer on maize grain yield, economics of fertilizer use and changes in soil nitrogen and phosphate in maize-cowpea rotation was assessed at a low rainfall (450 to 650 mm) site over four seasons. There was a significant maize grain yield increase of 42 to 102 per cent at one-quarter the recommended NPK rate during the first three years and of 75 per cent at half the recommmended rate in the fourth season. Using a minimum acceptable marginal rate of return of 60 per cent, fertilizer use was economical in two of the four years. Inclusion of cowpea in the rotation increased soil nitrogen by 32 kg N/ha across fertilizer treatments between 1985/86 and 1988/89. Despite being persistently uneconomic and depressing yields in some years compared to lower NPK rates, the recommended rate of 135 N, 24P and 26K kg/ha raised soil phosphate by 31 kg P/ha after the third cropping season
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