Effects of Ground Rock Phosphate and Elemental S on Yield and P Uptake of Maize in Western Kenya

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Abstract
SUMMARY: The effect on maize yields of ground rock phosphate, alone or mixed with sulphur in either of two proportions, and of single-superphosphate, was measured at five consecutive harvests. At the first harvest single-superphosphate increased yield by 1.54 t and the best of the mixtures by 0.56 t grain/ha. Ground rock phosphate alone had no effect on yield. At the third harvest there were no yield differences between sources; because yields produced by rock phosphate and the mixtures improved. The cumulative increase in yield produced by single-superphosphate was 3.58 t/ha and by rock phosphate 2.69 t grain/ha, but because the fertilizer cost ratio was 3:1, additional grain produced by rock phosphate cost half as much. The apparent P recovery ranged from 5.40 to 8.28 kg/ha, with most from single-superphosphate and least from the mixture containing most elemental-S.

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