Sole maize and intercropped maize-bean crops were studied over four seasons from 1996-1998. Addition of inorganic P at the rate of 60 kg P2O5 ha-1 only slightly increased maize yields particularly in monocultures. Cattle manure, added at 12 t ha-1, had no effect on maize grain yields during the first season, possibly due to short-term nutrient immobilisation induced by the high C:N ratio of the manure. In subsequent seasons, use of cattle manure slightly increased maize grain yields in both the monocultures and polycultures. Symbiotic N2 fixation by the intercropped beans was evaluated using the natural 15N abundance method. Intercropping increased the proportion of N2 fixed in beans on average from 55% to 69%. Intercropping thus provides a strategy for a better N resource use where the maize crop competes efficiently for available soil mineral N and the legume replenishes part of the extracted N via atmospheric N2 fixation. However, the amounts of N2 fixed appear not to be enough to replenish all of the systems' N exports in grain crops and, therefore, additional N inputs are needed. Consequently, more attention needs to be given to manure management and its long-term impact on soil fertility and crop yields.

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0103|AL-Maize Program|AGRIS 0102|AJ

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