Effect of Mucuna Fallow on Succeeding Maize Nutrition and Yield in Farmer-managed On-farm Trials
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On 18 farmer-managed fields in the Forest-Savannah Transitional zone of Ghana, the response of unfertilized maize was investigated as influenced by either a previous short season natural fallow or Mucuna pruriens (L.) DC var. utilis (Wright) Burck. Comparative vector diagnosis of three weeks old seedlings revealed that N was limiting maize growth. The previous Mucuna fallow was at least partly able to compensate N while there was a dilution of all the other macronutrients due to an increased uptake in the Mucuna system. Maize yields were on average 51% higher after Mucuna fallow with 2850 kg ha(-1) compared with 1880 kg ha(-1) after natural fallow, but the variability between farmers' fields was high. Adaptability analysis revealed that the slash-and-mulch leguminous fallow system was most effective at locations of high productivity while the yield difference to the slash-and-burn natural fallow system was small in farming environments with low productivity. It was concluded that M. pruriens var. utilis fallow is not a suitable technology to reclaim degraded land or to restore soil fertility if growth-limiting factors are not eliminated. Low available P levels and later maize planting significantly reduced the yield difference and hence the risk for M. pruriens to be outperformed by the natural fallow system increased up to 41% with lower values of plant available P and later maize planting. Besides individual yield components such as cob number and cob seed weight, plant population at final harvest accounted for 58% of the variation in yield. Nutrient use efficiency improved significantly for all macronutrients except P but the harvest index was significantly lower at 0.40 after Mucuna fallow compared with 0.43 after natural fallow. N supplied by the Mucuna fallow supported a better growth of the succeeding maize crop but only in the beginning of the cropping season. When the yield level a farmer usually experiences with his common practice on a specific field was applied to the regression models of the adaptability analysis it was possible to make site-specific yield predictions for the M. pruriens system. It was concluded that the application of the adaptability analysis and individual risk assessments might serve as valuable tools to give more site-specific recommendations to farmers instead of blanket messages for entire regions.
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