Differential use and benefits of Velvet bean (Mucuna pruriens var. utilis) and N fertilizers in maize production in contrasting agro-ecological zones of E. Uganda

Research was conducted in eastern Uganda on a transect from Mt. Elgon (high altitude) to the low-altitude zones. The aim of the study was to evaluate the use of Velvet bean (Mucuna pruriens var. utilis) and inorganic N fertilizer in improving maize production in contrasting agro-ecological zones over two seasons. The high and medium altitude zones are high-potential agricultural areas, with much more reliable rainfall and the opposite is true for the low-altitude zone. Each zone comprised soils of contrasting productivity levels.During 22 weeks, Mucuna produced 2.6–7.9 t ha−1 of dry matter, accumulating 80–200 kg N ha−1, and derived approximately 34–108 kg N ha−1 from the atmosphere. In the subsequent season, a maize crop was used to evaluate the effects of the green manure-N as compared to 40 and 80 kg N ha−1. The mean maize yield of the farmers’ practice was used to distinguish between high- and low-productive fields at each location.There was a significant increase in maize yield in response to the added N, both from urea or M. pruriens var. utilis’. The average increase above that of the farmers’ practice was 1.0 t ha−1 for the low-productivity fields across the agro-ecological zones, However, the above average fields responded to added N by a mere 0.4 t ha−1 in the low-productivity areas. In the high-productivity areas as much as 2.2 t ha−1 were gained. The aggregated maize yield increase over two seasons indicated an increment of 2.7 t ha−1 with the application of inorganic fertilizers, and of 1.9 t ha−1 with a preceding mucuna-maize relay on high productivity fields in high-potential agro-ecological zones, compared to 1.3 t ha−1 obtained with either strategy on the low-productivity fields across the agro-ecological zones.Economic benefits are obtained with any N supply strategy on highly productive fields in high-potential agro-ecological zones. The N supply strategies are as profitable as the farmers practice on the more productive fields in low-potential agro-ecological zones. However, farmers on low-productivity fields across the agro-ecological zones are currently operating in an economically downward spiral. Only the alternate use of a mucuna-maize relay provides them a way out of this predicament. Given the current prices for maize and urea, the adoption of fertilizer-N in any but the most favorable environment cannot be expected.