Exploring options to enhance biological nitrogen fixation and yield of soyabean and common bean in smallholder farming systems in Rwanda

After my last PhD updates, a paper was published in the N2Africa Special Issue of Agriculture, Ecosystems and Environment as Rurangwa, E., Vanlauwe, B., Giller, K.E., 2018. Benefits of inoculation, P fertilizer and manure on yields of common bean and soyabean also increase yield of subsequent maize. Agric. Ecosyst. Env. 261, 219-229. https://www.sciencedirect.com/science/article/pii/S0167880917303651.

Figure.1. Climbing bean grown: (A) with no inputs added, and (B) with inputs added at Muko village

Figure 2. Climbing bean grain yields as affected by inputs at Kinoni and Muko villages; Control: no inputs added

Here I present grain yield (Fig. 2) of climbing bean from a paper I am currently working on. In Rwanda the cultivation of climbing bean is increasing especially in the highlands of the Northern Province. Although this area has favourable conditions for the cultivation of climbing bean, very high population density has resulted in small landholdings which are repeatedly cropped with little or no fertilizer, and smallholder farmers in the area achieve poor yields. Climbing beans provide cover during the growing season and valuable residues for livestock feed. Improved cover of climbing beans helps in suppressing weed growth as well as reducing water and soil loss from the steep slopes observed in the Eastern African highlands.

Field experiments were conducted in farmers’ fields in Muko and Kinoni villages in the Northern Province of Rwanda. Fields in Muko were identified as high potential and those in Kinoni as low potential in terms of soil fertility. We evaluated the effect of mineral N, P and K fertilizers (both alone and in combination) and manure on the productivity of climbing bean in the two villages (seven fields in each). The results showed that application of fertilizer and / or manure significantly (P<0.001) increased the grain yields at both sites (Fig. 2). Kinoni site had significantly (P<0.001) smaller grain yield than Muko site. Average grain yield was 2.8 t ha-1 and 4.1 t ha-1 for Kinoni and Muko respectively. Application of fertilizer inputs led to greater yields in all fields of the study sites. From this study it is clear that the influence of management overrides and farmers in the area are advised to prioritise agronomic management if they are to benefit from their tiny lands (Fig. 1 & 2).

Edouard Rurangwa, Rwanda Agricultural Board (RAB), Rwanda and Wageningen University & Research, the Netherlands (For his 2017 update click here)

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