Use of inoculants to improve soyabean yield and Biological Nitrogen Fixation in Malawi

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Soyabean is an important crop in the farming systems in Malawi, particularly as a source of cash and proteins. In addition, soyabean has the potential to replenish soil nitrogen (N) through biological nitrogen fixation (BNF). The N fixed by soyabean can also be utilized by the component crop when used as an intercrop or in crop rotation. However, the potential benefits of soyabean in smallholder farming system are often not realised because of poor agricultural practices.

In the 2011/2012 season, N2Africa worked with farmers in Dedza, Lilongwe and Salima districts of Malawi. In those three agro-ecological zones, on-farm trials were implemented to determine the response of soyabean to inoculation. Six soyabean varieties – Solitera, Makwacha, Nasoko Soprano, Tikolore, and PAN 1867 – were evaluated in soyabean variety trials. In addition, Makwacha was evaluated in soyabean input trials. Biomass and grain yields were used to assess the performance of soyabean in heterogeneous environments as well as to evaluate the response to inoculation with rhizobium. In the trials Biofix legume inoculant, manufactured by MEA Ltd. under licence from University of Nairobi, Kenya, was used.

Our results demonstrated the consistent positive effect of using soyabean inoculant on both soyabean grain and biomass yield across the test sites. Inoculation of soyabean significantly increased grain yield by 53%, from 1317 to 2019 kg/ha for non-inoculated and inoculated soyabean respectively. However, the response to inoculation varied across the different soyabean varieties used, with PAN 1867 producing the largest mean grain yield. In the soyabean input trials, inoculation increased mean yield of Makwacha by 52.5% from 1431 to 2168kg/ha. Our results suggest that if the use of inoculants is promoted and subsequently adopted by farmers, we should be able to raise national production figures of soyabean by at least 50%, hence making a big impact on smallholder farmers producing soyabean and other players in the soyabean value chain.

The results also showed that Inoculation increases biomass yield. On average for all the six varieties, there was a biomass yield increase of 13% (from 2348 to 2661 kg/ha). For Makwacha in the soyabean input trials there was even a 20% biomass yield increase (from 2095 to 2520 kg/ha). This implies that when the biomass is incorporated back into the soil and when soyabean only fixes N from the atmosphere and does not take N from the soil, farmers should be able to replenish on average 13% more N into the soil when they would use inoculants than when they would not use inoculants. Analysis of N-content in the sampled soyabean biomass and soil N balance after a soyabean crop are yet to be completed and these will help to quantify soyabean potential in BNF.

The current orientation of N2Africa in Malawi is to determine the most practical and ideal storage and handling procedures for the inoculants, to engage and provide technical backstopping to agro-dealers and commercial seed companies importing and distributing the inoculants and to build capacity amongst farmers on the use of inoculants and field management in general. Strategies are being made on the use of vouchers to incorporate inoculants on soyabean seed sales and within the Malawi Government Targeted Input Subsidy Programme.

Chataika B., C. Banda and G. Kasongo