Growth, nodulation and yield of selected legumes under drought conditions in Kitui county, Kenya

Abstract

Loss of fertility in soil is the main limiting factor that affects production of crops in Kenya, especially in the Arid and Semi-arid regions. In the lower parts of Eastern Kenya, unreliable and low rainfall has led to the low yields in crop production. Lack of the use of commercial fertilizers is also a contributing factor to low crop yields. Amongst new solutions that can assist farmers facing this challenge of low yields includes the emerged potential role of rhizobia in crop performance under water-scarce conditions. Therefore, this study focused on the analysis of drought affects nodule formation, growth, and yield. The analysis involved four legumes that are cultivated as a norm Arid and Semi-Arid Lands in Kitui County, Kenya. The legumes include; beans, cowpeas, Dolichos lablab, and green grams. The trials in the project lasted for two seasons and involved randomized complete block design with drought stress treatment (DST). DST had to be induced using withholding total irrigation, and a well-watered treatment (WWT) maintained to act as the control. Four blocks, each with four plots, were well divided. The four legumes were randomly placed in the plots and maintained under WWT. After a period of thirty days (a month), upon planting, the induction of DST followed which limited irrigation in of the two blocks. On the other hand, WWT was maintained in the other two blocks as controls. After the specified duration of the experiment, the roots for the legumes for both DST and WWT were harvested and analyzed. The root nodules were then taken to the laboratory for isolation of rhizobia and an inoculant preparation for specificity assays under greenhouse conditions. The results indicated that plants subjected to DST had less (p≤0.05), TND, NoP, lower LAI, more WIX, and lower GYD than control or plants under WWT. This implied that the widespread deleterious impact of water deficit on legume nodulation, growth, and yield. The reduced TND under DST could inhibit nitrogen fixation, further lessening GYD in legumes. Amongst the legumes, green grams had significantly higher (P≤0.05) GYD, TND, and least WIX, Dolichos lablab, and cowpeas showed a moderate performance of the three types traits. Beans showed the least TND, GYD, and high WIX under DST. Under DST, Green grams had a higher (p≤0.05) yield followed by Cowpeas, Dolichos, lablab, and Beans, significantly affected by water stress to give the lowest yield. Generally, TND positively correlated with GYD and negatively with wilting (WIX), potentially implying that higher nodulation might have enhanced nitrogen fixation, thus higher legume YLD and tolerance to water deficit. Based on observed performance, i.e., wilting index, root nodules number per plant, and grain yield, green grams were considered drought tolerant and beans drought susceptible. Therefore this study recommends the adoption and growth of green grams. In conclusion, the present study identified green grams (variety KS-20) as a high yielding and drought tolerant legume that could be adopted or promoted for sustainable food production in Kitui County. The rhizobium isolated from this green gram could also be cultured and potentially used as a bio-fertilizer to enhance yield in other Kenya's ASALs.