Soil management drivers of common beans (Phaseolus vulgaris) yields

Abstract

In the face of low and declining common bean yields in Uganda, past research has focused on crop improvement and crop protection against pest and diseases. Little has been done to understand the limitations from soil factors due to the widely held opinion that they are leguminous and can fix their own nitrogen to overcome challenges from low soil fertility. A survey was conducted on 25 bean farmer gardens in Kitooke village, Gayaza sub county Kyankwanzi district. The specific objectives of this study therefore were to assess the variation in soil chemical properties (available P total N, exchangeable bases and soil pH) across bean field types and assess the variation in bean yield across bean field types in Kitooke village, Kyankwanzi District. Soil samples were collected. The soil samples were analyzed for total N, available P, exchangeable K, Na and Ca, OM, pH and Texture using standard laboratory procedures. The bean fields were monitored to enumerate the growing conditions of the crop. Four quadrats were established diagonally in each garden to estimate the total plant population. The total number of plants were counted and recorded per quadrant. In each quadrat, three plants were selected randomly during harvest and number of pods and number of seeds per pod were counted, weighed on a sensitive digital scale and data recorded separately. Soil analysis data were subjected to correlation analysis to identify uncorrelated soil properties, which were then subjected to principal component analysis and hierarchical clustering to generate a dendogram whose clusters were used to test the hypothesis about effect of soil properties on bean yields in Kyankwanzi District. PC1 accounted for 36.7% while PC2 accounted for 33.2% of the observed variation of the surveyed bean fields the loadings of the PC1 showed that exchangeable potassium and total nitrogen were the most influential soil characteristics explaining the variability in surveyed bean fields, which were grouped into 2 clusters in the dendogram based on the selected soil characteristics. Cluster 1 had more fertile soils with respect to K and N compared to Cluster 2. Cluster 1 had higher bean yield than cluster 2 by 170kg per ha. This difference was due to higher number of pods per plant and higher seed yield per plant in Cluster 1 compared to Cluster 2. It was concluded that higher soil fertility can enhance common bean yield in Kitooke village, Kyankwanzi village, despite the common notion that being leguminous, common beans can fix their own N and therefore perform well on low fertility soils. It was recommended that nutrient omission trials be conducted in the study area to identify and quantify the inherent soil supply of the most limiting nutrient to common bean production. Keywords: Available phosphorus, Exchangeable potassium, Soil pH, Total nitrogen, Uganda.