Influence of integrated soil nutrient management on cowpea root growth in the semi-arid Eastern Kenya

The effect of integrated soil fertility management (ISFM) on root growth of selected cowpea varieties in two sites with contrasting rainfall amounts over two seasons was investigated. Nine cowpea varieties were used as test crop and the treatments applied include a control, farmyard manure at 2.5 t ha(-1), triplesuperphosphate (TSP) at 15 kg ha(-1) as (P(2)O(5), 0:46:0), and TSP mixed with farmyard manure at the singly applied rates. The experiment was laid down as a split plot design and it was replicated three times. Data collected include root and shoot biomass at 50% flowering, and shoot biomass at crop maturity. In addition, root to shoot ratios at 50%, correlations between root biomass and shoot biomass at 50% flowering, and correlations between root biomass at 50% flowering and shoot biomass at crop maturity were also determined. The data were analysed as a split plot design using GenStat for Microsoft windows. Results obtained revealed that addition of nutrient inputs enhanced root biomass at Ndunguni during both the long and short rains and only in two treatments at Kavuthu during the short rains. However, addition of nutrients relatively lowered root: shoot ratios in most treatments in both study sites during the two seasons indicating phosphorus (P) deficiency in the study sites. Furthermore, strong positive and significant (p < 0.05) correlations between root and shoot biomass were recorded during the long rain season which was relatively dry compared to the short rain season, indicating the dependence of shoot growth on root growth under limiting moisture conditions. These results revealed the need to add nutrients, especially P, to enhance cowpea root growth and the importance of moisture in root and shoot growth in the drylands.