Cowpea growth in relation to Nutrient accumulation and distribution
The effect of different sampling dates on dry matter production grain yield and mineral distribution and accumulation in two cowpea varieties, 'Katuli 107' and 'MM4' were studied in a deep sandy loam soil of Murinduko, sub-station of Embu Agricultural Research Station. Results from this study indicated that there were varietal differences in dry matter production and grain yield. Katuli maintained superiority in these two parameters over 'MM4'. Grain yield in Katuli was attributed to the. high number of pods per plant and higher number of seeds per pod. High dry matter production in 'Katuli '107' was mainly attributed to the leaves which accounted for over 60% of the total dry matter in most of the sampling periods. The concentration of N, P, K, Ca, Mg and S showed significant changes in the various sampling times in the two varieties. Except for P, the period of active accumulation of these mineral nutrients occurred between flowering and mid-pod fill (5-8 weeks after emergence). Phosphorus active accumulation occurred between seedling and flowering. 'Katuli 107' accumulated more of these nutrients than 'MM4' except for sulphur. The results also indicated that the leaves accumulated the highest amount of the mineral nutrients. At mid pod fill the leaves contained 60-70%, stems contained 20-25% and roots contained 7-12% of the total nutrient content in the plant in both varieties. This high nutrient content in the leaves decreased for most nutrients after mid pod fill. This decrease suggested a mobilization phenomenon of nutrients from the leaves to the developing seeds. The results also showed that cowpea varieties which have ability to accumulate more nutrients produce higher dry matter and grain yields.