Legume and Organic Fertilizer Effects on Soil Nutrient Availability, Uptake and Kale Yields in Kabete Sub-county Kenya

Declining soil fertility is the main constraint to kale (Brassica oleracea var. acephala) a common vegetable, production in parts of Kiambu County Kenya. A field experiments to evaluate the effect of legume integration and application of organic fertilizers on soil N and P (and OC), uptake and kale yield was set up in Kabete field station of the University of Nairobi, in the long and short rainy season of 2014. The experimental layout was a Randomized Complete Block Design with a split plot arrangement. The main plots were; (i) sole kale, (ii) kale intercropped with lupin and chickpea (lupin/kale and chickpea/kale) and (iii) Kale succeeding lupin and chickpea (lupin-kale and chickpea-kale). The spilt plots were the organic fertilizers inputs; Minjingu rock phosphate (MRP) and Farm yard manure (FYM), and the control. the nutrients N, P and organic carbon, kale N, P uptake and yield were analyzed at intervals of 1, 2 and 3 months of kale development. The plant available N was higher in the lupin/kale intercrops + FYM in both seasons. Plant available P was significantly (P≤0.05) higher in lupin/kale intercrop + MRP across the two seasons. There were no significant changes in soil organic carbon levels with legume integration and organic fertilizers application throughout the sampling period in both short rain seasons. In both seasons, significant higher N concentration was obtained in a sole kale + FYM whereas P concentration was significantly increased in a lupin/kale intercrop + MRP. Lupin/kale intercrop + FYM and lupin/kale intercrop +MRP showed a positive correlation (R2=0.99) between soil N and plant N, soil P and plant P respectively in both seasons. Higher kale yields were obtained in lupin-kale rotation + FYM and MRP; chickpea-kale rotation + FYM and MRP and kale monocrop + FYM. Integration of white lupin (intercrop/rotation) + FYM and MRP in a kale production system leads to a significant improvement on soil nutrient status, kale nutrient uptake and yield. Similarly where lupin was integrated positive correlations of soil and plant N and P were recorded and this means that the nutrient supplied was able to replenish the soil as much as plant took them up.