Effectiveness of White Lupin (Lupinus albus) and Chickpea (Cicer arietinum ) in Enhancing Phosphorus Release from Rock Phosphate

Smallholder farming systems are characterised by application of suboptimal rates or non utilisation of inorganic fertilisers due to their exorbitant prices vis-à-vis low financial return from crops. Minjingu rock phosphate (MPR) would be a viable option to the expensive inorganic phosphorus (P) fertilisers but is insoluble. The use of white lupin and chickpea, apart from fixing N, can enhance the solubility of rock phosphate through the release of carboxylic acids. The objective of the study is to increase P release from MPR and soil available N content using white lupin (Lupinus albus L. cv. Amiga) and chickpea (Cicer arietinum L). The study will be carried out at Egerton University Research Field (Field 7) and University of Nairobi Kabete Farm. The experimental design will be a randomised complete block design with a split plot arrangement. The main treatment will be cropping system (monocropping, intercropping and crop rotation) while sub-plot treatments P source (TSP and MPR). Maize and sorghum will be the test crops. Green house experiments with varying rates of MPR (0, 30, 60, 60 kg P ha-1) under lupin or chickpea will also be established. P and N contents in soil and plant tissues will be measured at different growth stages. Additionally, P and N balances in soil, pH and organic C will be measured. It is hypothesized that growth of white lupin and chickpea in rotation or as an intercrop with the application of MPR will lead to increased soil available P and N with resultant high maize and sorghum yields.