Synchronizing legume residue nutrient release with Kale (Brassica oleracea var. acephala) uptake in a Nitrosol of Kabete, Kenya

Nitrogen (N) and phosphorus (P) are identified as major limiting nutrients for many cropping systems (Kwambiah et al., 2003) and their application from organic and inorganic sources is essential to maximize and sustain crop yield potentials (Hartermink et al., 2000). N is commonly considered a key factor limiting crop growth in organic systems (Möller et al., 2008) and, unlike conventional farming systems, rely on management of soil organic matter to optimize crop production (Watson et al., 2002). Addition of plant residues, quantity wise and timing, has thus become a pivotal strategy in soil fertility improvement for crop production e.g. kales (Brassica oleracea var. acephala) under organic farming systems. Chickpea (Cicer arietinum) and white lupin (Lupinus albus L.) are leguminous crops commonly intercropped with kales (Genga, 2014) and their influence on crop yield and soil nutrient status has been widely studied (Nduku 2014, Genga 2014; Onwonga et al., 2015). There is however a dearth of information with respect to synchronization of nutrient released by legume residues with pattern of nutrient uptake by kales to match their demand. The objective of the current study was therefore to assess decomposition and nutrient release rates of chickpea and lupin residues and kale nutrient uptake patterns for better synchrony of nutrient supply and demand.