EVALUATION OF LEGUMES AS COMPONENTS OF INTEGRATED SOIL NUTRIENT MANAGEMENT FOR KALE PRODUCTION

Abstract

Declining soil fertility as a result of nutrient depletion is a major constraint to crop production in smallholder farms in northwestern Kenya. The use of legumes could play an important role in improving soil productivity of these production systems. Sunhemp (Crotolaria juncea L.) locally known as mito and mucuna [Mucuna pruriens var. Utilis (L) DC] were evaluated for soil fertility improvements as preceding rotation crops for subsequent kales (Brassica oleracea var. acephala) when herbage above 10 cm was removed as vegetable or feed. Eight treatments were evaluated using a randomized complete block design replicated five times in two seasons. The treatments were: (1) defoliated sunhemp, (2) defoliated mucuna, (3) defoliated sunhemp + 5 t/ha farm yard manure (FYM), (4) defoliated sunhemp + 30 kg/ha P₂O₅ + 30 kg/ha N, (5) defoliated mucuna + 5 t/ha FYM, (6) defoliated mucuna + 30 kg/ha P₂O₅ + 30 kg/ha N ha, (7) 60 kg/ha P₂O₅ + 60 kg/ha N and (8) No fertilizer (control). Legume dry matter yields and fresh kale leaf yields were measured. Sunhemp yielded greater (P<0.01) lower canopy stem stubble than mucuna. There were no significant differences (P>0.05) in herbage removed as food or feed, which ranged from 2.2 to 3.4 t/ha. The combination of stubble legume residue and either FYM or inorganic fertilizer yielded greater (P<0.05) kale leaf than no fertilizer control. The yields under the combination of stubble legume residue and half the recommended inorganic fertilizer were not significantly different (P>0.50) from those for recommended inorganic fertilizer. The remaining stubble legume residue after defoliating top canopy herbage as food or fodder can substitute for 30 kg/ha P₂O₅ + 30 kg/ha N. Despite the greater stubble residue incorporated under the sunhemp treatments, kale yields under mucuna treatments were similar to those from sunhemp treatments, suggesting that nutrient use by succeeding kale was enhanced under mucuna treatments. Farmers preferred the combination of legume stubble with FYM because it was associated with larger kale leaf, low cost of production and good persistence of the kales.