Use of Herbaceous Legumes for Improving Soil Fertility and Crop Yield in Maize Cassava Cropping Systems

ABSTRACT This study evaluates the effects of harvest frequency and stage of development of annual and perennial forage legumes on biomass and nutrient accumulation of legume residue, rate of nutrient release from legume residue, availability of residue-derived nutrients to maize and/or cassava and soil water availability during the cropping season. Agronomic experiments were planted at Kenya Agricultural Institute (KARI), Mtwapa. The experimental design was split-plot, where the main plots were planting in pure stand of legume, maize and cassava and their combinations. The subplots were legume harvesting management: clitoria (Clitoria ternaea) cut at 2 months and then after 6 or 10 weeks, and dolichos (Dolichos purpureus) cut at 2 or 4 months after planting (MAP). The control plots were with or without inorganic fertiliser. The legumes exhibited different growth rates. During the Long Rain (LR) season when clitoria was establishing, intercropping maize with clitoria led to 27% more maize grain yield than maize without organic or inorganic fertiliser input. The reverse was true during the Short Rain (SR) season, when the presence of already well-established clitoria reduced maize grain production by 78%, such that the cumulative maize grain produced from the 2 seasons was 30% lower than that from the no-input control. The high green manure production of dolichos during the LR season led to high plant nutrient supply, 106 and 253 kg/ha for 2 and 4 MAP, respectively. The shading effect by dolichos on maize and cassava reduced the LR season maize grain yield by 27 and 49% when cut at 2 and 4 MAP, respectively. Fresh tuber yield of cassava was also reduced by 50% when dolichos harvest was delayed to 4 MAP. However, during the SR season when moisture was limiting, the nutrients were available to the maize crop, such that the cumulative maize grain yield from the 2 seasons was 37% higher than that from the no input maize pure stand control. Compared to the no-input control, fresh cassava tuber yield at 10 MAP was not affected by the presence of clitoria or dolichos harvested at 2 MAP. The soil inorganic N was abundant in the topsoil (0–20 cm) compared to the subsoil (20–40 cm) depth. These results indicate that the legumes, and the foliage harvesting management strategy influenced the maize grain and cassava production and the soil inorganic N content.