Impact of Soil Fertility Management Practices on a Major Insect Pest Infestation and Yield of Beans (Phaseolus Vulgaris l.) in Taita District, Kenya

Abstract

The common bean is an important food and cash crop in Eastern, Central and Southern Africa. It provides food for more than 100 million people and is a critical source of income for rural households. Common bean yields, however, have declined in the last ten years. This decline is the result of poor soil fertility and nutrient depletion as well as high incidences of insect pests, key among them being the bean stem maggot (BSM). To address soil nutrient depletion and the accompanying declining agricultural productivity, integrated soil fertility management (ISFM) has been adapted as a framework for enhancing crop productivity through combining fertilizer use with other soil fertility management technologies, adapted to local conditions. The current study evaluated the influence of soil fertility treatments on yield and yield components of the common bean. Additionally, to establish the potential links between soil fertility and crop protection, the effect of ISFM interventions on the incidence of the BSM was also assessed. The experiment was carried out in Taita District where agriculture contributes 95% to household income with very little or no fertility inputs in farms. Bean variety Mwezi moja was sown during the wet cropping season. Farm plots were amended with Mavuno fertilizer (a blend of fertilizer containing 11 nutrients); Triple Superphosphate fertilizer with Calcium Ammonium Nitrate (TSP + CAN); cow manure; Trichoderma inoculant; Trichoderma inoculant with cow manure combination; Mavuno fertilizer with Trichoderma inoculants combination; and control (untreated check). Field survey was conducted four weeks after bean emergence to determine the incidence and prevalence of the BSM. Plant survival: dry-seed and and bean straw weight were used as criteria for assessing crop yield. Yield and yield components of common bean were significantly affected by addition of soil ammendments, with Mavuno fertilizer + Trichoderma inoculant improving yield by 52.9%. However, the influence of the soil ammendments on the BSM incidence was minimal. These findings point to the fact that soil fertility management interventions increase crop yield. Nevertheless, to maximise yield, there is a strong need to adopt agroecological strategies that not only optimise soil fertilization but also incorporate a pest management dimension.

Key words: Bean, Soil fertility, Beanfly, Yield