Effect of Biochar and Vermicompost in the Suppression of Plant Parasitic Nematodes Affecting Beans (Phaseolus vulgaris L.) in Western Kenya.

Plant parasitic nematodes are a major threat to common bean production in Western Kenya, causing up to 60% yield losses, with root-knot nematodes (Meloidogyne spp.) being the most devastating. Bean is the most widely cultivated food legume in the tropics and subtropics and is the main source of protein in the diet. Bean is highly susceptible to root-knot nematodes and other plant parasitic nematodes with minimal chances of resistance. Nematodes interact with other soil-borne pathogens causing disease complexes that are a major constraint in bean production due to the associated losses and increased costs of their management. Field trials were conducted in 48 small-holder farmer’s fields in Western Kenya in four agroecological zones during the long and short rain seasons of 2013 and 2014. Organic amendments which comprised of biochar and vermicompost were incorporated into the soil via furrow application to determine their potential in managing nematodes during the long rain seasons and their residual effect over the short rain seasons. Two bush type cultivars, Rosecoco GLP 2 and KK15 were used for this study. Gall scoring was conducted and plant roots with galling symptoms were collected for isolation and extraction of nematodes. Reductions in the galling index on bean roots and increased yield were observed where amendments were applied, compared to the control plots. Fifteen different genera of plant parasitic nematodes and 21 different genera of free-living, non-parasitic nematodes were enumerated. Meloidogyne spp. was the most abundant of the plant parasitic nematodes enumerated. Nematode trapping fungi were present and correlated with decreased nematode abundance at 15 sites. The use of organic amendments will offer the bean farming community a nematode management option that is affordable, environmentally friendly, with long-term sustainable benefits in terms of improved soil health and increased bean productivity.