Management of plant parasitic nematodes on sweet potatoes using biochar and chicken manure in Bungoma County, Kenya

Abstract

Sweet potato (Ipomoea batatas L.) is a source of food and nutrition in many developing nations. Plant Parasitic Nematodes (PPN) significantly reduce its productivity and yield. Synthetic nematicides used to manage PPN are harmful to the environment, non- target species and humans, and hence the need for safer and effective PPN management options. Thus, the aim of this study was to examine the effect of soil organic amendments on sweet potatoes and plant parasitic nematodes in Bungoma County, Kenya. The specific objectives were to: Assess the impact of drill and ridge farming systems on sweet potato yield; Evaluate the effect of biochar and chicken manure on sweet potato growth and yield; and Determine the effect of biochar and chicken manure on plant parasitic nematode abundance and diversity. A total of eleven treatments consisting of sole and combined soil amendment treatments of biochar and chicken manure were tested on sweet potatoes planted under drill and ridge farming systems on three farms (Ben, Mabanga and Nafula) using a completely randomized design and randomized complete block design in the first and second planting seasons, respectively. Data on plant biomass and yield that included total tuber weight and number, and marketable and non-marketable tuber weight and number were collected at harvest time, while the initial and final population density of PPN in the soil and on plant roots was collected at planting and harvest time, respectively. Data was analyzed using one-way analysis of variance and significant means separated using Tukey test in the R software. Results from each farm showed no significant yield differences (P=0.05) among treatments tested on sweet potatoes planted under drill farming. However, treatments tested under ridge farming produced significantly higher (P≤0.05) total tuber weight when compared to those under the drill farming, indicating that ridges ensured that the sweet potato roots had enough space to grow and develop. While biochar treatment increased plant biomass, co-application of biochar and chicken manure (five tonnes each) and the sole application of ten tonnes of chicken manure significantly increased (P≤0.05) total and marketable tuber weight, which is attributed to the nutrient-rich water released as a result of the decomposition of chicken manure. Economically significant PPN of sweet potatoes belonging to the genera Pratylenchus, Meloidogyne and Rotylenchulus were more prevalent in the soil than roots. Mabanga farm had significantly higher (P≤0.05) population density of PPN than Ben and Nafula farms. Co-applications of biochar and chicken manure significantly decreased (P≤0.05) the population size of PPN on all farms, but their impact on the different PPN genera was varied. Ridge farming with organic amendments, offers a sustainable strategy for sweet potato production. This study recommends field co-applications of biochar and chicken manure mixture (five tonnes each) under the ridge farming system as practical strategies to boost yield and reduce plant parasitic nematode pressure in sweet potato production.