Participatory Evaluation of Spacing and Intercropping on Productivity of Bambara Groundnuts and Sorghum in Embu County, Kenya.

Abstract

Bambara groundnut (Vigna subterranea L. Verdc) is underutilised in Kenya, and little is known on its best agronomic practices in various agroecological zones. The objective of this study was to determine the influence of spacing and intercropping on the productivity of Bambara groundnut and sorghum in Embu County using a farmer-participatory approach. Two separate experiments were conducted in three sites in Mbeere North, Mbeere South and Embu West, sub-counties of Embu County. The experimental design was a randomized complete block design replicated thrice in each site. The experiments were conducted in two seasons: during the short rains (October – December 2019) and long rains (March-May 2020). The first experiment was to determine the optimum spacing of Bambara groundnut, where the main plot treatments were three landraces, namely BG 001, BG 003 and BG 005. The treatments were three population densities: S1 = 50 cm x 20 cm, S2 = 50 cm x 30 cm, S3 = 50 cm x 40 cm. Data was taken on Bambara plant spread, leaf area index, number of branches per plant, the weight of grains per plant, number of pods per plant, length of pods, number of seeds per pod, 100 grain mass, and total dry weight land equivalent ratio. The second experiment assessed the effect of intercropping of Bambara groundnuts with sorghum on sorghum productivity. The treatments included T1 -monocrop sorghum spaced at 60 cm x 20 cm, T2 - monocrop Bambara groundnut spaced at 50 cm x 20 cm, T3 - sorghum with one row of Bambara groundnut intercrop 120 cm x 15 cm with legume residues removed after harvest and T4 - Sorghum with one row of Bambara groundnut intercrop 120 cm x 15 cm with legume residues incorporated into the soil. Local farmers were involved in data collection through organized farmers’ field schools to enable them to make informed adoption decisions. The participants were sampled using a multistage spatially stratified random sampling design. Sorghum data was taken: panicle length, weight, 100 grain mass and total yield per plant. The third study assessed the smallholder farmers' willingness to adopt the best agronomic practices of Bambara groundnut; the study involved 384 small-scale farmers sampled from the farmers’ field school participants from the three sites. The respondents were interviewed using a structured questionnaire. The agronomic data from the first and second experiments was subjected to a three-way analysis of variance, and treatment means were separated using Tukey’s Honestly Significant Difference at 95% confidence level. The socioeconomic data was subjected to descriptive statistics, including means, frequencies and percentages, using SPSS. The study concluded that spacing of 50 cm x 20 cm was optimum with the highest yield of 6.02 ton ha-1 among the three landraces of Bambara groundnut tested with landrace BG 001 recording the highest total grain yields of 4.49 ton ha-1. Intercropping sorghum with Bambara groundnut residues removed and intercropping sorghum with Bambara groundnut residues incorporated into the soil recorded land equivalent ratio greater than 1, indicating yield advantage over sorghum and Bambara groundnut monocrops which recorded land equivalent ratio less than 1. The proportion of farmers who showed willingness to adopt the best agronomic practices of Bambara groundnut production was 60.94%. The study recommended growing landrace BG 001 of Bambara groundnut at a spacing of 50 cm x 20 cm in the study area and other areas with similar agroecology. The study recommends intercropping sorghum between two rows of Bambara groundnuts since it resulted in higher sorghum yields with 3.74 mg ha-1.