Effects of Intercropping Bambara Groundnut (Vigna subterranea (L) Verdic) and NERICA rice (Oryza sativa L.) on their Productivity and Soil Fertility

Abstract

Agricultural production in Kenya has stagnated since 1980s resulting in malnutrition in over 89% of Kenya's population. Food insecurity has been identified as the prime cause of malnutrition. Low agricultural productivity due to declining soil fertility resulting from poor cropping systems and use of non adapted exotic crop species has worsened this situation. Intercropping offers advantages if well planned including improved soil fertility and yields. Bambara groundnuts have shown high yield in low fertility soils and have been described as a complete food NERICA rice has been , reported to offer higher yields and shorter growing seasons. Cropping systems that combine both these crops in production systems will help alleviate malnutrition and food insecurity. The objectives of this study were to assess cropping systems and soil conservation strategies in production systems in Butere Division, Butere District, Western Kenya, evaluate the effect of Bambara groundnuts intercropped with NERICA rice on their growth and productivity, determine the effect of Bambara groundnuts intercropped with NERICA rice on their roots spatial distribution and resource mobilization and evaluate the effect of intercropping Bambara groundnuts and NERICA rice on soil fertility. A number of experiments were conducted including; field experiments at University. Botanic Garden, Maseno University, Butere Division, Western Kenya and at Hannover Germany. Greenhouse experiment was also conducted at University of Hannover, Germany. A transect walk across the Butere Division, Western Kenya was done to evaluate the soil conservation and soil fertility improvement methods used by the farmers. At University Botanic Garden, Maseno, seven treatments including Tl Sole crop of bambara groundnuts, T2 Rice NERICA 1 without intercropping with bambara groundnuts, T3 Rice NERICA 1 intercropped with bambara groundnuts, T4 Rice NERICA 4 without intercropping with bambara groundnuts, T5 Rice NERICA 4 intercropped with bambara groundnuts, T6 Rice NERICA 11 without intercropping with bambara groundnuts and T7 Rice NERICA 11 intercropped with bambara groundnuts were used. At Butere Division, the same treatments were used except NERICA 1 which was excluded. At Hannover field and greenhouse experiments, only NERICA 11 was used. During the greenhouse experiment to evaluate roots interactions, the NERICA rice and .bambara groundnuts were intercropped in partitioned and non partitioned root zones. The roots were later scanned and analyzed for interactions. Plant growth parameters and resources mobilization during the field experiments were evaluated. Photosynthetically active radiation was determined using the line quantum sensors both below the canopies of the two crops and above the canopy of bambara groundnuts. Soil analyses including nitrogen, phosphorous, pH and soil moisture were done to evaluate soil fertility variations in the course of the intercrop system The data from survey study was subjected to descriptive analyses. Data obtained from soil and plants measurements were subjected to analysis of variance (ANOVA) to determine if the treatment effects were significant at 5% level. Separation of means was done by Least Significant Difference (LSD) at 5% level. Over 50% of the respondents practiced intercropping during both short and long' rain seasons with maize/bambara intercrop system dominating the short rain season. Both agronomic and physical soil conservation measures are practiced in the Division. organic mulches, agro-forestry systems and grass barriers dominate the agronomic measures while water retention ditches, broad beds and fanya juu dominate the physical measures. The plant height ofNERICA rice was significantly (P:SO.05)increased when intercropped with bambara groundnuts but the plant height of bambara groundnuts was not significantly affected. The leaf area of intercropped NERICA rice and bambara groundnuts was significantly (P::;O.05) increased. Intercropping significantly influenced dry matter allocation in both crops. Intercropping of the two crops in one root zone significantly (P::;O.05)affected the roots interaction as well as dry matter allocation. Intercropping significantly increased the yield of both bambara and NERICA rice, v with delay in time to heading and flowering in NERICA. The PAR utilization was significantly increased under intercropping system as compared to sole cropping. Similar observations were made for soil nutrients analyses. Intercropping of bambara groundnuts and NERICA rice 4 and 11 resulted in better resources utilization and yield, though time to heading and flowering in NERICA was delayed while poding time was also delayed in bambara groundnuts. Intercropping enhanced roots interaction with bambara groundnuts roots penetrating deeper as compared to NERICA rice roots under intercropping system Soil fertility under intercropping system was maintained with bambara groundnuts replenishing the soil N through its association with N fixing bacteria. This study provides an understanding of the NERICA rice and bambara groundnuts interactions under intercrop system This allows us to understand the response mechanisms both below and above ground of the two crops to resources.