ENHANCING SOIL NITROGEN THROUGH CROP ARRANGEMENTS AND FERTILIZER: A COMPARATIVE ANALYSIS OF MBILI INTERCROPPING AND CONVENTIONAL METHODS FOR SUSTAINABLE MAIZE- SOY BEAN FARMING IN WESTERN KENYA

Abstract

Low fertility in highly weathered and degraded soils largely accounts for low and unsustainable crop yields in most African countries. Nitrogen (N) is the most deficient among other nutrients because other than being required in large quantities, is and very susceptible to leaching losses. The study assesses soil N replenishment technologies' impact on adoption rates, yields, and economic benefits of maize-soy bean cropping systems in western Kenya. A baseline survey was conducted on adoption levels of the existing soil N replenishment technologies in three farmer associations (FAs) in June 2011. Management of Beneficial Interaction of Legume Intercrops (MBILI), Mono, and conventional cropping systems’ effects was evaluated on soil N content. In conventional cropping system, Maize (IR) was planted at 75 cm row spacing and 30 cm in-row spacing with soy bean seed planted between the maize at 10 cm spacing. Imazapyr Resistant (IR) maize and soy bean were used as the test crops. The experiment was a split-plot design with two factors (cropping systems as the main factor and fertilizer interventions as the sub factor) arranged in a randomized complete block design (RCBD) with three replications. During the short rains of 2011, (Farm yard manure) FYM (0.965% N) was sourced from the University of Eldoret farm. An application of 75 kg N/ha led to 7.8t /ha of manure. In the long rains and short rains in 2012, FYM from the farmers with 0.39%, 0.73%, and 0.85% N in Teso, Vihiga, and Bungoma counties respectively was applied at 75 kg N/ha. The initial soil characterization results showed that soil cation exchange capacity (CEC) was largest in Vihiga (9.88 cmolc/ kg), Bungoma (5.38 cmolc/ kg) but relatively low in Teso (1.78 cmolc/ kg). In 2011, short rains season, soil Nitrate-N levels were significantly the largest in the fourth week after planting (1.95 mg/kg soil). Maize mono, MBILI and soya mono all had significantly larger Nitrate-N than soils in which a conventional cropping system was practiced. However, in 2012 the long rains season, Nitrate-N, was the largest in preseason (2.62 mg/kg) which decreased to 0.56 mg/kg during 4WAP, before rising to 0.74 mg/kg and 1.49 mg/kg during the eighth and twelfth weeks after planting, respectively. Whereas the cropping system had no significant influence on Nitrate-N, the application of FYM 75 kg N/ha produced a significantly (p<0.05) larger soil Nitrate-N level (1.49 mg/kg) compared with Calcium Ammonium Nitrate (CAN) 30 and 75 kg N/ha at all sampling periods and depths. Maize planted with 75 kg N/ha application yielded 2.24 t/ha and 2.25 t/ha maize grain in FYM treatments, which were significantly larger than the 30 kg N/ha (or FYM 30kg N/ha which gave 1.53 t/ha and 1.64 t/ha respectively. Soy bean yields were significantly larger in the monocropping system compared to both MBILI and the conventional intercropping system. The mean Land Equivalent Ratio (LER) values were always > 1.0 for intercropping cropping system. In maize and soy bean, Nitrogen Use Efficiency (NUE) was largest in the mono-cropping system, followed by MBILI, and lastly, in conventional farming. The largest NUE was realized in FYM30N and CAN30N, whereas FYM75N and CAN75N were lower, suggesting increasing the N application reduces its use efficiency. High soil Nitrate-N was positively correlated (r = 0.430) with yields and NUE at 4WAP in 2011. The MBILI cropping system had the largest gross margin (Kshs 46 164/ha). The largest number of soy bean nodules was in FYM regardless of the application rate and lowest in CAN, implying that FYM is more efficacious in nodulation, especially when applied to nutrient-poor soils. From survey result, least used technologies were found to be Ua Kayongo (IR seed), MBILI intercropping, fortified compost, and use of Farm yard manure and liming. This informed the selection of technologies for this study. Findings from this study showed that MBILI cropping system planted at 30 kg N/ha optimizes crop yields, Nitrate-N utilization, nodulation and NUE, and gross margins.