Title : Biological nitrogen fixation and yield of groundnut (Arachis hypogaea L.) in response to plant density, inorganic fertilizer and rhizobia seed inoculation
Abstract:
Plant density and nutrition are key factors affecting crop productivity. On-station experiments were conducted at two sites in Lilongwe, Malawi, during the 2019/20 and 2020/21 cropping seasons, evaluated the effects of plant density, rhizobia seed inoculation, and inorganic fertilizer on performance of groundnut varieties. Treatments included plant density (low-LPD; and high-HPD), groundnut varieties (Chitala -Spanish, and CG-9 -Virginia), application rates (0, 100 kg/ha) of D-compound fertilizer (NPK-8:18:15:6S+0.1B), and rhizobia seed inoculation (with/no inoculation). The experiment followed a factorial split-plot design with four replications. Both sites had low to medium levels of nitrogen and phosphorous, medium organic-matter. pH levels ranged from 5.1 to 5.7 at Chitedze and 5.1 to 6.3 at Horizon. Results showed that D-compound fertilizer increased nodule weight and BNF in both varieties, while inoculation increased nodule number per plant. Total N-fixed differed by variety, with CG9 fixing 41% more than Chitala, increase in N-fixation was also observed with D-compound fertilizer. In the second season, total N-fixed increased significantly with high plant density (p=0.017 and p<0.001), and fertilizer application (p=0.013 and 0.001). At Horizon, doubling PD increased BNF by 57% (CG9) and 75% (Chitala); at Chitedze by 46% and 105%, respectively. Over two seasons, HPD increased grain yield of CG9 and Chitala by 37-50% compared to LPD. Groundnut grain yield response to inoculation depended on fertilizer, increased yield due to inoculation were observed in absence of fertilizer. Proper soil fertility management should optimize plant density to enhance BNF and yield. In low nutrient conditions, LPD is preferable to HPD.
