Nitrogen, Rhizobium and molybdenum for higher soil bacterial population, N uptake and productivity of lentil (Lens culinaris) grown under rice (Oryza sativa)-fallow conditions

Abstract

A field experiment was conducted during the winter (rabi) seasons of 2014–15, 2015–16 and 2016–17 in loamy soils of the Regional Agricultural Research Station, Assam Agricultural University, Shillongani, Assam, to study the effect of varying doses of nitrogen, Rhizobium and molybdenum on bacterial population in soil, N uptake, yield attributes, grain yield and economics of lentil (Lens culinaris Medikus spp. culinaris) grown after the harvesting of winter rice (Oryza sativa L.) variety ‘Gitesh’. Soil bacterial population increased with the increase in nitrogen doses. The crop grown using seeds inoculated with Rhizobium @ 50 g/kg seed and sodium molybdate @ 1 g/kg seed along with 100% of recommended dose (RD) of N (15 kg/ha) accrued in the highest bacterial population in the soil at harvesting. Seed inoculation with Rhizobium and sodium molybdate led to considerably higher bacterial population build up in soil than seed inoculation with Rhizobium and sodium molybdate separately. Nitrogen uptake by lentil got reduced with decreasing N doses, being 28.54 kg/ha under RD of N and 28.03 kg/ha under 75% of recommended N. The treatment combinations involving RD and 75% of RD of N (11.25 kg/ha) and seed inoculation with Rhizobium and sodium molybdate recorded 35.16 kg/ha and 34.97 kg/ha N uptake respectively. These 2 treatment combinations ultimately accrued in higher values for plant height, pods/plant, seeds/pod and 100-seed weight and significantly higher grain yield (928.90 and 868.89 kg/ha respectively) as compared to all other treatment combinations. Benefit: cost ratios under these 2 treatment combinations were 2.18 and 2.09 respectively. The treatment combinations were tested for maximizing lentil production utilizing rice-fallows and farmers’ acceptability in farmers’ fields during rabi 2017–18 through 3 Krishi Vigyan Kendras (KVK) in Upper Brahmaputra Valley (UBV) in Jorhat district, Central Brahmaputra Valley (CBV) in Nagaon district and Lower Brahmaputra Valley (LBV) in Nalbari district of the state. The RD of N + seed inoculation with Rhizobium and sodium molybdate yielded the highest (5.8–8.2 q/ha) at all the locations closely followed by 75% RD of N + Rhizobium + sodium molybdate (5.93–7.25 q/ha).