Effect of date of transplanting and nitrogen on productivity and profitability of rice–ratoon (Oryza sativa) system under shallow lowland

A field experiment was carried out during the boro season of 2014–15 to 2015–16 at the research farm, Gerua, Kamrup, Asom, to identify optimum planting date for main rice (Oryza sativa L.) and nitrogen level for ratoon rice under shallow lowland ecosystem. The experiment was laid out in a split-plot design with 3 replications. Three planting dates (5^th, 15^th and 25^th February) were assigned to main plots for main crop and 3 nitrogen levels (0, 20 and 40 kg/ha N) to subplots for ratoon crop. Naveen, a high-yielding variety of rice was taken as test crop. Results revealed that 15^th February planting proved significantly more productive and profitable for main rice (6.04 t/ha) as well as ratoon (2.33 t/ha) than those of 5^th and 25^th February planting. It was mainly owing to higher values obtained for growth and yield attributes like plant height, dry-matter accumulation, tillers/m², filled grains/panicle, panicle weight and length for main rice as well as ratoon crop from 15^th February planting. Hills/m², filled grains/panicle and fertility percentage of ratoon crop were significantly influenced by planting dates. Grain yield of main rice was highly correlated with number of panicles/m², spikelets/panicle and filled grains/panicle. However, grain yield of ratoon crop was significantly correlated with hills/m², number of panicles/m², spikelets/panicle, filled grains/panicle and fertility percentage. Nitrogen levels of 20 and 40 kg/ha resulted in significantly higher hills/m², panicles/m² and spikelets/panicle which resulted significantly higher grain and straw yields of ratoon rice over the control but remained statistically at par with each other. Thus, 20 kg/ha N application was enough to get good rice ratoon crop and additional income of 26,415/ha with benefit: cost ratio 3.36.