Effect of varying levels of nitrogen on production, economics and energy-use efficiency of direct-seeded rice (Oryza sativa) genotypes under upland rainfed ecosystem of Bihar

A field investigation was conducted during the rainy seasons of 2016 and 2017 on clay-loam soil of upland rainfed ecosystem of Bihar, to evaluate the performance of 7 rice (Oryza sativa L.) genotypes (Swarna Shreya, IR 84899-B-179-13-1-1- 1, IR 83929-B-B-291-2-1-1- 2, IR 84887-B-158-7-1-1- 4, IR 84899-B-183-20-1-1- 1, IR 84894-143-CRA-17- 1 and Rajendra Bhagwati) under 4 levels of nitrogen application, i.e. control, 50% recommended dose of nitrogen (RDN, 60 kg N/ha), RDN (120 kg N/ha) and 150% RDN (180 kg N/ha). Results revealed that increasing levels of nitrogen increased yield attributes and economics of direct-seeded rice genotypes. Among the nitrogen levels significantly higher grain yields (2.90 t/ha) and net returns (27×10³/ha) were recorded with application of 180 kg N/ha. Application of 150% RDN increased the grain yield by 84.7% over the control and 43.6% over the RDN. Crop productivity (25.7 kg/ha/day), dry-matter efficiency (67.5 kg/ha/day) and economic efficiency (236/ha/day) were also higher with 180 kg N/ha. Among genotypes, significantly higher grain yield and net returns were shown by 'Swarna Shreya' (2.54 t/ha and 44.6x10³/ha, respectively) but it was on a par with 'IR 84899-B-179-13-1-1- 1′ (2.43 t/ha and 43 x 10³/ha) and 'IR 83929-B-B-291-2-1-1- 2′ (2.41 t/ha and 42.3 x 10³/ha). Crop productivity (22.1 kg/ha/day), dry-matter efficiency (64 kg/ha/day) and economic efficiency (204 ha/day) were higher with 'Swarna Shreya'. Carbohydrate-equivalent yields (2.27 t/ha) and carbon output (3.40 t CO₂ eq./ha) were significantly higher with application of 180 kg N/ha. Across the genotypes, 'Swarna Shreya' had significantly higher carbohydrate-equivalent yields (1.99 t/ha) and carbon output (3.25 t CO₂ eq./ha), but statistically similar to IR 84899-B-179-13-1-1- 1 and IR 83929-B-B-291-2-1-1- 2. Gross energy output (102.4 x 10³MJ/ha), net energy returns (74.2 × 10³MJ/ha), energy intensity in physical terms (3.68 MJ/kg), energy intensity in economic terms (4.48 MJ/) and energy-output efficiency (844 MJ/ha/day) were higher with 180 kg N/ha. However, energy profitability and energy productivity showed higher with preceding levels of N. ‘Swarna Shreya’ had higher gross energy output (97.3 × 10³ MJ/ha), net energy output (74.7 × 10³ MJ/ha), energy ratio (4.31), energy profitability (3.31), energy productivity (0.327 kg/MJ/ha), energy intensity in physical terms (3.11MJ/kg), energy intensity in economic terms (4.55 MJ/) and energy output efficiency (844 MJ/ha/day). Thus, growing of Swarna Shreya and advanced breeding line IR 84899-B-179-13-1-1- 1′ along with application of 180 kg N/ha is an ideal approach to achieve the optimum crop productivity, monetary returns and energy-use efficiency of direct-seeded rice under the upland rainfed agro-ecosystem of Bihar.