Influence of nitrogen application on wheat crop performance, soil properties, greenhouse gas emissions and carbon footprint in central Bhutan

In Bhutan, wheat (Triticum aestivum L.) is an important staple crop and its productivity is low due to poor soil fertility and inadequate external inputs. Hence, effects of four levels of nitrogen (N) [0, 50, 80 and 100 kg N ha−1] on wheat crop and soil properties were examined for two consecutive years (2012 and 2013) in a rice-wheat rotation. The experiment was set up in a randomized complete block design and the treatments replicated three times. In addition, greenhouse gas (GHG) emission was analyzed both per unit area and per kilogram of wheat grain to determine the emission-intense sources. Data were subjected to analysis of variance. Among the treatments, 100 kg N ha−1 had the largest effect on grain yield and dry biomass and on plant height. Significant correlations were detected for the N rates vs. dry biomass. However, correlations between N rates vs. soil N, C:N ratio and pH were significant for 2013 only. The average GHG emissions were 1114.2 kg CO2e ha−1 and 0.533 kg CO2e kg−1 grain and the emissions per hectare were highly influenced by N rates whereas the emissions per kilogram of grain were influenced by grain yield. We concluded that, in Bhutan, the application of N-fertilizer significantly enhanced wheat productivity and soil health at N rates of ≥50 kg N ha−1. Further, the results indicated potentials to increase wheat yield with lower GHG emissions through improved N management.