Determinants of nitrogen use efficiency and gaseous emissions assessed from farm survey: A case of wheat in Bangladesh

CONTEXT
Nitrogen (N) is an essential input for food production, but at the same time N raises serious concerns for air, water and soil pollution due to its overuse. Research shows that N use is influenced by socio-economic factors beyond the environmental circumstances while heavily depending on the agronomic practices and technologies used. Micro-level studies based on real farm observations are still scarce in this context.

OBJECTIVE
Therefore, this study estimated N use efficiency (NUE) and its climatic and socio-economic determinants, as well as N2O and NH3 emissions from organic and inorganic fertiliser-amended fields.

METHODS
Through exploring primary data collected from 155 wheat growers from north-western Bangladesh, we estimated NUE of wheat production as the ratio of the total quantity of N produced in the harvested grain and the total quantity of N applied to soil through inorganic and organic fertilisers. Then we estimate a Tobit model to determine the socio-economic and farm-level practices influencing NUE. Finally, for N2O and NH3 emissions, we applied region-specific emission factors, which are not sensitive to management practices but can give an approximation of emission and emission intensity of the production.

RESULTS AND CONCLUSIONS
The estimated mean NUE for North-West Bangladesh was 37.4%, which widely varied across different farm categories and farming practices used. Agronomic practices, including those induced by climate change, positively contributed to NUE. NUE was higher for the farmers cultivating high-yielding, drought-tolerant, and short-duration wheat varieties. NUE significantly increased when a farmer applied a combination of organic and inorganic fertilisers. Irrigation water pricing was critical in NUE since it influences farmers' water management practices. A notable quantity of N loss as N2O (5.98 kg/ha) and NH3 (45.58 kg/ha) was emitted, and the farms managed by landless and marginal farmers emitted quantities more than others. Farmers with better landholding size, education and access to extension services operated at a relatively higher level of NUE. The policy suggestions to increase NUE include strengthening extension services, particularly for promoting a balanced supply of nutrients from organic and inorganic fertilisers, promoting volumetric irrigation water pricing and encouraging long-term tenurial arrangement.

SIGNIFICANCE
The paper is relevant to policy makers since, unlike earlier works based on experimental data, it estimates more robust indices of NUE and considers the role of different farms and farmer-specific socio-economic, anthropogenic and institutional factors in farm production. Finally, the paper estimates N2O and NH3 emissions associated with wheat production.