Determination of nitrogen and phosphorus fertilisation rates for tobacco based on economic response and nutrient concentrations in local stream water

Abstract

Fertilisation, although it improves crop yield and enhances farmer income, can contribute to freshwater pollution. Thus, it is important to determine the recommended fertilisation rate that can ensure crop yield and farmer income, as well as not harm the environment. We calculated the yield and net income of tobacco and measured the nitrogen (N) and phosphorous (P) concentrations under different fertilisation rates in plot runoff and local stream water during 2017 and 2018. Tobacco yield increased with increasing fertilisation rates, but net income decreased at extremely high rates. The opposite pattern was observed for the fertiliser nutrient use efficiency (NUE). When fertilisation was applied, the N and P concentrations in the runoff exceeded the established national thresholds, and the concentrations and discharges of N and P in the runoff were positively correlated with the fertilisation rate. According to the ratio of arable land to the total watershed area, reduction characteristics of N and P in the watershed stream, and the established national thresholds, the recommended N and P2O5 annual application rates in the study area are 120 kg ha−1 for both fertilisers. The recommended rates are lower than what farmers currently apply. Therefore, reducing the synthetic fertiliser application rate should be implemented to achieve sustainable development in the study region.