Croplands conversion to cash crops in dry regions: Consequences of nitrogen losses and decreasing nitrogen use efficiency for the food chain system

Understanding the effects of land-use change in drylands on nutrient use efficiencies and losses within the food production-consumption system provides insights on nutrient management strategies and the effectiveness of land-use policies. Weibei Dryland is considered an example to use to evaluate changes in nitrogen (N) flows through the food chain following conversion of croplands to apple orchards, using the Nutrient flows in Food Chains, Environment and Resources Use (NUFER) model, and we also modelled the effects of 20% reduction in N fertilizers on apple yields to obtain a balanced fertilization strategy. The apple orchards area increased from 9.6 × 10⁴ ha in 1978 to 72 × 10⁴ ha in 2013, while the area under cereals decreased from 186 × 10⁴ ha in 1978 to 152 × 10⁴ ha in 2013. The increased income due to apple orchards led on-one-hand to more N fertilization to get a higher apple yield, and on-the-other-hand promoted the consumption of animal foods. Consequently, nitrogen use efficiency of crop production (NUEc) and the combination of crop and animal production (NUEc+a) decreased, but nitrogen use efficiency of animal production (NUEa) and N losses increased between 1978 and 2013. The modelled scenario of 20% reduction in N fertilization amounts will still keep optimum apple yield but will significantly decrease N losses from the apple orchards. We therefore, suggest that the key measures for improving nitrogen use efficiency and decreasing N losses after conversion to cash crops are: (a) reducing N fertilization as well as balancing various inorganic fertilizers; and (b) implying organic fertilizers.