Nitrogen and phosphorus nutrient balance and environmental risk assessment of apple orchard in Qixia city

Abstract: Qixia city is one of the most important apple producing areas in China. In recent years, a large amount of per unit area nutrient input of orchards had resulted in excessive enrichment of nitrogen and phosphorus in the region, which had further polluted the local soil, water resources, atmosphere and other environmental elements. Therefore, it was of great practical significance to clarify the current situation of fertilization in main producing areas of apple and scientifically evaluate the environmental risks. Taking Qixia city as the research area, from May to July 2018, the basic situation, fertilization pattern and fertilization quantity of apple orchards in this area were obtained through field investigation and questionnaire survey. From August to November 2018, a field experiment was conducted in a typical apple orchard to obtain nitrogen gas loss data of base fertilizer in apple orchard. From December 2018 to March 2019, nitrogen gas loss data of apple orchards were obtained by laboratory simulation. Based on quantifying the input and output of nitrogen and phosphorus nutrients in apple orchards, the surplus nitrogen and phosphorus nutrients of apple orchards in Qixia city was calculated by constructing a nutrient balance model. Finally, by dividing the environmental risk grade of nitrogen and phosphorus surplus in apple orchards, the regional environmental risk of Qixia city was evaluated comprehensively. The results showed that: 1) In 2018, nutrient input of apple orchards in Qixia city was as follows: organic matter 5 360.28 kg/hm2, N 545 kg/hm2, P2O5 568.76 kg/hm2, K2O 712.57 kg/hm2. Among them, N, P2O5 and K2O input through base fertilizer accounted for 82.23%, 81.82% and 70.41% of the total. Only 17.77%, 18.18% and 29.59% were absorbed through top dressing; 2) Gaseous loss of nitrogen, fruit and branch carry away accounted for 6.49%, 24.34% and 3.12% of the total input, respectively, with a surplus rate of 66.04% (402.97 kg/hm2). The phosphorus taken away by fruits and branches accounted for 12.33% and 2.55% of the total input, respectively, with a surplus rate of 85.12% (484.75 kg/hm2). The surplus amounts of nitrogen and phosphorus in Qixia city both exceed the threshold of environmental safety, which belong to the range of medium risk and high risk respectively. In conclusion, excessive application of nitrogen and phosphorus fertilizers will inevitably pose a threat to the soil, land surface and groundwater resources and atmospheric environment of Qixia city. Therefore, on the premise of ensuring the output and quality of orchards, it should be the main direction of sustainable development of orchards to appropriately reduce the use of chemical fertilizer, gradually establish an integrated fertilization model of water and fertilizer, and improve the management experience of fruit farmers.