Abstract:

【Objective】The objective of this study is to reveal the flow characteristics of nitrogen (N) and phosphorus (P) in manure and their effects to the environment during the development of livestock and poultry breeding in Hainan, and to provide references for regional agricultural development planning and adjustment of livestock and poultry breeding structure. 【Method】Based on the statistical data and literature data, the nutrient yield of animal manure and nutrient carrying capacity per unit cultivated area in Hainan Island from 1988 to 2018 were estimated, and their effects to the environment were deeply analyzed by using alarm value and environmental risk index. When the alarm value is less than 0.4, it can be considered as no threat to the environment, and when the environmental risk index is below 1.00, the risk to the environment can be ignored, above these safety values will have different degrees of impacts on the environment. 【Result】From 1988 to 2018, the changes of the animal manure amount in Hainan Island experienced three stages. The total amount of animal manure increased from 1988 to 2005, and decreased a lot from 2006 to 2008. Since then it developed slowly and stabilized, and the amount of animal manure produced in 2018 was 10.50×10⁶t. In terms of nutrient yield, the annual variation trends of nitrogen and phosphorus were similar, with the largest yield in 2005 and a relatively large decline in 2006. To 2018, the yields of nitrogen and phosphorus in manure were 7.41×10⁴ and 1.01×10⁴ t, respectively. The nitrogen and phosphorus loads per unit cultivated land area also experienced a stable trend after continuous increasing. To 2018, cultivated land nitrogen load was 168.80 kg·hm^-2, and cultivated land phosphorus load was 23.05 kg·hm^-2. In 2018, regional variations were relatively large. The nitrogen and phosphorus loads per unit cultivated area were higher in eastern and northern regions, while lower in western and central regions. The highest nitrogen and phosphorus loads were Dingan (288.50 and 40.35 kg·hm^-2, respectively), and the lowest were Dongfang (61.66 and 8.83 kg·hm^-2, respectively). In terms of environmental effects, the alarm values of animal manure per cultivated land from 1988 to 2018 were always at high levels, most years between 1.0 to 1.5, which belonged to the classification standard of IV level and had a serious threat to the environment. In 2018, the alarm values in Dingan and Chengmai were 2.66 and 4.59 (reached the VI level), which had a serious threat to the environment, while only Dongfang was at a safe level with the alarm value of 0.36, which reached the I level. According to the environmental risk assessment results, the environmental risk of animal manure in cultivated land in Hainan Island was relatively high. In recent years, with the total amount of animal breeding reduction, the environmental risk indexes in 2018 dropped to 1.99 (N) and 1.32 (P), respectively. At the regional level, for nitrogen pollution, the environmental risk index of Dingan was the highest (3.39), while the lowest (0.73) was Dongfang; for phosphorus pollution, the environmental risk index in Dongfang (0.50) was the lowest in 2018, which can be considered that phosphorus in Dongfang had a low potential threat to the environment, while Dingan had a serious impact on the environment, with a value as high as 2.31. In general, both the alarm value and the environmental risk index indicated that the potential environmental risk of animal manure pollution in Hainan Island was serious, from the perspective of spatial distribution, environmental risks in eastern cities and counties such as Dingan and Wanning were higher than those in western regions such as Lingao and Dongfang, and most cities and counties posed a higher degree of threat to the environment. 【Conclusion】Due to the influence of animal breeding scale and cultivated land area, the nitrogen load per cultivated land area in Hainan Island is relatively high, and the potential environmental risks of the region scales cannot be ignored. Therefore, the future development plan of livestock and poultry breeding in Hainan Island should focus on the control of pollutants, regional distribution and management, meanwhile, realize the utilization of animal manure resources and the green development of Hainan Island by reducing the animal manure discharge to the environment and adopting resource recycling modes.

Key words: Hainan Island, animal manure, loads of nitrogen and phosphorus, environmental effect