In recent years, the excessive application of nitrogen and phosphorus fertilizers has caused serious pollution and eutrophication, especially in paddy fields. Accordingly, a two-year (2018-2019) study was conducted at a rice paddy field under different fertilizer application rates and straw mulching in Chengdu Plain. N and P losses through the rainfall and surface runoff in the paddy field were measured under natural rainfall conditions. The results showed that nitrogen mainly existed in the form of ammonium nitrogen, and phosphorus mainly existed in the form of soluble phosphorus in the wet deposition. The wet deposition of nitrogen and phosphorus mainly occurred in June, July, and August. Surface runoff was positively correlated with rainfall, whereas surface runoff nitrogen concentration was inversely correlated with rainfall. The highest runoff losses of TN (4.75 kg·hm-2 in 2018 and 2.68 kg·hm-2 in 2019) were produced by TR3 practice and were 26.73% and 43.32% higher than that of the conventional practice. TN runoff loss was significantly decreased by reducing the rate of N fertilizer (P<0.05). Compared with that in the conventional practice TR1, TR4 reduced the N loss by 36.33% in 2018 and 26.74% in 2019, respectively. Optimized fertilizer TR2 and nitrogen reduction practice TR4 decreased P loss from surface runoff, and high intensity rainfall could reduce the content of granular phosphorus in surface runoff. The surface runoff occurring in July, August, and September contributed mostly to the total N loss, whereas the loss of total P mainly occurred before July. Consequently, the use of balanced fertilizer and decreased nitrogen fertilization amount might be effective strategies to attenuate non-point source pollution in the Chengdu Plain in the paddy fields.
Keywords: Chengdu Plain; non-point source pollution; nutrient loss; surface runoff; wet deposition.