广东稻田氮素径流流失特征

2008—2012年间,对分布于粤中、粤北和粤西的增城、清远和高州三个稻田试验点进行了连续5年的径流养分定点监测试验,研究当地农户常规施肥模式下稻田氮素养分的径流流失特征及其潜在环境风险。径流监测结果表明,三个试验点的稻田径流事件主要发生在早稻季节。增城、清远和高州试验点施肥处理铵态氮浓度分别为0.05~25.05、0.02~19.83 mg·L-1和0.02~55.4 mg·L-1,总氮浓度分别为0.33~36.51、0.46~21.01 mg·L-1和0.49~61.96 mg·L-1。结果显示,施肥明显增加径流水铵态氮和总氮含量,施氮后10 d内径流水铵态氮和总氮浓度均高于地表水Ⅴ类水标准(2.0 mg·L-1),具有一定的环境污染风险;施氮对径流水硝态氮浓度具有一定影响,三个试验点径流水硝态氮浓度均在10 mg·L-1的地表水标准限值内;稻田氮年流失负荷表现出时空差异性大的特点,增城、清远和高州试验点施肥处理总氮年流失负荷分别为24.31~53.68 kg·hm-2、8.71~23.76 kg·hm-2和13.32~88.16 kg·hm-2,相应氮流失系数为1.4%~3.9%、0.1%~5.5%和0.9%~21.6%。不同稻季总氮流失分析显示,53%~86%的总氮流失负荷发生在早稻季,与本地区降雨时间分布有直接关系。

Characteristics of Nitrogen Runoff from Paddy Fields in Guangdong Province

Nitrogen loss from agricultural fields is a important source for eutrophication in aquatic ecosystems. In this study, characteristics and potential environmental risks of nitrogen runoff were studied from 2008 to 2012 under conventionally managed paddy fields in Zengcheng, Qingyuan and Gaozhou, which represent central, north and western regions of traditional paddy production area in Guangdong Province, respectively. Nitrogen runoff from paddy fields occurred mainly during the early period of rice growth in these regions, which was associated with the local precipitation. In nitrogen fertilization treatment, concentrations of NH₄⁺-N in runoff water were from 0.05 to 25.05 mg·L^-1, 0.02 to 19.83 mg·L^-1, and 0.02 to 55.4 mg·L^-1 for Zengcheng, Qingyuan and Gaozhou region, respectively. The corresponding total nitrogen(TN) concentrations were from 0.33 to 36.51 mg·L^-1, 0.46 to 21.01 mg·L^-1, and 0.49 to 61.96 mg·L^-1. Nitrogen application increased the concentrations of NH₄⁺-N and TN in runoff water from paddy fields, both exceeding the grade V(2.0 mg·L^-1) of the national surface water quality standards within 10 days after nitrogen application, implying that nitrogen runoff during this period would impose potential risks to the water environment. Although nitrogen fertilization affected NO₃^--N concentrations in the runoff water, it was less than 10 mg·L^-1 in all three experimental regions. The nitrate concentrations in the runoff met the fifth grade(grade V) of national surface water quality standards. Annual loads of nitrogen runoff in Zengcheng, Qingyuan and Gaozhou regions were from 24.31 to 53.68 kg·hm^-2, 8.71 to 23.76 kg·hm^-2 and 13.32 to 88.16 kg·hm^-2, respectively, and the corresponding runoff coefficients were from 1.4% to 3.9%, 0.1% to 5.5% and 0.9% to 21.6%. Approximately 53% to 86% of nitrogen runoff loads were observed in the early rice season, which was directly related to the local rainfall distribution.