有机无机肥配施模式对氮素淋失的影响

为了探索农田氮素淋失低风险的有机无机肥配施模式，该研究收集了331个有效农田有机肥化肥配施数据对，分析了施肥总量、施肥结构（有机肥替代比）、施肥时间（基追施）、有机肥种类等因素对氮素淋失的总体影响。结果表明：与单施化肥相比，有机肥配施化肥中氮素总量较低时（N<200 kg/hm2），农田总氮（Total Nitrogen，TN）、硝态氮（NO3--N）淋失分别减少36.77%、65.05%；有机肥替代比高于70%，虽然可减少TN淋失（39.64%），但增加了溶解性有机氮（DON）淋失的风险（15.78%），尤其是动物型有机肥替代化肥使DON淋失增加26.31%；氮肥基施可显著降低TN、NO3--N淋失（43.58%、70.51%，P<0.05）。碱性旱地土壤上有机肥配施化肥可有效抑制TN、NO3--N淋失，但增加了26.63%～42.95%的DON淋失。旱地氮素淋失以NO3--N为主，且淋失系数高于水田，提高有机肥替代比可以大幅降低旱地氮素淋失，但增强了DON淋失。因子重要性分析表明：有机肥替代比对TN淋失影响占主导作用，而施氮水平对NO3--N、DON淋失影响更为重要。因此，低施氮量、高替代比动物型有机肥可有效减少碱性旱地土壤氮素淋失，为有机肥配施化肥的农田应用提供依据。

Meta-analysis of the effects of combined application of organic and chemical fertilizers on soil nitrogen leaching

Abstract: Nitrogen is one of the most essential elements for crop growth. Nitrogen fertilizer has been widely applied to increase crop yields. At the same time, a large number of negative impacts have posed a great threat to the ecological environment in recent years. Among them, nitrogen leaching can be attributed to the excessive application of chemical fertilizers in farmland. Fortunately, the combined application of organic and chemical fertilizers can be expected to effectively reduce soil nitrogen leaching in normal fertilization during agricultural production at present. Therefore, this study aims to explore the combination application mode of organic and chemical fertilizers with a low risk of nitrogen leaching in farmland. The search terms were selected as chemical fertilizer, organic fertilizer, and nitrogen leaching using the two databases of China National Knowledge Infrastructure (CNKI) and Web of Science. The peer-reviewed and published papers were then obtained up to January 2022. Finally, a total of 35 papers (22 papers from Web of Science, 13 papers from CNKI) and 331 effective data pairs were collected after screening for the combination application of organic and chemical fertilizers in farmland. The target variables were taken as the total nitrogen (TN), nitrate nitrogen (NO3--N), and dissolved organic nitrogen (DON), while the chemical fertilizer was the control. After that, Metawin 2.1 software was used to determine the overall effects of the total amount of fertilization, fertilization structure (organic fertilizer substitution ratio), fertilization time (basic topdressing), and the types of organic fertilizers on the nitrogen leaching, where the chemical fertilizer was as the control. The results showed that there was a significant influence of the above fertilization behavior on nitrogen leaching. Once the total amount of nitrogen was less than 200kg/hm2, the leaching of TN and NO3--N in farmland decreased by 36.77% and 65.05%, respectively. When the substitution ratio of organic fertilizers was higher than 70%, the TN leaching was reduced by 39.64%, whereas the risk of dissolved DON leaching increased by 15.78%. Especially, there was a 26.31% increase in DON leaching in the application of animal-based organic fertilizers combined with chemical fertilizers. Correspondingly, the application of nitrogen fertilizer significantly reduced the leaching of TN and NO3--N by 43.58% and 70.51%(P<0.05), respectively. A certain impact was also found in the soil pH and land use patterns on nitrogen leaching. For example, the combined application of organic and chemical fertilizers on the alkaline dryland soil effectively inhibited the leaching of TN and NO3--N, whereas, there was an increase in the leaching of DON by 26.63%-42.95%. Nitrogen leaching in dryland was dominated by the NO3--N leaching. By contrast, the emission factor (EF) was higher than that in the paddy field. The increasing replacement ratio of organic fertilizers can be expected to greatly reduce the soil nitrogen leaching in dryland, but to enhance the DON leaching. In addition, the Matlab software was used to analyze the importance of factors using the random forest model. Specifically, the replacement ratio of organic fertilizer demonstrated a dominant effect on TN leaching. There was also the more important effect of the nitrogen application level on the NO3--N and DON leaching. Therefore, the low level of nitrogen application and the high substitution ratio of animal-based organic fertilizers can be used to effectively reduce the soil nitrogen leaching loss in the alkaline dryland, compared with the chemical fertilizers only. The finding can provide the practical basis for the combined application of organic and chemical fertilizers in farmland.