1.College of Natural Resources and Environment, Northwest A&2.F University;3.CInstitute of Soil and Water Conservation, Northwest A&4.F University / The State Key Laboratory of Soil Erosion and Dryland Farming on Loess Plateau,;5.amp;6.F University/Institute of Soil and Water Conservation, Northwest A&7.F University / The State Key Laboratory of Soil Erosion and Dryland Farming on Loess Plateau
the National Natural Science Foundation of China (41877072) and the Natural Science Foundation of Shaanxi Province (2019JQ-639).
近年来，草甘膦及其降解产物氨甲基磷酸 (AMPA)在土壤中的持久性及其环境风险日益受到关注。然而，草甘膦与磷酸盐结构相似且带电荷，可能与磷酸盐在土壤颗粒表面产生吸附竞争，进而影响其在土壤中的环境行为及土壤 磷的生物有效性。本研究通过室内控制试验，对不同磷肥施用水平(0，50 mg.kg-1，100 mg.kg-1)及水分条件下 (20%田间持水量 (20FC)，60%田间持水量 (60FC))，黄土中草甘膦农药降解动力学、土壤速效磷及土壤酶活性变化特征进行研究。结果表明：1) 不同磷肥施用及水分条件下，草甘膦农药在喷施初期降解速率较快，后期逐渐减缓；不同磷肥施用水平对草甘膦降解影响不显著，但不同水分梯度对其影响差异显著。其降解产物AMPA的含量随着草甘膦农药的降解而增加，不同磷肥施用水平处理AMPA的含量差异不显著，但不同水分条件下其峰值及变化特征差异显著，即：20FC 条件下到喷施后第14 d达到峰值，而60FC条件下在喷施后第7d 就达到峰值。通过拟合发现，草甘膦残留数量特征符合污染物一级动力学衰减模型，其半衰期分别为 69.3~77.0 d (20FC)和10.5~12.8 d (60FC)。2) 草甘膦农药喷施后，土壤中速效磷含量随草甘膦农药的降解呈现先减小后增大的变化特征，土壤水分对其影响差异显著。此外，草甘膦农药喷施后，磷酸酶活性受到明显抑制，N-乙酰胺基-β-葡萄糖苷酶、β-葡萄糖苷酶、亮氨酸酶活性波动较大。不同磷肥施用水平对以上四种土壤酶活性的影响差异不显著，但不同水分梯度对其影响较大。由此表明：黄土中磷水平对草甘膦农药降解特征的影响不显著，但土壤水分状况显著影响草甘膦农药的衰减速率及其降解产物的残留水平；同时，草甘膦农药喷施，对黄土中速效磷及磷酸酶活性的影响较大，可能对土壤P循环及植物利用产生影响。因此，后续研究还应考虑草甘膦与土壤磷组分及相关酶活性的互馈效应，特别是在干旱条件下草甘膦及其降解产物的持久性与土壤健康的关系研究，以期为黄土区草甘膦农药的安全喷施提供科学依据。
In recent years, more attention has been paid to the persistence of glyphosate and its degradation product, ammethylphosphoric acid (AMPA), in soil, as well as their environmental risks. However, with a similar structure as phosphate and with a positive charge, glyphosate may compete with phosphate for adsorption sites on the surface of soil particles, thereby affecting its environmental behavior and the bioavailability of phosphorus in soil.【Objective】Our aim was to investigate the degradation kinetics of glyphosate pesticide, soil available phosphorus and soil enzyme activity in Loess soil.【Method】Laboratory experiments were carried out under different phosphate application levels (0, 50, and 100 mg.kg-1) and water conditions (20% field water capacity (20FC) and 60% field water capacity (60FC)).【Result】The results showed that: 1) The degradation rate of glyphosate was fast at the initial stage of spraying and gradually slowed down at the later stage under different levels of phosphate application and soil moisture. Different phosphate levels had no significant effect on glyphosate degradation while different soil moisture did. Also, the content of AMPA increased with the degradation of glyphosate, and there was no significant difference in the content of AMPA under different phosphate levels. However, the peak and variation characteristics of AMPA under different soil moisture significantly differed. The peak was reached on day 14 after spraying for 20FC and on day 7 for 60FC. In addition, the quantitative characteristics of glyphosate residues fitted the first-order kinetic degradation model, with a half-life time of 69.3~77.0 d (20FC) and 10.5~12.8 d (60FC). 2) After spraying glyphosate, the content of available phosphorus decreased first and then increased with the degradation of glyphosate, which was significantly affected by soil moisture. In addition, phosphatase activity was significantly inhibited after glyphosate application, while the activities of N-acetylamino-β-glucosidase, β-glucosidase and leucine aminopeptidase changed dynamically. Phosphate levels showed no significant effects on soil enzymes’ activities while soil moisture did.【Conclusion】The findings indicate that phosphorus level in Loess soil had no significant effect on the degradation characteristics of glyphosate, but soil moisture significantly affected the degradation rate of glyphosate and the residual level of its metabolite. Meanwhile, glyphosate application had a significant effect on the activities of available phosphorus and phosphatase, which may affect soil phosphorus cycling and plant utilization. Therefore, the feed-effects of glyphosate and soil phosphorus components as well as the related enzyme activities should be considered in follow-up studies, especially the relationship between the persistence of glyphosate and its metabolite and soil health indicators under drought conditions. This will provide scientific-based information to guide glyphosate use in Loess soil regions.
DingLingling, XueSha, Yang Xiaomei. Effect of Soil Moisture and Phosphorus Level on Degradation Kinetics of Glyphosate Pesticides[J]. Acta Pedologica Sinica,,[In Press]