Malone Robert W, Weatherington-Rice Julie, Shipitalo Martin J, Fausey Norman, Ma Liwang, Ahuja Lajpat R, Wauchope R Don, Ma Qingli
USDA-Agricultural Research Service, National Soil Tilth Laboratory, 2150 Pammel Dr, Ames, IA 50011, USA.
Pest Manag Sci. 2004 Mar;60(3):277-85. doi: 10.1002/ps.791.
Within-event variability in rainfall intensity may affect pesticide leaching rates in soil, but most laboratory studies of pesticide leaching use a rainfall simulator operating at constant rainfall intensity, or cover the soil with ponded water. This is especially true in experiments where macropores are present--macroporous soils present experimental complexities enough without the added complexity of variable rainfall intensity. One way to get around this difficulty is to use a suitable pesticide transport model, calibrate it to describe accurately a fixed-intensity experiment, and then explore the affects of within-event rainfall intensity variation on pesticide leaching through macropores. We used the Root Zone Water Quality Model (RZWQM) to investigate the effect of variable rainfall intensity on alachlor and atrazine transport through macropores. Data were used from an experiment in which atrazine and alachlor were surface-applied to 30 x 30 x 30 cm undisturbed blocks of two macroporous silt loam soils from glacial till regions. One hour later the blocks were subjected to 30-mm simulated rain with constant intensity for 0.5 h. Percolate was collected and analyzed from 64 square cells at the base of the blocks. RZWQM was calibrated to describe accurately the atrazine and alachlor leaching data, and then a median Mid-west variable-intensity storm, in which the initial intensity was high, was simulated. The variable-intensity storm more than quadrupled alachlor losses and almost doubled atrazine losses in one soil over the constant-intensity storm of the same total depth. Also rainfall intensity may affect percolate-producing macroporosity and consequently pesticide transport through macropores. For example, under variable rainfall intensity RZWQM predicted the alachlor concentration to be 2.7 microg ml(-1) with an effective macroporosity of 2.2 E(-4) cm(3) cm(-3) and 1.4 microg ml(-1) with an effective macroporosity of 4.6 E(-4) cm(3) cm(-3). Percolate-producing macroporosity and herbicide leaching under different rainfall intensity patterns, however, are not well understood. Clearly, further investigation of rainfall intensity variation on pesticide leaching through macropores is needed.
降雨强度的事件内变异性可能会影响土壤中农药的淋溶速率，但大多数农药淋溶的实验室研究使用的是在恒定降雨强度下运行的降雨模拟器，或者是用积水覆盖土壤。在存在大孔隙的实验中尤其如此——大孔隙土壤本身就存在实验复杂性，再加上降雨强度变化带来的额外复杂性。解决这一难题的一种方法是使用合适的农药运移模型，对其进行校准以准确描述固定强度实验，然后探讨降雨强度在事件内的变化对农药通过大孔隙淋溶的影响。我们使用根区水质模型（RZWQM）来研究降雨强度变化对甲草胺和莠去津通过大孔隙运移的影响。数据来自一项实验，在该实验中，将莠去津和甲草胺地表施用于来自冰川冰碛地区的两种大孔隙粉质壤土的30×30×30厘米原状土块上。一小时后，土块接受强度恒定的30毫米模拟降雨，持续0.5小时。从土块底部的64个方形单元格中收集并分析渗滤液。对RZWQM进行校准以准确描述莠去津和甲草胺的淋溶数据，然后模拟一场中西部中等强度的可变强度暴雨，其初始强度较高。与相同总深度的恒定强度暴雨相比，可变强度暴雨使一种土壤中甲草胺的损失增加了四倍多，莠去津的损失几乎增加了一倍。此外，降雨强度可能会影响产生渗滤液的大孔隙度，从而影响农药通过大孔隙的运移。例如，在可变降雨强度下，RZWQM预测甲草胺浓度为2.7微克/毫升，有效大孔隙度为2.2×10⁻⁴立方厘米/立方厘米；浓度为1.4微克/毫升时，有效大孔隙度为4.6×10⁻⁴立方厘米/立方厘米。然而，不同降雨强度模式下产生渗滤液的大孔隙度和除草剂淋溶情况尚未得到很好的理解。显然，需要进一步研究降雨强度变化对农药通过大孔隙淋溶的影响。
