Existing data in the United States are insufficient for estimating pesticide-treated crop areas at the watershed scale. The objective of this research was to evaluate an approach for estimating simazine usage on corn (Zea mays L.) based on its transport to streams of the Salt River Basin (SRB) of Missouri, USA. Annual loads of total simazine and atrazine (parent + metabolites) were quantified for seven SRB watersheds from 2005 to 2017. Simazine-treated corn area was computed as the total simazine load (g) divided by total atrazine load (g ha^–1) on a treated area basis; atrazine was used as surrogate in the absence of treated area simazine load data. From 2005 to 2010, an estimated 3.8–31% of the corn area within SRB watersheds was treated with simazine, and four of six watersheds had <10% of corn treated. In contrast, Long Branch Creek (2005–2017) and its sub-watersheds (2012–2017) had ≥20% of corn area treated with simazine. Key sources of variation in treated area estimates included extremely dry years with little simazine transport and disparities between spring-applied atrazine and fall-applied simazine transport. However, compared with national estimates for the SRB, these results estimated simazine usage that was generally one to two orders of magnitude greater and showed far more spatial and temporal variation among watersheds. These results demonstrated that this broadly applicable output-based method is a significant improvement over existing input-based national data for estimating pesticide usage in watersheds.

中文翻译：

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基于年河流负荷估算流域中西玛津处理面积

美国现有的数据不足以估计流域范围内经过农药处理的作物面积。本研究的目的是评估西玛津在美国密苏里州盐河盆地 (SRB) 河流中的运输，评估玉米 ( Zea mays L.) 中西玛津的用量。从 2005 年到 2017 年，对七个 SRB 流域的西玛津和莠去津（母体 + 代谢物）的年度负荷进行了量化。 西玛津处理的玉米面积计算为西玛津总负荷 (g) 除以莠去津总负荷 (g ha ^–1) 以处理面积为基础；在没有处理区域西玛津负荷数据的情况下，莠去津被用作替代品。从 2005 年到 2010 年，估计 SRB 流域内 3.8-31% 的玉米面积用西玛津处理，六个流域中有四个被处理的玉米<10%。相比之下，Long Branch Creek（2005-2017）及其子流域（2012-2017）有≥20%的玉米面积用西玛津处理。处理面积估计值变化的主要来源包括极端干旱年份，几乎没有西玛津转运以及春季施用的阿特拉津和秋季施用的西玛津转运之间存在差异。然而，与国家对 SRB 的估计相比，这些结果估计西玛津的使用量通常要高一到两个数量级，并且流域之间的空间和时间变化要大得多。