Maize is sown in Iran from mid-April to early September. Weather, weed flora and crop growth stage all vary over this time span, which changes herbicide efficacy. To avoid any excessive or inadequate usage of herbicide, we propose an empirical model that predicts the optimum dose based on the thermal time accumulated by maize after sowing. We planted maize in May and August in 2016 and 2017, arranged in a split-plot design with four replications. Main plots were herbicide timing ranging from 2 to 8 leaves of maize, and sub-plots were herbicide dose. Weed response to herbicide dose was parameterised using the standard dose–response model against thermal time (TT) of application. The parameter W₀ weed fresh weight (WFW) in plots not treated with herbicide increased linearly, ED50 (the dose to decrease W₀ by 50%) increased exponentially, and b (the slope of the curve at linear decrease) decreased exponentially with TT. We replaced the parameters by their specified function of change over TT resulting in a combined model, which predicts WFW from herbicide dose and application time. A hyperbolic model described the yield loss as a function of WFW. We included this relationship in a more developed model, which predicts per cent yield loss based on herbicide dose and application TT. The model performed well over validation tests with R² ≥ 0.90. We recommend an early herbicide application not later than 600 TT after maize sowing that allows reduced dose, as we found a steady decrease in herbicide efficiency with delaying application time.

中文翻译：

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优化玉米除草剂用量的热时间模型

玉米从 4 月中旬到 9 月初在伊朗播种。天气、杂草植物群和作物生长阶段在这段时间内都发生了变化，这会改变除草剂的功效。为避免除草剂的任何过度或不足使用，我们提出了一个经验模型，该模型根据玉米播种后积累的热时间来预测最佳剂量。我们在 2016 年和 2017 年的 5 月和 8 月种植了玉米，采用四次重复的裂区设计。主要地块是玉米 2 到 8 片叶子的除草剂时间，子地块是除草剂剂量。杂草对除草剂剂量的反应使用标准剂量-反应模型对应用的热时间 (TT) 进行参数化。参数W ₀未用除草剂处理的地块中的杂草鲜重 (WFW) 呈线性增加，ED50（使W ₀减少 50%的剂量）呈指数增加，b（线性减少时的曲线斜率）随 TT 呈指数下降。我们用它们指定的 TT 变化函数替换了参数，从而产生了一个组合模型，该模型根据除草剂剂量和施用时间预测 WFW。双曲线模型将产量损失描述为 WFW 的函数。我们将这种关系包含在一个更发达的模型中，该模型根据除草剂剂量和应用 TT 预测产量损失百分比。该模型在R ^{2 的}验证测试中表现良好≥ 0.90。我们建议在玉米播种后不迟于 600 TT 尽早施用除草剂，这样可以减少剂量，因为我们发现延迟施用时间会导致除草剂效率稳步下降。