冬小麦生育期地下水补给量表征及水位阈值试验研究

    Quantifying groundwater contributions and threshold in the growth stages for winter wheat

    • 摘要: 作物生育期地下水补给量精量表征可准确量化灌区农田地下水的利用情况,对促进地下水资源合理使用及区域农业生产可持续发展具有重要的意义。为构建冬小麦生育期地下水补给量估算模型,探究冬小麦各生育期地下水水位临界埋深和适宜阈值,该研究通过群集式蒸渗仪开展不同地下水水位和不同灌溉处理下的冬小麦生长过程试验观测,利用率定和校核后的AquaCrop模型模拟了不同灌溉制度和地下水位埋深情景下的冬小麦生长发育和土壤水分动态变化过程。结果表明:1)不同处理冬小麦土壤含水率、冠层覆盖度、生物量和产量模拟值与实测值之间统计参数可同时达到决定系数不小于0.8、相对误差和标准化均方根误差均小于16%,可见AquaCrop模型能较好模拟冬小麦生长发育过程。2)利用校核后的AquaCrop模型模拟了52种不同灌溉处理和地下水位情景下冬小麦生长过程,构建了冬小麦生育期土壤储水量—地下水补给强度和地下水位埋深—土壤储水量的非线性回归方程;将地下水补给强度计算值与田间实测值对比验证,决定系数均在0.873及以上、相对误差不大于9.22%、均方根误差不大于0.316 mm/d、标准化均方根误差不大于11.89%。3)通过联立冬小麦生育期土壤储水量—地下水补给强度和地下水位埋深—土壤储水量的非线性回归方程,得到不同灌溉处理下冬小麦各生育期地下水水位临界埋深,可知灌溉越少地下水补给需求越强烈,临界埋深越深;分析52种模拟情景下冬小麦产量与地下水水位埋深之间的关系,可知其适宜生长的最优埋深阈值为2.0~2.5 m,此时冬小麦非充分灌溉处理(返青水+灌浆水)产量和水分利用效率均达到最优,分别为8.848 t/hm2和2.18~2.43 kg/m3。研究结果可为准确评估农田地下水贡献量以及精量灌溉决策与管理提供技术支撑。

       

      Abstract: Groundwater recharge can greatly contribute to the crop growth in farmland for the sustainable development of regional production in modern agriculture. It is crucial to precisely quantify the rational utilization of groundwater sources. Among them, groundwater recharge can be broadly classified into empirical and mechanistic models in recent years. However, some limitations are still remained in practical application, due to the complexity and highly nonlinear of groundwater recharge. In this study, a series of experiments were conducted on the winter wheat under different groundwater levels and irrigation treatments using 24 clustered large-scale lysimeters. The AquaCrop model was calibrated and validated using the soil moisture content, canopy coverage, biomass, and grain yield of winter wheat as evaluation indicators. The calibrated AquaCrop model was then utilized to simulate the growth and development of winter wheat, as well as the soil water dynamics under varying irrigation treatments and groundwater depths. An estimation model was proposed for the groundwater recharge in the period of winter wheat growth. Thereby, the critical groundwater levels were determined for the different growth stages, and the threshold depth of water table suitable for winter wheat growth. Results showed that: 1) The AquaCrop model was performed best on the growth and development of winter wheat under different irrigation treatments and groundwater levels. Simultaneously, the better performance was achieved in the statistical parameters between the simulated and measured values of soil water content, canopy coverage, biomass, and grain yield during the growth period, with the determination coefficient (R2)≥0.8, the relative error (RE) and the normalized root mean square error (NRMSE) are both<16%. 2) The validated AquaCrop model was employed to simulate the growth of winter wheat under 52 scenarios of groundwater depth and irrigation treatments. Subsequently, the nonlinear regressions of soil water storage - groundwater recharge intensity and groundwater depth - soil water storage were fitted during the growth period of winter wheat. The groundwater recharge intensity was calculated to compare with the measured values for verification. The statistical parameters fell well within the acceptable error range of the model, such as R2≥0.873, RE≤9.22%, RMSE≤0.316 mm/d and NRMSE≤11.89%. 3) The critical tables of groundwater were calculated in different growth stages of winter wheat under various irrigation treatments. The critical tables of groundwater were 3.28, 3.36 and 3.54 m, respectively, for the winter wheat during the seedling, frozen and reviving-jointing stages under irrigation. Furthermore, the critical table of groundwater was 3.38 m under the sufficient irrigation treatment in the whole growth period. There was the various behavior in the different growth periods of winter wheat under the insufficient irrigation treatments. In general, the critical table of groundwater decreased with the increasing irrigation amount. The optimal threshold water table was ranged from 2.0 to 2.5 m for the winter wheat, according to the relationship between grain yields and groundwater levels under 52 simulated scenarios. Therefore, the yield and water use efficiency (WUE) of winter wheat were simultaneously reached their optimal levels under the insufficient irrigation treatment (at reviving and filling stages), which were 8.848 t/hm2 and 2.17 to 2.43 kg/m3, respectively. The findings can also provide the technical support for the accurate assessments of groundwater contribution for the precision irrigation and decision-making management.making management.

       

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