滴灌夏玉米土壤水分与蒸散量SIMDualKc模型估算

为研究西北半干旱地区作物蒸腾和土壤蒸发规律,以及土壤蒸发量占蒸散量的比例(简称蒸发占比),开展2 a夏玉米滴灌控水试验,设置正常灌水(W1)、适度水分亏缺(W2)和中度水分亏缺(W3)3个灌水水平.采用W2实测土壤水分数据对SIMDualKc模型进行参数率定,并采用W1和W3实测土壤水分数据对模型进行验证;进一步基于SIMDualKc模型对不同水分供应的土壤水分胁迫系数、土壤蒸发量、植株蒸腾和蒸散量进行定量模拟分析.结果表明,SIMDualKc模型可以较好地模拟西北半干旱区滴灌夏玉米不同水分供应条件下的土壤水分动态变化过程,实测值与模型预测值有较好的一致性(R2＞0.88,RMSE＜5％);夏玉米生长期,模型能较好地估算不同水分供应的土壤水分胁迫系数、土壤蒸发量和植株蒸腾.土壤蒸发主要集中在生育前期,而生育中期较低,后期略微升高.植物蒸腾主要集中在快速生长期和生长中期,整个生育期呈先增大后减小的趋势.蒸散量随着土壤蒸发和植物蒸腾的变化而变化,前期主要受土壤蒸发的影响,快速生长期、生长中期和后期主要受植物蒸腾的影响.Wl～W3处理土壤蒸发量为78.1～100.2 mm,植株蒸腾为221.8～293.3 mm,蒸散量为299.3～383.0 mm,蒸发占比为24.1％～28.7％.研究可为西北半干旱地区制定合理的夏玉米滴灌制度和灌溉决策提供理论依据.

Estimation of drip irrigated summer maize soil water content and evapotranspiration based on SIMDualKc model

Abstract: Accurate estimation of soil evaporation, crop transpiration, evapotranspiration (ET), and the ratio of soil evaporation to evapotranspiration are critical for the precise water management in areas with scarce water resources. This study aimed to evaluate the SIMDualKc model for ET estimation and partition in terms of accuracy in summer maize under drip irrigation. A 2-year controlled drip irrigation experiment was conducted in the summer maize field in semi-arid regions of northwest China. This drip irrigation experiment included 3 water-supply levels (i.e., normal irrigation, W1; moderate deficit, W2; and medium deficit, W3). The measured soil water content for W2 treatment was selected for parameter calibration in SIMDualKc model, while the measured soil water content for W1 and W3 treatments were used for model validation. Based on those, the parameters such as transpiration, soil evaporation, ET and soil water stress coefficient for each treatment were simulated and analyzed. The results showed a good agreement in the measured soil water content and the simulated values from SIMDualKc model, with R2> 0.88 and normalized root mean square error smaller than 5%, which indicated that the SIMDualKc model was suitable for describing the dynamic changes of soil water content in this experiment. The values of basal crop coefficient for summer maize at the initial-, mid-, and late-season growth stages was 0.15, 1.13, and 0.2, respectively. Furthermore, the SIMDualKc model exhibited a high accuracy in estimating soil water stress coefficient, transpiration and soil evaporation during the whole growth stage of summer maize for all the treatments, but it overestimated soil water stress coefficient before the seed emergence. Soil evaporation mainly occurred in the early growth stage. While for transpiration, it was mainly in the rapid growth period and middle growth period. It increased and then decreased in the whole growth, peaking at the development and mid-season stages. Evapotranspiration varied with changes in the soil evaporation and crop transpiration, which was mainly affected by soil evaporation at the initial stage, and by crop transpiration at the development, mid-season and later stages. Specifically, values of soil evaporation, transpiration, ET, and the ratio of soil evaporation to ET for W1-W3 were 78.1-100.2 mm, 221.8-293.3 mm, 299.3-383.0 mm, and 24.1%-28.7%, respectively. Besides, values of soil evaporation, transpiration and ET had a downward trend with the decrease in water supply amount. Compared with the W1, the W2 and W3 declined on average by 3.74%-21.7%, while the ratio of soil evaporation to ET increased with the decrease in water supply amount. The W2 and W3 treatments increased by 11.1% and 3.8% as compared to W1 during the 2 growing seasons. This study can provide a basis for the establishment of reasonable drip irrigation scheduling and irrigation decision-making for summer maize in the semi-arid regions of northwest China.