黄土塬区旱作冬小麦土壤水分利用特征的稳定同位素分析

Stable Isotope Analysis of Soil Water Utilization by Winter Wheat in Dryland of Loess Tableland

通过对长武黄土塬区遮雨样地和自然样地3 m深度土壤水标记氘水(D2O),并测定旱作冬小麦不同生育期茎秆水、降水、不同土层土壤水δD和δ18 O值,利用稳定同位素技术明确旱作冬小麦能否利用3 m深度土壤水分,并定量分析其对不同土层土壤水分利用比例及对降雨量减少的响应。结果表明:(1)旱作冬小麦自开花—灌浆期开始利用3 m深度土壤水分,其对各层土壤水分的利用强度具有随深度增加而减小的趋势;(2)抽穗期至乳熟期,0—50 cm土壤水对冬小麦耗水的贡献率为28.0%~36.7%,50—100 cm土壤水为24.7%~32.3%,100—200 cm土壤水为15.7%~22.3%,200—300 cm土壤水为11.4%~17.4%;300—400 cm土壤水对灌浆期—乳熟期冬小麦耗水贡献率为15.6%~16.6%;(3)降雨量减少没有改变旱作冬小麦对3 m深度土壤水分利用的起始时间,但是提升了其对深层土壤水分的利用强度,以满足生育耗水的需求。黄土塬区深层土壤储水对于保障冬小麦水分供给具有重要意义,生产实践中需要做好夏闲期蓄水保墒措施,促使深层土壤水分恢复,保证土壤水库调蓄功能的持续发挥。

In this paper, soil water at the depth of 300 cm both in the rain cover plot and the natural plot in Changwu Loess Tableland were marked by deuterium water, and the δD and δ18 O values of wheat stem water, rainwater and soil water samples in different layers in different growth stages of winter wheat were measured to determine whether winter wheat can use the soil water in 300 cm depth. Further, the utilization of soil water in different soil layers by winter wheat in dryland and its response to the reduction of precipitation were analyzed. The results show that:(1) winter wheat begins to use soil water in 300 cm depth since the flowering-filling stages, and the utilization of soil water in different soil layers decrease with the increase of soil depth;(2) from the heading stage to the milk, the contribution rates of soil water in 0—50 cm, 50—100 cm, 100—200 cm and 200—300 cm layer to the water consumption of winter wheat were 28.0%~36.7%, 24.7%~32.3%, 15.7%~22.3% and 11.4%~17.4%, respectively, and the contribution rate of soil water in 300—400 cm depth was 15.6%~16.6% during the filling and milk ripening stages;(3) reduction of precipitation dose not change the time of winter wheat use soil water in 300 cm depth, but increases the utilization rate of soil water from deep soil layer, so as to meet the water demand during the growing period. Overall, soil water storage in deep layer is significant for winter wheat in dryland of the loess tableland. Therefore, it is necessary to take effective measures to improve the soil water storage during the fallow period in summer in production practice, so as to promote the recovery of soil water in deep layer and maintain sustainable regulation and storage function of the soil reservoir.