冬灌对冻融期干旱区荒漠绿洲农田土壤水热状况的影响

冬灌可显著改善土壤水热状况,对缓解"春旱"和促进农作物生长发育具有积极的影响。文章通过探究冻融期干旱荒漠区不同开垦年限的农田土壤水热变化特征,揭示冬灌对土壤水热变化及农田水量平衡的影响,为荒漠绿洲农田水分管理提供理论借鉴。研究选取了黑河中游荒漠绿洲过渡带新垦绿洲农田土壤和老绿洲农田土壤(灌耕风沙土和灌耕灰棕漠土),利用土壤温湿度监测仪(ECH_2O)测定的土壤含水量和土壤温度及模拟土柱测定的渗漏损失量,分析了冻融期土壤水热动态变化过程及冬灌对深层渗漏损失的影响。结果表明:老绿洲农田消融历时(26 d)显著长于新垦绿洲农田(12 d),新垦绿洲农田消融历时短不利于春季土壤水分的保持;且翌年土壤完全融化后,新垦绿洲农田浅层(0～40 cm)贮水量低于老绿洲农田;此外,160 mm的冬灌事件导致新垦绿洲农田深层渗漏量为老绿洲农田的4.1倍。新垦绿洲农田需考虑补充灌溉以保证春播作物正常出苗,老绿洲农田"蓄水保墒"生态效应优于新垦绿洲农田。因此,在干旱区荒漠绿洲过渡带农田水分管理中,需综合考虑深层渗漏和"冻后聚墒"效应,针对土壤质地差异实施动态的冬灌策略以保证灌溉水资源优化利用。

Effects of winter irrigation on soil hydro-thermal features in desert oasis farmland in arid area during freezing and thawing period

Abstract: Winter irrigation has proven to have positive effects on alleviating the "spring drought" and promoting the growth of crops. In seasonally frozen regions, a special rule of soil hydro-thermal movement is formed during the process of freezing and thawing. However, few studies have focused on the effects of winter irrigation on soil hydro-thermal dynamics in the farmland ecosystem of arid desert areas. Therefore, the aim of this study was to investigate the soil hydro-thermal features during the freezing-thawing period after winter irrigation with simulated soil column experiment. The experiment was conducted in marginal farmlands of oasis in middle Hexi Corridor region, Gansu, China. It was located in arid and semi-arid desert-oasis areas. Two types of soil, i.e. ploughed aeolian sandy soil (newly cultivated sandy cropland) and ploughed grey-brown desert soil (old oasis cropland), were backfilled into the soil columns. Each type of soil had 3 repetitions. Winter irrigation (160 mm) was conducted on October 31, 2016. Then the ECH2O soil moisture-temperature sensors were employed to measure soil moisture content and soil temperature at 10, 20, 40, 60, 80, 100, 120, 140, 160 and 180 cm soil depth from November 11, 2016 to April 11, 2017. In addition, the processes of soil water leakage were simulated and the effect of winter irrigation on deep leakage was analyzed. The results showed that an obvious difference existed in soil hydro-thermal dynamics between newly cultivated sandy cropland and old oasis cropland during the freezing-thawing period. In superficial layer (from 0 to 40 cm) and middle layer (from 40 to 100 cm), soil moisture content of the 2 types of soil reached the lowest level in January, and was basically recovered to the pre-freezing level after the soil thawed completely in April, and the soil water storages in these 2 layers in old oasis cropland were higher than that in newly cultivated sandy cropland. However, the change of soil water storage in deep layer (from 100 to 200 cm) was small for the 2 types of soil during the observation period. On January 18, 2017, the soil freezing depth of newly cultivated sandy cropland and old oasis cropland reached the highest value, and the highest value was 105 and 74 cm, respectively. Meanwhile, the duration of soil thawing process of old oasis cropland (26 d) was longer than that of newly cultivated sandy cropland (12 d). Nevertheless, the less thawing time for newly cultivated sandy cropland was detrimental to the soil water retention in spring. In addition, a significant difference in the deep leakage also existed between the 2 types of soil caused by winter irrigation. The deep leakage amount of newly cultivated sandy cropland was 4.1 times that of old oasis cropland when the winter irrigation amount was 160 mm. Above results suggested that the supplementary irrigation was necessary to ensure the germination of crops in spring in newly cultivated sandy cropland. Moreover, the "water preservation" effect in old oasis cropland was better than newly cultivated sandy cropland. As for different soil types, "water preservation" effect and lower deep leakage loss should be considered to ensure the optimal utilization of irrigation water resources in the desert oasis farmland management.