毛乌素沙地农田土壤水分动态特征研究

Research on soil water dynamics of farmland in Mu Us Sand Land

毛乌素沙地农业种植以春玉米为主,水资源短缺是制约当地农业发展的主要因素,研究农田土壤水分动态对指导当地农业生产具有重要意义。本研究以原位试验为主,通过对地下水、土壤含水率、土水势、灌溉降雨、蒸腾蒸发等数据的监测和分析,对毛乌素沙地春玉米生长过程中的土壤水分动态特征进行研究。结果表明：地下水与土壤水之间存在明显的水力联系,Pearson相关性分析发现,各深度土壤含水率与地下水埋深之间均呈显著相关,其中40-60 cm深处相关性最大,相关系数大于0.8;地下水位的下降降低了土壤含水率稳定层的位置,削弱了上下层土壤之间的水力联系,不利于土壤水分的保持;玉米需水量增加和地下水位下降均会导致土壤含水率在垂向剖面上的不规律变化增强。通过对土壤含水率和土水势监测数据的分析发现,在玉米从苗期至蜡熟期的生长过程中,土壤水分动态经历了弱—强—弱的变化过程,并且20 cm深土层是春玉米的主要吸水层,30-40 cm是相对干燥层,由于田间灌溉在春玉米发生水分胁迫时进行,因此可利用30 cm和40 cm深土层含水率判断玉米是否需要灌溉。受春玉米生理作用影响,当10 cm深处土水势值下降到低于-0.18 bar时会出现根系提水现象。本研究结果可以为毛乌素沙地地区的农田水分利用及水资源管理提供重要的理论依据和参考信息。

Soil water is a key parameter in the interactions among the earth, atmosphere and hydrological cycle. Understanding soil water dynamics is critical in studying biophysical processes of the land surface. The Mu Us Sandy Land（MUSL） in northwest China is a dominant semi-arid climate region with scarce precipitation and surface water resources and groundwater as the main sources of water. Thus as water is the main factor restricting the development of the agriculture in MUSL region, it is vital to study soil water dynamics in farmlands to guide local agricultural production. Previous studies on soil water dynamics in MUSL and shrub areas of the region failed to take into account soil water dynamics during spring maize growing season, which is the main cultivation period in MUSL region. Therefore in this study, mainly based on field experiments, we examined soil water dynamics during spring maize season in MUSL by analyzing observed data for groundwater, soil water content, soil water potential, irrigation, rainfall, evaporation and maize transpiration. The results showed that groundwater clearly hydraulically correlated with soil water. Also significantcorrelations were observed between groundwater and soil water content at different depths, especially at 40–60 cm depth with a correlation coefficient 0.8. Besides, groundwater drawdown lowered soil water stable layer position and weakened hydraulic connections among layers, which limited soil water preservation. Meanwhile increasing maize water demand and declining groundwater table increased vertical variation in soil water content. Based on the field data for soil water content and soil water potential, we noted that the soil water dynamics tracked a curve of weak, strong and weak again during the period from seedling stage to dough stage. Also while about 20 cm soil depth was the main maize water absorption layer, the soil layer of 30–40 cm depth was relatively dry. Irrigation was applied only under water stress. Our study showed that it was possible to determine whether irrigation was needed or not during maize growth by analyzing soil water contents at the 30 cm and 40 cm soil depths. When soil water potential at the 10 cm depth dropped to-0.18 bar, crop physiological processes induced hydraulic lift by maize root. By characterizing soil water dynamics during spring maize season in MUSL farmlands, our study provided essential reference database for agricultural water use along needed theoretical basis for water management in MUSL region.