KMS Institute of soil and water conservation Chinese Academy of Sciences
|Place of Conferral||北京|
|Keyword||黄土塬区 旱作农业 水量平衡 土壤水库 蒸散 土壤干层|
（1）冬小麦田间年均土壤含水量垂直分布曲线均呈“双峰双谷”形，第一处峰点在10～20 cm土层，第一处谷点在50 cm左右，第二处峰点在100 cm左右，第二处谷点在280 cm左右。无论何种降水年型下，土壤水库对降水的响应滞后且滞后的程度一致。降水年型对土壤水库的年际与年内动态变化影响较大。与丰水年相比，枯水年、平水年土壤水库对大气干旱的调节能力降低，表现为主要供水层上移；枯水年、平水年降水量虽少，但对土壤水分的补充作用较丰水年明显；丰水年土壤水库有较大盈余（84.2 mm），水分平衡出现正补偿，枯水年土壤水库稍有亏缺（1.5 mm），水分平衡出现负补偿，平水年土壤水库稍有盈余（9.5 mm），水分平衡出现正补偿.长武旱塬冬小麦田间土壤水分动态可分为4个时期：苗期耗水期、缓慢消耗期、大量消耗期、收获期，整体蒸散耗水大小顺序为：大量消耗期>苗期耗水期>收获期>缓慢消耗期。
（2）春玉米田间年均土壤含水量垂直分布曲线均呈“单峰单谷”形，峰点在10～20 cm层，谷点在50 cm左右，70～100 cm层土壤含水量常年较稳定。与丰水年相比，枯水年春玉米生长期田间土壤水库对大气干旱的调节能力降低，表现为主要调节深度上移变浅；枯水年春玉米生长期田间土壤水分比丰水年稳定。两种降水年型下土壤水库“水位”均呈现先上升后下降再上升的特点。枯水年土壤水库有较大亏缺，第2季亏缺为94.3 mm，第4季为123.7 mm，水分平衡均出现负补偿；丰水年土壤水库有较大盈余（208.6 mm），水分平衡出现正补偿。春玉米和冬小麦生长期蒸散耗水的水分来源不同，对于冬小麦，一部分是生长期降水，另一部分是休闲期降水，即休闲期土壤储水；对于春玉米，丰水年时，只有生长期降水，枯水年时，一部分是生长期降水，另一部分是上一季土壤储水。
（3）运用农田水量平衡有效划分了生长期作物蒸散耗水和休闲期无效蒸散，冬小麦生长季多年蒸散均值约为540.8 mm，其中，休闲期无效蒸散均值约为103.2 mm，占年蒸散的19.1%；春玉米生长期多年蒸散均值为547.0 mm，休闲期无效蒸散均值为136.8 mm，占比25.0%。长武塬区冬小麦和春玉米蒸散水平相当，休闲期无效蒸散均较高。冬小麦生长季蒸散呈较明显的双峰曲线分布，春玉米生长季蒸散呈较明显的单峰曲线分布。该区冬小麦土壤能保持良好的水分生态环境，比春玉米更适合长武旱塬区发展旱地农业。
（4）降水年型是冬小麦地土壤干层形成的主导因素，年内降水分布不均是春玉米地土壤干层形成的主导因素。长武旱塬区冬小麦和春玉米一年一季的种植制度不会导致永久性干层的产生。冬小麦土壤水库充放水过程呈现收获期、休闲期与苗期连续充水和缓慢消耗期与大量消耗期连续失水相互交替的特点。0~300 cm土层和300~600 cm土层土壤水库不一致性现象明显，若以最大根深作为野外监测试验中土壤含水量的取样深度，由于深层土壤水库负反馈作用，不同降水年型下，休闲期与苗期蒸散均会被高估，缓慢消耗期与大量消耗期蒸散均会被低估。冬小麦田间过渡层存在，范围约为140~360 cm。作物生长的时间跨度影响土壤水库效应的发挥，土壤水库对冬小麦供水表现为年际间的调节作用，土壤水库对春玉米供水表现为季节间的调节作用。
|Other Abstract||Based on long-term field experiments, we investigated dynamics of soil reservoir and evapotranspiration in dry farmland by studying the dynamic change of soil moisture in both winter wheat and spring corn field in the rain-fed Changwu Tableland. Meanwhile, we clarified the water sources for evapotranspiration during the growing period of spring corn and winter wheat, assessed the water balance of the farmland ecosystem, and obtained a preliminary understanding of the formation and recovery process of the dried soil layer, which provided data support and theoretical basis for the production practice and sustainable development of dry farming. The study presented here had the following conclusions:|
（1）The vertical distribution of annual average soil water content in winter wheat field were "double peaks and double valleys": first peak and valley occurred in the 10-20 and 50 cm soil layer, respectively, while for the second peak and valley, corresponding soil layer was the 100 and 280 cm soil layer. Soil reservoir did not coincide with precipitation for all yearly precipitations patterns but lagged behind. Annual precipitation patterns had a great influence on the inter-annual and annual dynamics of soil reservoir. Compared with rainy year, the depth of soil moisture consumption decreased in both drought year and normal year and the supplement of precipitation to soil moisture was lower. In rainy year, soil reservoir had a large surplus (84.2 mm); while in normal and drought year, corresponding values were 9.5 and -1.5 mm, respectively. Therefore, we could infer that soil reservoir was compensated in both rainy year and normal year, while in drought year soil reservoir was consumed. In our study, dynamics of soil water in winter wheat field could be divided into four periods: seedling period, slow consumption period, large consumption period, and harvest period and the order of evapotranspiration were large consumption period> seedling period> harvest period> slow consumption period.
（2）The vertical distribution of annual average soil water content in spring corn were "single peak and single valley": peak and valley occurred in the 10-20 and 50 cm soil layer, respectively, and soil water content in 70-100 cm soil layers was relatively stable. Compared with rainy year, root uptake depth decreased in drought year and the soil water content was more stable. The "reservoir level" in both precipitation patterns showed as followings increased firstly, then decreased, and rised again. In drought year, soil reservoir had a large deficit, while for the second and fourth season, corresponding values were 94.3 and 123.7 mm, respectively; while in rainy year, it had a large surplus (208.6 mm). Thus, we could infer that in rainy year water balance was compensated, while in drought year water balance was negatively compensated. The water sources of evapotranspiration during the growing periods differed in both winter wheat and spring corn. For winter wheat, water source of evapotranspiration was consisted of growth period precipitation and fallow period precipitation; while for spring corn, water resource differed in rainy and drought years. Water resource was only precipitation during the growing period in rainy year, while in drought years, water source was consisted of growth period precipitation and soil water storage of last season.
（3）Evapotranspiration of farmland could be divided into two parts: actual evapotranspiration during the growing period and invalid evapotranspiration during the dormant period . Growing seasonal mean evapotranspiration of winter wheat was about 540.8 mm, and invalid evapotranspiration accounted for 103.2 mm. For spring corn, these corresponding values were 547.0 and 136.8 mm, respectively. Evapotranspiration of winter wheat and spring corn was the same, and large evapotranspiration losses during the fallow period. The distribution of evapotranspiration during the growing period was single peak in both winter wheat and spring corn field. Winter wheat is more suitable than spring corn for the development of dryland agriculture in rain-fed Changwu Tableland.
（4）Yearly precipitations pattern is the dominant factor of dried soil layer formation in winter wheat field, and the uneven distribution of precipitation during the year is the dominant factor in the formation of dried soil layer in spring corn field. The cropping system of winter wheat and spring corn in rain-fed Changwu Tableland will not result in permanent dried soil layer. The process of filling and releasing water in winter wheat soil reservoir presents the characteristics of alternating water filling during large consumption period and slow consumption period, and continuous loss of water during harvest period, fallow period and seeding period. Soil reservoir in the depth of 0 -300 cm and 300-600 cm was obviously inconsistent. So if the maximum root depth was used as sampling depth when measuring soil moisture, evapotranspiration during fallow period and seedling period will be overvalued and that during large consumption period and slow consumption period will be underestimated because of negative feedback effect in deep soil reservoir. Transition layer exists in winter wheat field, ranging from 140-360 cm. Time span of crop growth had an effect on the soil reservoir. For example, winter wheat consumed the fallow soil water storage to meet crop needs in the next year, and spring corn utilized the soil water storage to offset crop water shortage that caused by seasonal atmospheric drought or uneven distribution of precipitation.
|李鹏展. 黄土塬区旱作农田土壤水库动态及蒸散规律[D]. 北京. 中国科学院研究生院,2018.|
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