黄土旱塬区土壤水分状况与作物生长、降水的关系

土壤水分研究是统筹农业生产和生态环境建设的关键环节.本研究结合4年田间定位试验,通过对黄土高原南部长武旱塬冬小麦和春玉米2012—2015年土壤水分状况的研究,分析农田土壤干层形成情况、土壤水分对作物生长的影响、降水对土壤水库的影响以及作物对土壤水分状况的影响.结果表明: 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;相较于春玉米,冬小麦根系生长习性更符合黄土旱塬区土壤水分循环特征,黄土旱塬区土壤水分有效性可保证作物产量稳定;降水作用下,冬小麦土壤水库充、放水过程呈现收获期、休闲期和苗期连续充水、缓慢消耗期和大量消耗期连续失水相互交替的特点.0～300和300～600 cm土层土壤水库不一致性现象明显,以最大根深作为野外监测试验中土壤含水量的取样深度时,由于深层土壤水库负反馈作用,不同降水年型下,休闲期和苗期的蒸散均会被高估,缓慢消耗期和大量消耗期的蒸散均会被低估.冬小麦田间过渡层存在的范围为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.

Relationship between soil moisture dynamics,crop growth and precipitation in rain-fed area of the Loess Tableland,China.

Studying soil water dynamics is critical to agricultural production and ecological environment construction. Based on a 4-year field experiment, we measured soil moisture in both winter wheat and spring corn fields in rain-fed Changwu Tableland of the Loess Plateau from 2012 to 2015, explored soil desiccation and analyzed the effects of soil moisture on crop growth, the effect of precipitation on soil reservoir, and the effect of crop on soil water dynamics. The results showed that the dominant factor for the formation of dried soil layer was yearly precipitation pattern in winter wheat field and was uneven distribution of precipitation among months in each year in spring corn field. Permanent dried soil layer did not occur in both winter wheat and spring corn under the plan-ting system of one crop a year in rain-fed Changwu Tableland. Due to the characteristics of soil water circulation in the Loess Tableland, planting winter wheat was more suitable for this region compared to spring corn. Soil water availability in the Loess Tableland area could ensure the stability of crop yield. Under the influence of precipitation, soil reservoir in winter wheat was consecutively recharged from harvest period to fallow period to seedling period, while from slow consumption period to large consumption period, soil reservoir was consecutively consumed. Soil reservoir in the depth of 0-300 and 300-600 cm was inconsistent. If the maximum root depth was used as sampling depth when measuring soil moisture, evapotranspiration would be overestimated in the fallow period and the seedling period, but would be underestimated in the large consumption period and slow consumption period. This was mainly due to the negative feedbacks of deep soil reservoir. In winter wheat field, transition layer existed and ranged from 140-360 cm. Crop growth at different stages had an effect on soil reservoir. Soil reservoir showed inter-annual regulation effect on the water supply to winter wheat and intra-annual regulation effect on spring corn.