黄土旱塬区麦田休闲期降水与土壤贮水的变化特征

为提高休闲期降水资源利用效率和确保区域粮食安全,利用1981—2020年陇东黄土高原旱作麦田定位土壤水分和气象观测资料,分析了冬小麦田休闲期间降水与土壤水分的变化特征及其影响因素。结果表明:(1)近40年陇东黄土高原休闲期降水以14 mm/10 a的速率增加,降雨总日数和小雨日数呈减少趋势,中雨、大雨日数呈弱增加趋势;(2)近40年休闲期1 m土层平均以9.5 mm/10 d的速率充水,贮水量平均增加97 mm,21世纪以来贮水量增加明显;(3)休闲期降水与1 m土层贮水增量符合二次函数关系,1 m土层开始贮存水分的降水阈值为175 mm,贮水增量与中、大雨总日数相关性最高,前期降水主要以土壤蒸发消耗为主,后期降水则大部贮存于土壤中;(4)休闲期1 m土层平均贮水效率为0.27,贮水效率随着麦收时的土壤墒情增加而线性递减,当麦收时1 m土层贮水量小于田间持水量的45%～48%时,贮水效率较高,1 m土层水分得到充分补充的降水阈值为388 mm。该研究成果揭示了近40年陇东黄土高原休闲期降水和土壤贮水的转化规律,同时为指导区域水资源高效利用提供科学依据。

Variation Characteristics of Precipitation and Soil Water Storage in Winter Wheat Field During Fallow Period in Rainfed Area of the Loess Plateau

In order to improve the utilization efficiency of precipitation resources in fallow period and ensure regional food security, we collected the soil moisture data of winter wheat fields and meteorological observation data from 1981 to 2020 to analyze the variation characteristics of precipitation and soil moisture in rainfed area of the Longdong in the Loess Plateau. The results showed that:(1)in the past 40 years, the precipitation during the fallow period of the Longdong in the Loess Plateau increased at a rate of 14 mm/decade, but the inter-annual difference was large; the numbers of rainfall days and the light rain days decreased, while the number of moderate and heavy rain days showed a slightly increasing trend; the increase of rainfall intensity had a greater contribution to the increase of precipitation;(2)the obvious water-filling process in 1 m soil layer was observed in the fallow period, increasing at a rate of 9.5 mm/10 days, and the average water storage capacity increased by 97 mm in the past 40 years; the increment of water storage was the lowest in the 1990s, but it increased significantly since this century;(3)there was a quadratic function relation between the precipitation and the soil water storage in 1 m soil layer during the fallow period; the precipitation threshold of 1 m soil layer starting to store moisture during the fallow period was175 mm; the water storage increment had a high correlation with the total days of moderate and heavy rain; early precipitation during the fallow period was mainly consumed by soil evaporation, and most of the precipitation in the later period was stored in the soil;(4)in recent 40 years, the average soil water storage efficiency of 1 m soil layer was 0.27 for winter wheat fields during the fallow period, and the water storage efficiency decreased linearly with the increasing of soil moisture during winter wheat harvest; when the water storage of 1 m soil layer during wheat harvest was less than 45%～48% of the soil water holding capacity, the water storage efficiency was higher; there was also a quadratic function relation between precipitation and soil water storage efficiency during the fallow period, and the precipitation threshold for soil moisture fully supplemented in 1 m soil layer was 388 mm. This study reveals the transformation processes of precipitation and soil water storage in the fallow period in Longdong of the Loess Plateau in the past 40 years, and provides a scientific basis for guiding the efficient utilization of regional water resources.