Study On Soil Water And Temperature Characteristics In The Dormant Period Of Jujube In Loess Plateau Regions In Northern Shaanxi

Loess hilly region of Northern Shaanxi Province is a typical semi arid climate region,with less rainfall and strong evaporation. The jujube forest and bare land in the Loess Hilly Region are for the study. One hand, we discussed the spatial and temporal variation of soil moisture in the whole year and the non reproductive period of jujube, on the other hand, we discussed the law and reason of water movement in the bare and covered shallow soil, and evaluated the effect of film mulching measures to retain moisture in soil. At last, the water movement and temperature in the bare and covered shallow soil were simulated by hydrus-1D model to provide a theoretical basis for the water retaining measuresin the non reproductive period of jujube of different years. The main conclusions are as follows:( 1) The change of soil moisture within 1000 cm depth throughout the year can be divided into three layers: variable layer( 0-250cm),difficultly changing layer( 250-750cm) and stabilizing layer( 750-1000cm). soil moisture of variable layer ranged between 6.39% and 12.83%, and soil water storage ranged between 148 mm and 235 mm.The soil water storage of difficultly changing layer ranged between 391 mm and 460 mm, and the soil water storage of stabilizing layer ranged between 240 mm and 268 mm. With the increase of soil depth, the soil water storage is increasing and the seasonal variation of soil moisture decreases rapidly. In addition, the change of the deeper soil moisture has a certain lag.(2)soil water loss mainly occurred in the shallow soil in the dormant period of jujube,and the 50 cm soil moisture loss of bare and jujube land accounted for 47.5% and 52.8% of the moisture loss in the 1000 cm soil layer, respectively, the 50-340 cm soil moisture loss of bare and jujube land accounted for 34.5% and 35.2% of the moisture loss in the 1000 cm soil layer,respectively,the 340-1000 cm soil moisture loss of bare and jujube land accounted for 18% and12% of the moisture loss in the 1000 cm soil layer, respectively. The water consumption mainly comes from the natural evaporation of soil. The october soil moisture was the highest value in the dormant period. The soil moisture decreased rapidly from the early october to the time when the soil freezed. When the soil freezed, deep soil temperature was higher than shallow soil temperature, the soil moisture began to migrate from deep soil to shallow soil,and the shallow soil moisture began to rise until the soil thawed. Soil moisture in the 0-60 cm soil layer decreased from 8.93% to 11.4% through the whole period of non growth., and the60~200cm soil moisture is basically stable with the average value of 7.03%.(3)The temperature gradient is one of the important factors that lead to the change of soil moisture, and the heat of the soil is mainly from the solar radiation. The effect of solar radiation on the soil temperature reaches the depth of 50 cm below the soil layer.In the sunny days, bare soil temperature showed a diurnal variation trend of sine, and the diurnal amplitude of soil temperature decreases with the increase of the depth of the soil layer, and the maximum temperature and the minimum temperature appear gradually.In two different conditions, the value of soil temperature time lag than bare land, and black film laged behind the white film. Diurnal amplitude of soil temperature and daily maximum temperature were white film >bare land>black film, and the daily minimum temperature was black film >white film >bare land. The ground temperature and air temperature showed a significant linear relationship, and with the increase of soil depth, the correlation was gradually weakened.(4)During the growing period of jujube with less rainfall, The soil moisture decreased with rising soil temperature. Plastic sheeting can effectively inhibit the evaporation of soil moisture loss, and the average rate of soil moisture evaporation loss, bare> White Film>Black Film. When the soil is not frozen in the dormant period of jujube, the soil moisture is lower with less rainfall. Soil moisture evaporation has a weaker sensitivity to soil temperature.Soil temperature and soil moisture showed a downward trend, Wherein the moisture rate of decline bare> White Film> Black Film. Soil water storage in 0-50 cm soil layer decreased by7.34 mm, and soil water storage under white and black film coating conditions decreased by4.85 mm and 4.02 mm.(5)The model of Hydrus-1D could better simulate the soil moisture dynamic changes of bare land and black film treatment in non reproductive period, and provide a theoretical basis for the moisture conservation measures of non reproductive period in different years.