Experimental Study On Dynamic Changes Of Soil Moisture And Temperature Under Different Combinations Of Water And Nitrogen And Surface Coverage During Seasonal Freeze-thaw Period

In the seasonal freeze-thaw soil distribution area,the freezing and melting of water in the soil system and the change of soil temperature were always accompanied by the physical process of water heat exchange between the ground gas.In order to reveal the temporal and spatial variation of water and heat of soil under different irrigation-fertilization and surface coverage in seasonal frozen soil area,the field experiments of surface cover and irrigation-fertilization were carried out in Dongyang experimental area,Jinzhong,Shanxi.The surface covered 3 kinds of corn straw mulching?JG?,polythene transparent film mulching?DM?of 0.1mm,and bare land?LD?of natural coverage?LD?.Three fertilization rates?100,300 and 500 kg/hm²?and two irrigation water?375,750 m³/hm²?were set up in the winter irrigation experiment,and 6 kinds of irrigation-fertilization combinations were formed and compared with those of the no irrigation plots.By means of mathematical statistics and grey correlation analysis,the dynamic changes of soil moisture and heat with time in different thaw processes were statistically analyzed.In order to explain the distribution of moisture and temperature in the soil profile during seasonal freeze-thaw period,the law of water and heat migration and transformation in the soil system was revealed.It provided a basis for determining the winter and spring irrigation technology parameters and the effective utilization of soil water-fertilizer resources for irrigation and fertilizer integrated irrigation area in northern China.?1?winter irrigation-fertilization test?Irrigation-fertilization affected the dynamic change of soil profile temperature during freeze-thaw period.In the freeze-thaw stage,the soil temperature at the surface of the irrigation-fertilization plots were lower than that of the irrigated plots,and the ground temperature showed a"high low high"distribution trend on the soil profile.The effect of irrigation-fertilization on soil temperature was different in different freeze-thaw stages.During the unstable freezing period,the soil temperature of irrigation-fertilization plots0-10cm was at a low level.In the early stage of stable freezing,the ground temperature of0-30cm rised obviously and changed greatly,and the 30-150cm ground temperature changed little.In the later stage of stable freezing,the specific heat capacity of soil increased,and the soil temperature changed more slowly than that in the early stage of stable freezing.During the ablation stage,the temperature of the soil increased to the outside temperature,and the0-30cm soil temperature increased to varying degrees.During the whole freeze-thaw period,the 0-20cm soil temperature fluctuated greatly,and the 30-90cm soil temperature changed slowly.The average temperature of 0-30cm soil in the whole freeze-thaw period were higher than that of N₀W₀ under W₇₅₀ treatment,while W₃₇₅ treatment had no obvious effect on soil temperature.The soil temperature in 30-150cm was not increased with the increase of the amount of irrigation-fertilization,and the effect of N₃₀₀W₃₇₅ and N₅₀₀W₇₅₀ on the temperature of 30-150cm soil was better,and the higher the irrigation amount was,the more obvious the effect was.The absolute grey correlation degree?0.791⁰.977?of 0-20cm between soil temperature and N₀W₀ treatment was higher than that of 30-90cm?0.960⁰.995?,the combination of irrigation-fertilization had great influence on 0-20cm soil temperature,and had little effect on 30cm.?Irrigation-fertilization affected the dynamic change of soil profile during freeze-thaw period.The surface before frozen and irrigation plots compared with N₀W₀ plots with high moisture content.In the early stage of stable freezing,the high value area of soil moisture was20-50cm.At 40cm,N₅₀₀W₇₅₀ and N₃₀₀W₃₇₅ had higher water holding peak value.Stable freezing stage,soil moisture in the high value area expanded to 60cm,the peak volume extended to 50cm poly entropy.After frozen layer ablation,the storage capacity of N₃₀₀ and N₅₀₀ treated at 0-60cm was lower than that of N₀W₀ treatment.During the whole freeze-thaw period,the effect of winter irrigation-fertilization on 0-20cm increased gradually with the increase of soil depth.At 30-40cm,the peak value of irrigation-fertilization plots were higher than that of N₀W₀.In ablation stage,N₅₀₀W₇₅₀ and N₃₀₀W₃₇₅ treatments were helpful to test soil water storage effect.At 50-60cm,N₃₀₀ had larger peak moisture content under W₇₅₀ and W₃₇₅ treatments.The absolute grey correlation degree of soil moisture content of the irrigation-fertilization plots and the N₀W₀ tillage layer?0-20cm?were?0.5261⁰.719?,and the absolute grey correlation of soil moisture content of 30-110cm were?0.6168⁰.9961?.Water conservation effect of different combination of irrigation water in the depth of 0-20cm was better,while below 30cm soil moisture effect.?2?Surface cover test?Surface coverage affected the dynamic change of soil profile temperature.Surface cover weakened the heat exchange between air and soil,delayed the freezing time and freezing depth of soil,and changed the natural freezing and thawing process of soil.Plastic film mulching had a significant warming effect on the soil layer.Straw mulching had different effects on soil temperature in different freeze-thaw stages:in the freezing stage,straw mulching reduced soil heat loss and increased soil temperature.During the melting stage,straw mulching weakened the heat exchange between the ground and the atmosphere,and inhibited the increase of soil temperature.Mulch and straw mulching could stabilize the amplitude of soil profile.During the whole freeze-thaw period,the soil temperature was affected by two kinds of covering treatment.The influence of 0²0cm on soil temperature was greater.The soil temperature of 20⁹0cm increased with the soil depth,and the fluctuation amplitude of soil temperature gradually decreased.?Land cover affected the dynamic change of soil profile.Surface mulching effectively reduced the evaporation of surface soil moisture and weakened the fluctuation range of soil moisture content.However,soil moisture in different land surface covered plots varied with freeze-thaw stage:compared with the LD,the freezing stage,JG and DM significantly increased the 0¹0cm of soil moisture,soil moisture of DM was better than JG;The melting period,straw mulch prevented snowmelt water infiltration,water conservation effect of JG on soil was not obvious;In the later stage of melting,straw mulching weakened the influence of wind speed on the surface soil moisture,inhibited the evaporation of surface soil,and had the function of soil moisture conservation for soil layer.The freeze-thaw period,DM always had a water retention effect on soil moisture,and its effect was better than that of JG.Surface coverage effectively weakens the fluctuation amplitude of soil water content in0²0cm.With the increase of soil depth,the impact of coverage measures on soil moisture content changed gradually weak.The absolute grey correlation degree?0.6559⁰.9083?between JG and LD in soil profile of 0⁸0cm was lower than that of DM?0.7392⁰.9911?.It showed that the change trend of DM soil moisture over time was similar to that of LD.