| Songnen Plain is one of the most important food production bases in China.However due to uneven distribution of water and soil resources,low utilization rate of irrigated water,and serious waste and pollution of water resources,make the water resources shortage in Songnen Plain more serious.Drought has become an important factor restricting the economic development in the Songnen Plain.Therefore,how to utilize soil and water resources efficiently and improve the utilization efficiency of water resources has become an urgent problem that needs to be solved.Straw mulching,as the most common way of farmland management in the north of China,can effectively reduce the evaporation of soil moisture and keep the soil moisture.This paper is aimed at the seasonal frozen soil area in the Songnen Plain.Four treatments of bare land,4500 kg/hm~2 straw mulching,9000 kg/hm~2 straw mulching and 13500 kg/hm~2 straw mulching were carried out in thawing period.The changes of soil freezing depth,soil liquid water content,soil temperature,soil evaporation and infiltration were observed.Based on the measured data,the effects of different straw mulching on soil freezing depth,soil liquid water content,soil temperature,soil evaporation and infiltration were analyzed by Mallat algorithm,information coefficient and statistical analysis method.The main conclusions are as follows:(1)Soil thawing occurred at both the top and the bottom of the frozen soil layer.Although the bottom of the frozen soil layer began to thaw first,the rate at which the surface soil thawed was greater.The thawing rate of the surface soil was about four times that of the bottom of the frozen soil layer.The straw is low thermal conductivity,which hinders the transmission of heat from the atmosphere to the soil,and as the amount of coverage increases,the hindrance effect is gradually obvious.During the thawing period,the straw mulching could postpone the time of the thawing of the surface frozen soil,delay the thawing rate of the surface frozen soil,and postpone the time of total thawing of the frozen soil.The total thawing time of BL treatment was 3-6 d earlier than that of other three treatments.Straw mulching did not affect the thawing rate of the underground frozen layer.(2)The soil liquid water content of each treatment during the whole thawing period was gradually increased first and then gradually decreased after reaching the peak value.During the thawing period,straw mulching could delay the peak time of soil liquid water content,increase soil liquid water content and reduce the range of soil liquid water content.In the 10cm soil layer,the soil liquid water content of BL was 2.50-6.00%lower than that of the other three treatments,and the range was 5.20-6.10%smaller than that of the other three treatments.The peak time of soil liquid water content of BL was 2-5 d earlier than that of the other three treatments.With the increase of soil depth,the change of soil water content decreased gradually,and the effect of straw mulching on soil water content decreased gradually.On March 10,the water content of soil liquid in the BL treatment showed an increasing trend with the increase of soil depth.On March 21 and April 2,the soil liquid moisture content of BL was presented as"S"with the increase of soil depth.On April 14,soil liquid moisture content of BL increased gradually with soil depth.(3)The soil temperature of each treatment in the thawing period showed a slow increase and then a dramatically rise with fluctuation.The straw mulching could reduce the change of soil temperature.The range of soil temperature in 10cm soil layer of BL,SM1,SM2 and SM3 were 0.13-14.56?,-0.13-7.69?,-1.44-6.13?,and-1.75-5.00?,respectively.With the increase of soil depth,the change of soil temperature gradually decreased.In the BL treatment,the range of soil temperature in 10cm-100 cm was 14.43?,8.88?,6.75?,5.88?,5.06?,4.44?,3.88?,3.31?,2.75?,and 2.25?,respectively.In March 10th,the soil temperature of BL showed a slight increase and then decreased gradually.In April 14th,the soil temperature of BL showed a trend of decreasing sharply first and then increasing slowly.Similar results appeared in SM1,SM2 and SM3.In March 21st,the change of the temperature of soil profiles in four treatments was minimal.In April 2nd,the change of the temperature of soil profiles in BL and SM1 was maximal.In April 14th,the change of the temperature of soil profiles in SM2 and SM3 was maximal.(4)During thawing period,the straw mulching could inhibit soil evaporation,and as the amount of straw mulching increased,the inhibitory effect was more obvious.The cumulative evaporation of SM3at thawing period was 7.4 mm,4.8 mm and 2.9 mm less than that of BL,SM1 and SM2.In the early stage of soil thawing,the daily soil evaporation of BL was larger than that of other three treatments.However,in the late stage of soil thawing,the soil evaporation of BL was smaller than that of other three treatments.The variation trend of soil daily evaporation in BL was unchanged and then gradually decreased.The trend of daily evaporation of other three treatments increased first and then decreased.During the thawing period,straw mulching could reduce the variation range of daily evaporation,inhibit the change of daily evaporation and reduce the effect of random factors on soil daily evaporation,and as the amount of straw mulching increased,the effect was more obvious.The soil liquid moisture content and vapor pressure were main factors that affect soil evaporation in the thawing period.(5)During the thawing period,the infiltration process of each treatment was basically the same.When infiltration began,soil infiltration increased rapidly.As time went on,soil infiltration increased slowly,until stable infiltration finally reached.With the soil thawing,the soil initial infiltration rate,the steady infiltration rate and the cumulative infiltration amount gradually increased.During the thawing period,the straw mulching could reduce the initial infiltration rate,the steady infiltration rate and the cumulative infiltration amount.The effect of surface soil temperature on soil infiltration was significantly higher than that of deep soil temperature.The effect of surface soil temperature on soil stable infiltration rate and cumulative infiltration amount was mainly divided into three stages:when the soil temperature was lower than 0?,with the increase of soil temperature,soil stable infiltration rate and cumulative infiltration amount increased slowly.When the soil temperature reached around 0?,soil stable infiltration rate and the cumulative infiltration amount increased rapidly with the increased of soil temperature.When the temperature was higher 0?,soil stable infiltration rate and cumulative infiltration also increased slowly with the increase of soil temperature. |
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