Dynamic Characteristics Of Soil Water And Heat And Their Interaction Mechanisms Under Plastic Membrane + Geotextile Cloth Mulching

This field experimental study was carried out at the eastsouth egde of Mu Us sandy land on the soil water retention sand belt,for a period of 1 year.With the sand surface first reshaped into furrow-and-ridge form,the in-situ field test had 3 treatments,i.e.,the ridge section one was covered with plastic membrane plus weed-blocking geotextile(MB);section two covered with weed-blocking geotextile only(DB);and section three exposed or uncovered to serve as the blank contrast(CK).soil moisture content,soil water potential and temperature at 0 to 20 cm and 0 to 30 cm depths below the soil surface,as well as surface meteorological parameters,werecontinuously monitored to understand the dynamic water and heat characteristics and their interaction mechanisms under plastic membrane + geotextile ground cover conditions.The main results are as follows:(1)The MB cover resulted in higher annual average temperatures at 5,15,30 cm of soil depths,being 0.5,0.6,and 0.5 ℃ higher,respectively,than that under the DB cover which is 1.0,0.8,and 1.0 ℃ higher than the CK condition.At the same depth,the length of the freezing-thawing period was longest for CK,intermediate for DB,and shortest for the MB.There was a significant difference in soil temperature between the three treatments at the same depth(P<0.05),and the soil heat conservation effect was the best under MB;2)At 5,15,30 cm soil depths,the accumulated,no less than 5 ℃ soil temperature,under MB is respectively 4%,4% and 3% higher than that of DB which was respectively 8%,7% and 9% higher than that under CK.(2)The daily variations of soil water potential under the 3 treatments all showed characteristics of a Cosmic function.The daily soil water potential at the 5 cm depth was the most varied in the three groups,varying between-600 and-120 KPa,and showing MB>CK>DB.At the 15 cm depth,the value was higher with smaller variation between-180 and-90 KPa,showing DB>CK>MB.At the 30 cm depth,the soil water potential is virtually stable,with high water potentials for MB and DB stabilized at about-100 KPa,and much lower stable potentials for CK at about-285 KPa;The annual variation of soil water potential showed two valleys,including the freezing-thawing period in the winter and the strong evaporation period in the summer.The annual averages among the 3 groups show that: at 5 cm MB>CK>DB,at 15 cm DB>CK>MB,and at 30 cm MB=DB>CK,the mean value of soil water potential at 0-30 cm was MB>DB>CK.(3)In the 0-10 cm soil layer,the curve of soil moisture content under the mulched conditions(MB and DB)fluctuates strongly,and the coefficient of variation is 0.44.In the 10-20 cm soil layer,the fluctuation of MB treatment was the strongest,followed by CK,and the weakest in DB,and the coefficient of variation was 0.33,0.28,and 0.24,respectively.The average soil moisture content and water storage volume in the 0-20 cm soil layer under each treatment showed MB>DB>CK,and the monthly average soil moisture content showed a variation pattern of "double peaks and double valleys".In the 0-20 cm soil layer,the soil water storage in summer and autumn was larger than MB,followed by DB,and smaller than CK.In spring,the soil water storage in MB was close to DB and higher than CK.The maximum increase of soil water storage in spring was DB,the maximum increase in summer was MB,the maximum increase in winter was CK,and the maximum decrease in soil water storage in autumn was MB.(4)The effect of typical rainfall on soil temperature and water content is as follows: Before,during and after a rainfall event,the daily range of soil temperature at the same depth is the largest in MB,followed by DB,and the smallest in CK.In the 0-20 cm soil layer,the mulched treatments(MB and DB)significantly raised the soil moisture content in the furrows.The response of soil water to small rainfall was the fastest in MB,followed by DB,and CK was the slowest.(5)Gray correlation method and other methods were used to analyze the influence of meteorological factors on soil water and heat.In the freezing-thawing period of 0-30 cm soil layer,rainfall and dew had a greater influence on soil water potential and temperature,while atmospheric temperature had a greater influence on soil warmth but a smaller influence on soil water potential.In the non-freezing-thawing period,atmospheric temperature and humidity have a great influence on soil temperature,but the influence on soil water potential is less.(6)During the freezing period,the coupling effect of soil water potential and temperature was better under CK treatment at 5 cm and 30 cm,followed by DB,and worst in MB.The coupling effect was poor under the mulching condition at the 5 cm soil layer,while better under the mulching condition at the 15 cm and 30 cm soil layer.During the thawing period,at the 5 cm soil layer,the coupling effect of soil water and heat under the 3 groups were not significantly different.With the increase of depth,the coupling effect of water and heat gradually strengthened.At 5 cm and 30 cm soil layer,the coupling effect of MB is better than that of the DB and CK,and at 15 cm soil layer,MB and DB treatments arepoorer compared to CK treatment conditions.