| To explore the regularity of moisture and temperature and the relationship between moisture and temperature in seasonal freezing and thawing period under different straw mulching treatments, this study was based on the bare land(LD) as contrast and carried on in three kinds of straw mulching methods, 5 cm(J05), 10 cm(J10), 15 cm(J15) whole stalk mulching, whose cover were: 6000 kg/hm2, 12000 kg/hm2 and 18000 kg/hm2. The results showed that:(1) During the freezing and thawing period, the soil underwent three stages, namely initial freezing period, stable freezing stage and thawing period. The results which could be known by comparing the changes of soil moisture during these three periods were: In initial freezing period, LD and treatment groups with different straw mulching had a same change trend of soil moisture content, namely soil moisture content of 0-60 cm profile increased, a high value area appeared at 60 cm profile, soil moisture content of 60-140 cm profile decreased and then soil moisture content of 140-180 cm profile began to rise; In stable freezing stage, soil moisture content of LD decreased from the original 25% to 20% due to soil moisture evaporation in LD. The whole trend of soil moisture content in different treatment groups were basical the same with initial freezing period, but the profile deep of high value area changed, the profile deep of the rest of the treatment groups changed from 60 cm in initial freezing period to 40 cm except the 5 cm straw cover. The whole trend of soil moisture content below 60 cm profile was also basical the same with initial freezing period; After entering thawing period, the soil moisture content in different treatment groups increased due to the melt and infiltration of snow which located in the surface layer and the melt of permafrost and the soil moisture content around 40 cm profile increased to 50%.(2) The average moisture content of J05, J10 and J15 were 2.29%, 3.04% and 1.00% higher than that of the average moisture content in LD in the poly quantity(20-40 cm) by analyzing the average moisture content of LD and different treatment groups, indicating that the effect of J10 on soil moisture was the the most significant and the water retention was the best when experiencing freezing and thawing process and therefore J10 was the best straw mulching treatment. In freezing period, under the best conditions of straw mulching, along with the increase of the profile depth, the difference of the average soil water content from surface to deep(3-5cm, 8-10 cm, 12-15 cm, 20-40 cm, 60-100 cm and 140-180cm)were 3.7%, 4.2%, 5.4%, 2.1%, 0.2% and 0.5%, and the difference were 5.25%, 3.73%, 4.75%, 5.68%, 1.21% and 0.27% in thawing period. The trend of the difference of the average soil water content between J10 and LD appeared to be increasing first and then decreasing, indicating that straw mulching could increase soil moisture, especia lly for the moisture migration of shallow surface soil and surface soil, and less impact on the middle section and lower sections.(3)The trend of the soil average daily temperature of LD was consistent with atmospheric temperature, indicating that atmospheric temperature would influence the changes of the internal temperature of the soil, including soil temperature of 3 cm to 60 cm section was affected most by atmospheric temperature and the influence of 100 cm to 180 cm section by atmospheric temperature was relatively weak. The soil temperature was from low to high when the section was from surface to deep, indicating that the influence of atmospheric temperature was decreasing with the increase of depth profile, and the effects on the surface was strong, on the deep was weak. The hysteresis effect of temperature transmission occured due to straw mulching, as for 12 to 15 cm section, the minimum temperature﹣17 ℃ was reached on January 20, 2014 for LD. The minimum temperature﹣4 ℃ was reached on January 28, 2014 for J05, the minimum temperature ﹣2.6 ℃ was reached on February 22, 2014 for J10 and the minimum temperature﹣2.2 ℃ was reached on March 10, 2014 for J15, fall behind 8 d, 32 d, 50 d as compared with LD, which explaining that during the whole freezing and thawing period, the heat preservation effects were observed in different straw mulching treatments, and the order of heat preservation effects was J15 > J10 > J05 > LD.(4)The influence of various meteorological factors on the soil moisture and t emperature was analyzed by using grey correlation model. Results showed that as for the soil moisture content, soil moisture content of 10 cm profile was mainly affected by factors of evaporation, 180 cm profile was mainly affected by the vapor pressure and environment temperature was the biggest impact on the soil moisture content of the other profiles except the two profiles of 10 cm and 180 cm. As for soil temperature, environment temperature was the main meteorological factors affecting soil temperature of 10 cm, 20 cm, 40 cm, 60 cm and 100 cm profiles, soil temperature of 140 cm profile was mainly affected by factors of evaporation, 180 cm profile was mainly affected by the wind.(5)As for the analysis of the relationship between moisture and heat for the same section depth in LD, the correlation coefficient between soil temperature and moisture content for 10 cm, 20 cm, 40 cm and 60 cm profile were 0.69, 0.67, 0.51 and 0.67, which were positively correlated, indicating that liquid water content decreased with the decrease of the soil temperature. The correlation coefficient between soil temperature and moisture content for 100 cm, 140 cm and 180 cm profile were 0.22, 0.28 and 0.57, which were negatively correlated, indicating that the increase of the hysteresis effect of soil temperature with the increase of the profile depth.In this article, we found out the optimum amount of straw mulching by analyzing of migration of soil moisture and temperature under different straw mulching to provide reference for the rational utilization of soil water resources, establishing reasonable water heat preservation measures and agricultural water saving production. |
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