Effects Of Freezing And Thawing On The Physical And Chemical Properties Of Soil At Different Altitudes In The Alpine Regions Of Western Sichuan

Kangding Mountain zhe Duo belongs to the western sichuan alpine region,located in the western sichuan province,east of the qinghai-tibet plateau,belong to the first level terrain ladder transition zone of the ladder to the second terrain,soil environmental change is the most vigorous area,belongs to the typical fragile ecological environment area.The area has important significance in regional climate regulation,stable ecological environment in the upper reaches of the Yangtze river,water conservation and soil conservation.To kangding SheDuoShan as the research object,this paper uses the method combining the field investigation and indoor simulation,the study of western sichuan alpine mountain freezing and thawing process of soil nutrients under different processing conditions and the influence of the structure,to reveal the western sichuan alpine mountain changes in seasonal frozen soil structure and fertility,as well as the mechanism of changes of soil physical and chemical properties under freezing and thawing stress and soil material migration into significant,but also for other alpine mountain provide theoretical basis for the governance of freezing and thawing erosion.The main conclusions are as follows:(1)Before and after freezing and thawing,the soil organic carbon content was lower than that of CK.Before and after simulating freeze-thaw,the oxidizable organic carbon of the treated soil was decreased compared with that of CK,but it was generally higher than that of CK..With the decrease of altitude,the content of soil organic carbon showed a slight increase and then a sharp decrease.The content was the lowest at an altitude of 3400 m.In the treatment of time and temperature,with the increase of time and the decrease of temperature,all the altitudes The content of soil organic carbon and easily oxidized organic carbon showed a trend of increasing or decreasing,and the difference was not significant(P>0.05).In the treatment of water content,with the increase of water content,the soil organic carbon content generally showed a trend of increasing first and then gradually tending to be steady,and the content of soil oxidizable organic carbon showed an increasing trend in general.(2)Before and after simulated freezing and thawing,the ammonium nitrogen content of the soil at all altitudes was generally higher than that of the CK without freezing and thawing.The content of alkaline dissolved nitrogen in the soil was lower than that of CK.With the decrease of altitude,the content of ammonium nitrogen showed a trend of decreasing gradually after first increasing gradually.The content was the lowest at 3400 m,and the content was highest at 4200 m;the content of alkaline dissolved nitrogen showed a decreasing trend.The content is the lowest at 3400 m above sea level and the highest at 3800 m above sea level.In the simulation of freezing and thawing time and water content treatment,with the increase of time and moisture content,the ammonium nitrogen content showed a trend of increasing and decreasing.In the temperature treatment,the ammonium nitrogen content showed an overall change.Trends;During the treatment of time,the content of alkali-hydrolyzed nitrogen generally showed a downward trend with increasing time.In the treatment of temperature and moisture content,the content of alkali-hydrolyzable nitrogen increased with the decrease of temperature and the increase of water content.There is a decrease.(3)Before and after simulating freeze-thaw cycles,the available soil phosphorus content at all altitudes showed an increasing trend compared with CK values.In the time treatment,with the increase of time,the available phosphorus content in soil increased and decreased;in the temperature treatment,with the decrease of temperature,the available phosphorus content in the soil showed an overall change trend;in the treatment of water content,With the increase of water content,the available phosphorus content generally shows a decreasing trend.(4)Before and after simulated freezing and thawing,the available potassium content in soils at various altitudes showed an increasing trend compared with that of CK.With the decrease of altitude,the available potassium content generally showed a gradual decrease,and then suddenly increased at an altitude of 3400 m,among which the available potassium content was the lowest at 3600 m.In the simulated freeze-thaw time and temperature treatment,With the increase of time and the decrease of temperature,the content of soil available potassium showed a trend of increasing or decreasing.In the treatment of water content,the content of soil available potassium decreased with the increase of water content.(5)Under dry sifting treatment,with different treatments at different altitudes,with the decrease of agglomerate size,the content of soil air-drying aggregates showed a trend of increasing first and then decreasing gradually.After freeze-thaw treatment,soil aggregate structure and WMD and The GMD values decreased;under wet-sieve treatment,water-stable aggregates with particle sizes larger than 2 mm had the highest content at different altitudes,at 1-2 mm,0.5-1 mm,0.25-2.5 mm,and <0.1 mm.The content of particle size percentage was the second,and the content of water-stable aggregates with the size of 0.1-0.25 mm was the lowest.After freezing and thawing,the simulated freeze-thaw treatment soil aggregate structure,WMD and GMD values were decreased compared with the control at different altitudes.The freeze-thaw effect reduces soil stability and weakens erosion resistance.Overall,different soil after freezing and thawing treatment altitude,soil organic carbon are showed different degree is reduced,showed that freezing and thawing process each altitude simulation of freezing and thawing process of soil organic carbon is still able to relatively slow conversion process;And the soil available nutrients and easy oxidation of soluble substances such as carbon,ammonium nitrogen,effective phosphorus,phosphorus and potassium in addition to water treatment were showed increasing trend,to show the effectiveness of freezing and thawing is conducive to soil nutrient transformation,the high altitude area is of great significance to the nutrient requirement of plants growth,but at the same time,it shows that such as vegetation destruction will lead to increase the risk of nutrient loss,increase soil degradation;In addition,different freezing-thawing treatment results in soil non-water stability,water stability aggregates structure,WMD and GMD values all declined,indicating that freeze-thaw action will reduce soil stability.