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Effects Of Different Biochar Control Modes On Physical Properties Of Freezing Thawing Soil

Posted on:2021-03-29Degree:MasterType:Thesis
Country:ChinaCandidate:H ZhaoFull Text:PDF
GTID:2370330602991022Subject:Agricultural Soil and Water Engineering
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The frequent occurrence of spring drought disasters in the alpine regions of the north,constrained by water resources and the effects of seasonal freeze-thaw in this area,the yield of crops in this area was greatly reduced,that is why the soil improvers were more popular for improving soil properties.Among them,the biochar has paid significant attention as an improver that changes the physical properties of soil.To date,there is limited point about soil improvement by biochar in seasonally frozen soil areas.In addition,it is not clear whether the effects of biochar application during different periods on soil physical properties are different.Therefore,it is incredibly important to explore the effects of applying biochar on soil structure and moisture characteristics in seasonal frozen soil regions in different periods to improve the high efficient use of agricultural water and soil resources and ensure food safety production.This paper is based on the Songnen Plain which is the China's main grain-producing area.On the basis of field experiments,three biochar applications were set up?Area A:application in the early stage of freezing,Area B:application in the middle period of thawing and Area C:addition of half of the biochar in the early stage of freezing and other half in the middle period of thawing?,including four biochar application rates(3,6,9 and 12 kgm-2).Explore the effects on soil structure,structural stability,and soil moisture characteristics separately.Finally,an efficient and reasonable application mode was explored to make it have the best improvement effect on soil physical properties.The main contents and conclusions are as follows:?1?Analysis of biochar addition on soil physical properties before and after freezing-thawing.Under the dual influence of seasonal freezing-thawing and biochar promoted the ratio of soil micro pore size??0.3-5?m?and soil voids?>100?m?;with the increase in carbon application,the proportion of extremely micro pore size?<0.3?m?decreased in different soil layers,and the soil total porosity?TP?of the soil increased significantly.The water-holding capacity of soil during the thawing period was higher than that during the freezing period,and compared with untreated soil,the water storage capacity was significantly enhanced.The soil hydraulic characteristic parameters were obviously changed before and after freezing-thawing.Although the higher carbon application led to increase in the plant available water content?PAWC?in different soil layers,it did not improve the soil water-air imbalance.The relative field capacity?RFC?suggested that excessive application of biochar might destroy the physical and chemical properties of soil.During the freeze-thaw period,it was found that when the amount of carbon is 6 kgm-2,the change range of soil liquid water content is the lowest.This improves the stable storage of soil moisture.Similarly,biochar increased the soil hydraulic conductivity of the same treatment before and after freezing and thawing,but with the increase of carbon application,the saturated hydraulic conductivity(Ksat)decreased gradually.?2?Analysis of biochar application during different periods on soil structure changes and structural stability.The choice and dosage of biochar application period had significant effect on soil structure,but there was no significant difference in the stability of the soil structure.Biochar significantly increased the soil TP and the content of aggregates with diameters>0.25 mm in the soil,and decreased the content of silt and clay fractions?S+C?in the soil.And the proportion of soil micro pore size?<0.3?m?was significantly reduced by all carbon treatments.Compared with control treatment,all 9 kgm-2 biochar treatments showed the best structural stability index.However,the high application of biochar resulted in too looser soil structure.From the applying period,it was found that area C had the best effect on soil structure improvement,which showed the application of biochar and experiencing freeze-thaw is a key factor in improving soil structure.Besides,the applying time and continuous application were helpful to the change and stability of soil structure.?3?Analysis of biochar application during different periods on soil swelling and shrinking modes Seasonal freezing and thawing can inhibit the vertical shrinkage of the soil.While the application of biochar inhibited the shrinkage effect of the soil in the vertical and horizontal directions at the same time before and after freezing and thawing,especially the amount of biochar was 9 kgm-2.However,it is found that the lower the amount of biochar applied in different periods,the more significant the inhibitory soil shrinkage effect,and the lower the amount of carbon applied also reduces the change range of soil bulk density before and after water loss and shrinkage.This is because biochar was affected by its structure while increasing soil pores,making it difficult to reduce its pores under external forces.On the contrary,freeze-thaw promoted soil swelling,while the application of biochar reduced the soil coefficient of linear expansion?COLE?.The main reason for the suppression was that the application of biochar improves the soil's large pore structure,thus alleviating the phenomenon of soil happen swelling.?4?Effects of biochar application during different periods on soil moisture characteristics.The application of biochar improved the soil structure,the water storage capacity in the soil pores was enhanced.At the same time,the storage effect of biochar's own pores indirectly improved the water retention of the soil.The optimum field capacity(FC=0.372 cm3cm-3)was obtained when the applied amount was 9 kgm-2.This was beneficial for the stable storage of soil moisture.The soil PAWC increased from 0.0638 cm3cm-3to 0.0927 cm3cm-3-0.1767 cm3cm-3,and this result was significantly related to the increases in soil TP and large aggregates?LA?.However,in the average liquid moisture content of the three application modes,none of the treatments in area B increased the liquid water content in the field soil.It was considered that only when biochar was applied in a reasonable period of time can maintained the stable supply of soil water.The effect of biochar application on soil pores results in the improvement of soil water conductivity.However,due to the small biochar particles blocking the soil pores,the low carbon treatments reduced the soil water conductivity.To sum up,it was believed that only reasonable application of biochar can have a positive effect on seasonal freezing thawing soil.It was found that the addition of half of the biochar content in the early stage of freezing and the other half in the middle period of thawing should be used as the most suitable carbon application period in seasonally frozen soil areas.Combined with seasonal freezing and thawing effect on soil moisture characteristics,it is recommended that the amount of biochar applied should be controlled between 6-9 kgm-2,which is beneficial to maintain the best soil structure and water characteristics.This study has a certain guiding significance for understanding the application of biochar in seasonally frozen soil areas and improving the sustainable development of agricultural water and soil resources and ecologies in cold regions.
Keywords/Search Tags:Biochar, Seasonal freezing and thawing, Different application periods, Soil structure, Soil moisture characteristics
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