| The loss of organic carbon in cultivated land has been getting even worse with the increasing land utilization intensity.There is an urgent need to increase the organic carbon for the improving of soil structure and soil quality.In this thesis,three exogenous organic carbons,woody peat,herbaceous peat and brown coal,and potassium humate of woody peat(woody peat-HAK)were applied to the tobacco-planting soil,the effects of these exogenous organic carbons on the bulk density,moisture content,size distribution and stability of water-stable aggregates,labile organic carbon,carbon pool management index of tobacco-planting soil as well as the soil enzyme activities were investigated,their correlations were analyzed also.The main contents are as follows.1.Effects of three exogenous organic carbons on the size distribution and stability of water-stable aggregates,labile organic carbon contents and enzyme activities of tobacco-planting soil were investigated.The mean mass diameter(MWD)and geometric mean diameter(GMD)of water-stable aggregates in the tobacco-planting soil increased 23%,13%,21% and 33%,18%,31%,respectively,twelve months after the application of 2%woody peat,2% herbaceous peat and 2% brown coal.In addition,the labile organic carbon(LOC),high labile organic carbon(HLOC)and carbon pool management index(CMI)of tobacco-planting soil increased significantly,and the increasing amplitude follows the order of woody peat > herbaceous peat > brown coal.Almost all of the soil bulk density,moisture content and soil catalase activity unchanged after the three exogenous organic carbon treatments.The soil invertase activity decreased 54.6% and soil urease activity increased25.9% twelve months after the application of 2% woody peat,while no significant changes in soil invertase activity and soil urease activity were seen during the treatments of 2%herbaceous peat and 2% brown coal.2.The effects of the application dosage of woody peat on the water-stable aggregates,labile organic carbon contents and enzyme activities of tobacco-planting soil were investigated.The proportions of soil water-stable aggregates with diameter greater than 2mm(WR>2),especial those larger than 5 mm(WR>5),as well as the LOC,HLOC and CMIincreased with the application dosage of woody peat.The MWD and GMD of tobacco-planting soil increased from 15% to 43% and from 21% to 79%,respectively,while the LOC,HLOC and CMI increased from 51% to 214%,from 55% to 318% and from 55%to 239%,respectively,twelve months after the woody peat use of 1% to 4%.However,the soil invertase activity decreased with the increase dosage of woody peat,from 54.6% to63.4%.In addition,the soil urease activity increased from 5.7% to 25.9%,but no significant change of soil catalase activity was observed after the application of 1% to 4% woody peat.The soil bulk density increased and the soil moisture content decreased when the application of woody peat more than 3%.3.The proportions of soil water-stable aggregate with diameter greater than 2 mm,especial those larger than 5 mm,as well as the LOC,HLOC,CMI and soil catalase activity increased with the application dosage of woody peat-HAK.The MWD and GMD of tobacco-planting soil increased from17% to 120% and from 22% to 201%,respectively,while the LOC,HLOC,CMI and soil catalase activity increased from 37% to 751%,from60% to 545%,from 38% to 951% and from 0.9% to 15.5%,respectively,six months after the woody peat-HAK application of 1% to 7%.However,the invertase activity and urease activity of the tobacco-planting soil increased significantly after the woody peat-HAK treatments of 1% to 7%.The maximum increased amplitude of 281% and 169% was observed in the case of 4% woody peat-HAK treatment.In addition,the soil bulk density decreased from 1.97% to 5.92%,while soil moisture content increased from 11.0% to 29.0%,respectively,with the application dosage of woody peat-HAK increased from 2% to 7%.4.The MWD and GMD of tobacco-planting soil increased with the increase dosage of woody peat application from 59% to 500% and from 51% to 853%,respectively,twelve months after the woody peat application from 5% to 15% under tobacco planting.However,all of the soil water-stable aggregate proportions larger than 0.25 mm(WR> 0.25),increased after the 5% and 10% of woody peat treatment,while only the WR>5increased for the 15%of woody peat treatment.The LOC and HLOC were not kept increasing after the 10%woody peat treatment,with the maximum LOC and HLOC of 2197% and 469%,respectively;The soil invertase activity and soil urease activity decreased 36.7% and 20.5%,respectively,twelve months after 5% woody peat application under tobacco planting,while for the 10% and 15% woody peat treatments,the soil invertase activity increased 17.3% and92.0%,and the soil urease activity decreased 43.8% and 38.8%,respectively.No significant change was observed in the three treatments.The soil bulk density decreased from 6.3% to16.0% with the application dosage of woody peat increased from 5% to15%,while the increase of soil moisture content is not affected by the application dosage of woody peat.5.The labile organic carbon content and carbon pool management index were positive related to the soil water-stable aggregate proportions,MWD and GMD significantly,while there were no significant correlation between the soil enzyme activities and soil water-stable aggregates. |
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