Effects Of Slope Gradient And Position On Organic Carbon And Nitrogen Fractions And Aggregate Composition In Tobacco-growing Soil

Soil carbon and nitrogen are important indicators for measuring soil quality.Soil carbon and nitrogen dynamic balance in tobacco area will directly affect soil fertility level and tobacco leaf quality.Aggregate as a material basis for soil fertility also has a profound impact on organic carbon and nitrogen.As the main producing area of Sichuan flue-cured tobacco,Liangshan tobacco area is concentrated in the high-altitude sloping farmland.The distribution of the flue field along the mountain and the slope of the slope are large,which will affect the balance of soil carbon and nitrogen and the composition of agglomerates.The soil fertility level of tobacco planting has a significant impact.This paper takes the typical tobacco-growing area of Liangshan Prefecture as the research object,which is divided into different slopes(<5°,5-10°,10-15°,15-20°)and slope position(uphill slope,mid-slope slope).A total of 81 soil samples(0-20cm)and lower layer(20-40cm)were collected from the slopes and downhill slopes.The total organic carbon,soluble organic carbon and easily oxidized organic carbon were analyzed.Soil carbon and nitrogen morphological indexes and soil aggregate composition of total nitrogen,soluble nitrogen,ammonium nitrogen and nitrate nitrogen were studied.The effects of slope position conditions on soil organic carbon and nitrogen forms,soil aggregate composition and stability were studied.The research results are as follows:(1)As the slope increases,the soil organic carbon content gradually decreases,compared with the I grade slope(0-5°),II(5-10°),III(10-15°),IV(15-20°).The total organic carbon content of the soil decreased by 18.43%,23.09%,and 37.24%,respectively.The sloped area(0-5°),the moderate slope area(5-15°)and the steep slope area(15)-20°)The difference in soil organic carbon content reached a significant level.Particulate organic carbon and inactive organic carbon also show a gentle slope(0-5°)> medium slope(5-15°)> steep slope(15-20°),the difference is significant.Soil carbon pool activity(A),soil carbon pool activity index(AI)and carbon pool management index(CPMI)and DOC/TOC(soluble organic carbon/total organic carbon),ROC/TOC(easy to oxidize organic carbon/total Organic carbon)has increased as the slope increases,and the carbon pool management index(CPI)decreases as the slope increases.The total organic carbon and the content of organic carbon in the soil were the highest in the mid-slope soil,but the soil carbon pool activity(A),soil carbon pool activity index(AI)and carbon pool management index(CPMI)were the lowest.In general,the lower the soil organic carbon content,the higher the carbon storage activity and the worse the carbon storage stability.According to the effect of slope and slope position,under the condition of grade I slope,the slope of the soil carbon pool is not significant under the slope of grade II,III and IV.(2)The slope change has a significant effect on soil nitrogen and its components.With the increase of slope,the nitrogen content of each form gradually decreases,and the ratio of soil nitrogen to total nitrogen also decreases.The greater the slope The effectiveness of the soil nitrogen pool is reduced,and the rate of loss of available nitrogen with increasing slope is also increasing.Nitrogen and organic carbon showed a consistent trend in different slope positions,and the highest content was found in the mid-slope.However,the ratio of nitrogen to total nitrogen was the highest,and the nitrogen pool activity was lower.Higher.The effects of comprehensive slope and slope position on nitrogen,soil total nitrogen,soluble total nitrogen and nitrate nitrogen content in the upper and middle slope soils showed a decreasing law with the increase of slope,soluble total nitrogen,The ammonium nitrogen and nitrate nitrogen showed different trends with the change of total nitrogen in different slope soils under different slope conditions.The slope of the study area is the main factor regulating the nitrogen distribution on the slope.(3)The slope position change has obvious influence on the agglomerates.The percentage of non-water stable aggregates >2mm shows a decrease with the increase of slope,but the percentage increases with the decrease of slope position.The percentage of large agglomerates >2 mm in water-stable agglomerates also increases with increasing soil slope.The slope of the soil increased R0.25 and the average weight diameter showed a downward trend,and the soil structure became more unstable.However,as the slope decreased,the soil R0.25 and the average weight increased,and the soil was in the downhill and mid-slope positions.Soil aggregates have a better structure.The agglomerate structure failure rate(RSD)increases with the increase of slope.The greater the slope,the more unstable the soil structure.The agglomerate of the mid-slope is smaller than the up-slope and down-slope,and its agglomerate has the best stability.Soil organic carbon total nitrogen is mainly present in large aggregates >2mm,and particulate organic carbon and soluble total nitrogen are more related to large aggregates,and mineral nitrogen is more present in aggregates <1mm.In summary,the sloped slope soil in the study area has higher organic carbon and nitrogen,which is more effective than the upper and lower slopes of the straight slope,and the soil is more effective.The more carbon and nitrogen are lost,the worse the stability of soil aggregates.Soil total organic carbon and total nitrogen are mainly related to medium and large particle size aggregates,and soluble nitrogen is more present in small particle size aggregates.Therefore,more attention should be paid to the effect of slope change on soil carbon and nitrogen changes.Relevant prevention measures.