Study On Soil Carbon Distribution,Leaching And Straw Rot Interpretation Carbon In Cotton Area Of The Upper Reaches Of Tarim River

Farmland soil carbon pool plays an important role in the terrestrial carbon cycle,and the change of soil carbon content is of great significance to soil carbon pool.As the main carbon storage sites in arid areas,the mineralization,sequestration,leaching and plant uptake of carbon elements in ecosystems are closely related to agricultural production practices.Alar Reclamation area is located in the north of Tarim Basin,where the problems of extreme drought,salinization and barren soil are very prominent.At present,large-scale land development and utilization has changed the physical and chemical environment of soil,which has seriously affected the balance of soil carbon pool.Fertilization and irrigation are important measures to maintain soil productivity and improve crop yield in the study area,which have a profound impact on soil carbon decomposition and conversion.Therefore,in this study,the spatial distribution and profile carbon storage characteristics of soil carbon in the upper reaches of the Tarim River were analyzed on a regional scale,and the leaching,migration and accumulation of carbon in the cotton field in the upper reaches of the Tarim River under different irrigation and fertilization modes were studied through the undisturbed soil column test and the indoor simulation experiment of cotton straw returning to the field under different conditions.It provides theoretical basis for improving the water input of cotton field in southern Xinjiang,scientific and reasonable fertilization,reducing the leaching of soil carbon,improving the capacity of soil carbon sequestration,and protecting the sustainable development of ecology.The main research results are as follows:（1）The soil organic carbon in 0～200 cm soil layer in cotton area of the upper reaches of Tarim River mainly accumulated in 0～100 cm soil layer and decreased with increasing depth.The average content of soil organic carbon in 0～20 cm surface soil was 5.74 g·kg^-1.The minimum value of 1.47 g·kg^-1appeared in the bottom180～200 cm,accounting for only 25.61%of the surface content.The organic carbon in 0～100 cm soil accounted for 67.30%of the organic carbon in 0～200 cm soil.Inorganic carbon was mainly accumulated in the 100～200 cm soil layer,showing a trend of"low-high-low-high"on the whole.The content of inorganic carbon in the80～100 cm soil layer was the highest 23.59 g·kg^-1,and the maximum increase was34%in the 60～80 cm soil layer.The inorganic carbon storage of 100～200 cm soil accounted for 54.48%of that of 0～200 cm soil.The variation coefficient of organic carbon and inorganic carbon in the study area ranges from 22%to 60%,which belongs to moderate intensity variation.（2）The undisturbed soil column test showed that both the amount of water and nitrogen input and the input mode affected the content of organic carbon and inorganic carbon and the leaching amount in soil.When nitrogen application rate increased from 270 kg·hm^-2to 450 kg·hm^-2,the leaching loss of soluble organic carbon and soluble inorganic carbon was significantly increased.When water input increased from 6000 m³hm^-2to 9000 m³hm^-2,the leaching loss of DOC and DIC was the highest,and the leaching loss of carbon under drip irrigation was higher than that under flood irrigation.The results showed that water and nitrogen input and irrigation method were the factors affecting soil carbon leaching.Under the condition of excessive water input,long-term high frequency irrigation was the main factor affecting soil carbon leaching.The amount of water and nitrogen input and the way of water input jointly affected soil carbon content and had a strong interaction effect.Under the same treatment,organic carbon content decreased gradually with the increase of soil layer.The organic carbon content in 0～20 cm soil layer was the highest under diffuse irrigation and medium nitrogen(360 kg·hm^-2)treatment,the organic carbon content in 20～40 cm soil layer was higher under drip irrigation and low nitrogen(270 kg·hm^-2)treatment,and the organic carbon content in 40～60 cm soil layer was higher under drip irrigation and medium nitrogen(360 kg·hm^-2)treatment.There was no significant change in inorganic carbon content in 0-60 cm soil layer.Drip irrigation and low nitrogen(270 kg·hm^-2)treatment had a higher inorganic carbon content in 0～20 cm soil layer,while flood irrigation and medium nitrogen(360 kg·hm^-2)treatment had a higher inorganic carbon content in 20～40 cm soil layer.The inorganic carbon content was higher under drip irrigation in 40～60 cm soil layer and medium nitrogen(360 kg·hm^-2)treatment.（3）The results of straw decomposition test showed that with the prolonging of decomposition time under each treatment,the decomposition rate of straw increased and the residual amount decreased.The change of chemical composition of cotton stalk was mainly manifested in the decomposition of cellulose and soluble sugar in cotton stalk,but there was no significant difference among different treatments.However,the decomposition of lignin was very slow,which limited the decomposition of cotton straw.The lower the temperature,the higher the salt content and the higher the water content,the more difficult the decomposition of cotton straw lignin.At 25℃,60%field water capacity and 0.3%soil salt content,the decomposition rate of straw was the highest,and the release rate of organic components was the fastest.Suitable temperature,moisture and salt content can increase the soil organic carbon content,especially the surface soil（0～20 cm）.Among them,25℃,60%field water capacity and 0.3%soil salt content treatment had the largest increase of soil organic carbon,and the largest increase of organic carbon storage.