Changes Of Soil Carbon And Nitrogen Components And Their Coupling Characteristics In Peach Orchard At Different Slope Positions Under The Cover Of Light Leaf Blade

Longquanyi District is the "hometown of peach in China".The peach industry is an important support for the development of agricultural economy in Longquanyi District,and the quality and health of peach garden soil is an important guarantee for the development of peach industry.According to the nutrient classification standard of the second national soil survey,the contents of organic matter and alkali-hydrolyzed nitrogen in the topsoil in Longquanyi area are mostly concentrated at grade 4 level,which is relatively lacking;total nitrogen content is medium high level;available phosphorus content is mostly at grade 2and 3,which is medium low level;available potassium content is mostly concentrated at grade 3,which is medium low level.It is necessary to explore a good treatment mode to improve the soil.In this study,the peach garden of Baishi Village,Longquanyi District,Chengdu City,Sichuan Province,was selected for field experiment.The test area was divided into upper,middle and lower slopes according to the distance from the top of the slope.Each slope was covered by light leaf purple flower with the cover treatment for three years,and the clear tillage was taken as the control.Physical and chemical indexes such as soil total carbon,total nitrogen,granular organic carbon and nitrogen,easily oxidized organic carbon,alkaline hydrolyzed nitrogen,nitrate nitrogen and ammonium nitrogen were measured at different growth stages and depths,and the change characteristics of carbon and nitrogen components were compared and analyzed,as well as the coupling relationship between carbon and nitrogen was analyzed,so as to provide scientific basis for soil improvement in peach orchard and explore the improvement effect of grass mulching on peach orchard soil.Explore a more efficient and convenient grass growing mode.The main results are as follows:(1)The contents of soil total organic carbon,easily oxidized organic carbon,dissolved organic carbon,granular organic carbon,alkali-hydrolyzed nitrogen,dissolved total nitrogen,granular organic nitrogen,ammonium nitrogen,nitrate nitrogen,available phosphorus and available potassium were significantly increased by grass mulching at different slope positions.There was no significant difference between the total nitrogen content of grass mulching treatment and clear tillage treatment,but the overall total nitrogen content of grass mulching treatment was generally higher than that of clear tillage treatment.At the same time,grass mulching also significantly improved the water content and porosity of each slope position,and reduced the bulk density.With the change of growth period,the changes of all available carbon and nitrogen components showed a trend of first increasing and then decreasing,especially in peach fruit maturity stage.The results showed that dissolved organic carbon,total nitrogen,available phosphorus and available potassium were slightly higher at flowering stage than at fruit maturity stage,and the results were the lowest at dormant stage.There was no significant change in physical properties with growth stage.The increase of carbon and nitrogen components and the improvement of physical properties of grass mulching treatment showed a gradual decline with the deepening of soil layer.(2)The content of carbon and nitrogen components,water content and porosity of different slope sites showed that the lower slope was significantly higher than that of the upper slope,and the bulk density of the lower slope was significantly lower than that of the upper slope.The difference of nutrient content and physical indexes between the middle slope and the upper and lower slope sites had different responses in different growth periods and soil depth.In each growth period of peach trees,the nutrient content of each slope position as a whole showed that the flowering stage and fruit maturity stage were close to each other,and the resting stage was the lowest.Among different soil layers,with the deepening of soil layer,the improvement of soil nutrients and physical indexes of each slope position had a gradually decreasing trend.(3)Compared with clear tillage,grass mulching significantly increased soil carbon pool index and organic carbon storage,indicating that grass mulching could improve soil carbon pool activity without reducing the stability of soil carbon pool.There was a significant positive correlation between most carbon and nitrogen components in soil.In this study area,organic carbon content was deficient,total nitrogen content was at the national average level,and C/N remained between 4 and 7.With low ratio,grass mulching was beneficial to improve soil C/N.Through principal component analysis of 15 indexes,including total organic carbon,easily oxidized organic carbon and dissolved organic carbon,the results showed that the soil fertility score of grass mulching was the highest in the topsoil of downhill position at fruit maturity stage,and grass mulching treatment was significantly higher than that of clear tillage control.The soil fertility score had a tendency to decrease gradually.