Effects Of Adding Organic Matter To Farmland On Soil Characteristics And Rhizosphere Process Of Efficient Utilization Of Nitrogen In Cotton In Arid Areas

Soil organic carbon and total nitrogen in arid areas have been always at a low level.Stalk residue retention as one of the important measures to increase carbon and nitrogen input which has been attracted researches extensive attention.With the adjustment of the agricultural industrial structure and the rapid development of animal husbandry,animal manure has been widely used by cotton farmers as an organic fertilizer.Animal manure and straw residue retention are relatively abundant fertilizer resources in arid regions,and the application of organic manure and residue retention have gradually been becoming the main way to improve the yield and economic benefit of cotton.Aiming at the problems of large amount of nitrogen fertilizer input and low fertilizer utilization rate under drip irrigation,one field experiment was conducted which use a split-plot design included two main plot treatments(stalk residue removal and stalk residue retention)and four subplot fertilizer treatments(no fertilizer,nitrogen(N),phosphorus(P),and potassium(K)fertilizer,poultry manure,and NPK plus poultry manure).In this paper,we discussed the effects of nitrogen fertilizer input amount and agricultural management measures on soil N conversion and soil characteristics in cotton fields in the arid area,as well as cotton rhizosphere processes,N uptake,and changes in organic carbon pools under high-efficiency nitrogen utilization.The main results of this research are listed as below:1.The results showed that stalk residue retention increased soil pH whereas fertilization reduced it.Stalk residue retention and fertilizer application both increased organic carbon,total nitrogen,and microbial biomass carbon.The NPK plus poultry manure treatment had the highest nitrate and available nitrogen contents.Stalk residue retention plus fertilization had positive rhizospheric effect on soil organic carbon and nitrate nitrogen,negative rhizospheric effect on total nitrogen and ammonium nitrogen,and no net rhizospheric effect on soil pH and microbial biomass carbon.Stalk residue retention improved soil quality and increased soil organic carbon and available nitrogen.Stalk residue retention plus NPK fertilizer and poultry manure can significantly increase soil organic carbon and active carbon components,thus ensuring high productivity.2.The results showed that stalk residue retention can increase soil net mineralization,net nitrifation,gross nitrication,denitrification,nitrate nitrogen,ammonium nitrogen and absorbable inorganic nitrogen content.The NPK plus poultry manure has the largest soil net mineralization,net nitrifation,gross nitrication,denitrification,nitrate nitrogen and absorbable inorganic nitrogen content.Application of stalk residue retention combined application of NPK fertilizer and chicken manure were been helpful to accelerate the transformation of soil nutrient,improve efficiency of fertilizer and then increase the effective content of nutrient in arid areas.3.The results showed that with the measures of stalk residue retention,the NPK plus poultry manure has the largest urease and invertase activity.Stalk residue retention,chemicalfertilizer mixed manure significantly improved the utilization ability of carbon source meanwhile increased the diversity of microorganism after comparing the comprehensive work of different management.The capability of using different carbon sources of microorganism was variant,carbohydrates,amino acids and polymers were mainly utilized under the treatment of chemical fertilizer plus organic fertilizer followed by the treatment of chemical fertilizer.4.The results showed that stalk residue retention had no effect on root mean diameter,root tissue mass density,specific root length,or root specific surface area.Fertilization increased root tissue mass density and root specific surface area while decreased specific root length,while root mean diameter was not affected by fertilization treatment.Stalk residue retention had no significant effect on root vigor and glutamine synthetase,and fertilization increased root vigor and root glutamine synthetase activity.Stalk residue retention and fertilization increased soil available nitrogen,available phosphorus,and available potassium.Moreover,the effective nitrogen use,effective phosphorous use,and effective potassium use in roots were found to be sensitive to fertilization measures,and stalk residue retention was found to have a significant effect on the effective nitrogen,effective phosphorous use,and effective potassium use of total dry matter.Stalk residue retention significantly reduced the root-shoot ratio of cotton and had no significant effect on root biomass and fine/coarse root mass ratio.Fertilization significantly increased the root-shoot ratio,root biomass,fine/coarse root mass ratio,and seed cotton yield.Overall,the combination of NPK fertilizer and poultry manure significantly affected the root morphology and achieved the largest root physiological activity and soil nutrient content.The addition of poultry manure or stalk residue retention was found to promote root growth,enhance the activity of nitrogen absorption enzymes,delay root senescence,and ultimately increase crop yield.5.The long-term(10 years)changes in soil carbon storage capacity,source-sink relationship,and yield effects of cotton fields under different fertilization and stalk residue retention treatments were studied.The results show that the soil organic carbon content in the treatment of combination of NPK fertilizer and poultry manure is significantly higher than fertilizer application,with an annual increase rate of 30.3%.The combined application of NPK fertilizer and poultry manure can effectively reduce the soil bulk density and maintain the soil structure,while the application of straw can only improve the soil fertility of the plow layer.The organic carbon storage under organic fertilizer treatment was significantly higher than that in NPK fertilizer treatment,and the organic fertilizer treatment was 11.5% to 15.1%higher than no ferilizer.Soil carbon sequestration efficiency does not remain the same as the carbon input increases.In the eighth year,the carbon sequestration efficiency slightly decreased.After 10 years of fertilization and stalk residue retention treatments,the seed cottonyield showed a significant upward trend.Soil organic carbon content also has significant correlation with seed cotton yield.With the increase of carbon input,the yield increases.Therefore,the combined application of NPK fertilizer and poultry manure has asignificant effect on the improvement of soil organic carbon content,organic carbon density,and carbon fixation rate.The application of organic fertilizers will reduce the dependence of crops on soil fertility and promote high and stable crop yields.