Characteristics Of Nitrogen Release And Adsorption Dinamics By Rape And Rice Straw Incorporation

The release of nutrients,the holding of nutrients by straw itself and the effect of straw returning on soil nutrient transformation during straw returning play an important role in improving the effectiveness of soil nutrients.In this study,field experiments and indoor simulation experiments were combined to study the following three aspects:?i?field trials were conducted to study the characteristics of rice straw decomposition and nutrients release during the whole growth period of rape;?ii?soil from long-term fertilization experiment was collected for an indoor culture experiment to analyze the effect of adding different C/N ratios straw on the mineral nitrogen?N?content under long-term straw returning;and?iii?rice and rape straw were used to simulate the ammonium?NH₄⁺?adsorption characters and the impact factors.The research results would provide the theoretical basis for the reasonable management of straw nitrogen return.The main findings are as follows:1.The straw mulching experiment during the rapeseed growth season showed that the average decomposition rate of rice straw during the 157-228d was three times of the initial release period?0-157d?.Precipitation and>0°C accumulated temperature are the key factors that constraining the decomposition of the early straw.The late rainfall?a sudden increase at 150 days?and the accumulated temperature of>0°C?a significant increase at 180 days?promote rapid decomposition.The cumulative nutrients release rate of straw were presented as K>N>P.The K release of straw was the most obvious,but the nitrogen and phosphorus content of straw did not change significantly.There was a negative value of N and P release rates in the early stage of straw decomposition,indicating that N and P were adsorbed in the early stage of straw decomposition.2.The results of soil indoor experiments adding different C/N straws showed that the contents of ammonium N,nitrate N and mineral N in soils treated with urea and straw were significantly increased.The overall performance was as follows:Urea>Straw C/N24>Straw C/N36>Straw C/N55>Control.In the non-sterile treatment,the ammonium nitrogen in the soil significantly decreased on the 50th day.At the end of the culture?day 130?,the nitrate N and mineral N content of long-term straw returning soil?NPKS?were significantly higher than NPK.In the non-sterilized condition,the increase in mineral N content in the NPKS treatment group were 2.57%to 9.93%higher than that in the NPK treatment.In the NPKS treatment group,the increase in mineral N treatment was 15.76%to 34.44%higher as compared with the NPK treatment.3.The results of ammonium N adsorption test show that increasing the initial concentration of the solution,appropriately increasing the ambient temperature,the solution in a neutral or alkaline environment,increasing the adsorption time and contact area,were all conducive to increasing the amount of straw adsorption.The recommended conditions for the straw to adsorb ammonium nitrogen were:0.25 g straw,25⁴0°C temperature,higher initial concentration,pH between 7⁹,adsorption time 4h,complete contact state.4.By SEM and FTIR analysis,rice straw had more mastoid than oilseed rape straw,and its specific surface area was larger,and its pores were more obvious.The vibrational form of functional groups appeared after the straw adsorbed ammonium nitrogen,producing a new structure.Adsorption included both physical and chemical adsorption.The results of adsorption kinetics at different concentrations showed that the equilibrium adsorption capacities of 4 mg/L,12 mg/L,and 20 mg/L rapeseed straw were 0.33 mg/g,0.61 mg/g,and 0.79 mg/g,respectively,and the equilibrium adsorption capacity of rice straw.It was 0.39 mg/g,1.29 mg/g,2.49 mg/g in that order.The kinetic characteristics of the adsorption of ammonium nitrogen by oilseed rape and rice straw were described using four equations:quasi-first order,quasi-second order,elovich and intragranular diffusion.It was found that the pseudo first-order kinetic model R2 was higher and more consistent with the actual adsorption capacity.So a quasi-first-order kinetic model is the best model.4.In the static adsorption thermodynamics test of straw,the adsorption isotherms at different temperatures indicated that the adsorption capacity of 278 K,298 K and313 K rapeseed straw was 0.11 mg/g,0.20 mg/g,and 0.25 mg/g,respectively.The equilibrium adsorption capacity of straw was 0.23 mg/g,0.26 mg/g,and 0.32 mg/g,respectively.The Langmuir adsorption isotherm equation can better describe the regularity of ammonium adsorption at different temperatures of rice straw?R2:0.95⁰.97?and rape straw?R2:0.69⁰.90?.The Langmuir and Freundlich adsorption isothermal model effects of rice straw Better than the simulation effect of rape straw.The calculation results of adsorption thermodynamic equations show that the isotherm adsorption process of ammonium adsorption by straws with enthalpy change??H?>0,entropy change??S?>0,free energy??G?<0,is an increase in endothermic entropy.The adsorption method is mainly based on physical adsorption.5.The results of straw dynamic adsorption test show that increasing the concentration of the initial solution of ammonium nitrogen or increasing the flow rate of the system solution can shorten the time for the straw to reach equilibrium and increase the amount of straw adsorption.Under the same conditions,rice straw has stronger adsorption capacity for ammonium nitrogen than rape straw.In this experiment,the recommended flow rate was 5 ml/min and the ammonium nitrogen concentration was 16 mg/L.At this time,the adsorption rates of ammonium nitrogen by rapeseed and rice straw were 57.3%and 88.6%,respectively.