Effects Of Different Organic Amendments And Mineral Nutrients Addition On Mineralization And Sequestration Of Soil Organic Carbon In Aeolian Sandy Soil

Fertile soil is a key component of plant growth and crop productivity.However,because many aspects of natural and artificial factors are involved in the evolution of soil fertility,which is quite complex;Moreover,if the agriculture management is improper,once the soil fertility is degraded,restoring and improving it will be extremely difficult.Soil organic carbon（SOC）is one of the important indicators of soil quality,which interacts with other processes and environmental factors such as soil properties,nutrient cycling,temperature and mineral nutrient.The input of organic materials such as manure,green manure,crop straw and biochar into the soil can improve the physical,chemical and microbial properties of the soil by increasing the SOC content,to improve the recoverability and sustainability of the crop-soil system.Although a large number of studies in China and other countries have shown that adopting organic fertilization measures to improve soil fertility is a viable option.For sandy soil with low fertility,how are the effects of different organic fertilization measures on SOC sequestration and their potential mechanisms different?Compared with straw and biochar from straw pyrolysis,can coal gasification waste slag and its converted biochar improve sandy soil fertility more effectively?At present,these problems still need to be explored in depth.The research in this area has important theoretical and production significance for improving the field fertility in the aeolian sandy soil area widely distributed in the arid areas of northern China.Taking the aeolian sandy soil in Mu Us sandy land of Shaanxi Province as the research object,this study carried out three independent indoor incubation experiments progress successively.By comparing the methods of adding organic materials such as crop straw,manure,coal gasification waste slag and pyrolysis biochar of different raw materials separately or in combination with mineral nutrients such as nitrogen,phosphorus and sulfur（to meet the stoichiometric ratio of microbial growth）,it aims to investigate the effects and possible mechanisms of these different organic fertilization measures on SOC mineralization and labile carbon fractions,microbial and soil enzyme activities,as well as soil chemical properties,so that we can provide the scientific and technical basis for improving soil fertility of aeolian sandy soil.The main results of the study are as follows:（1）The three factors studied in incubation I are straw addition,straw converted biochar addition and mineral nutrients addition,respectively.The eight treatments that form the complete design are control（CK）,mineral nutrients（Nu）,straw（S）,biochar（B）,mineral nutrients plus straw（Nu+S）,mineral nutrients plus biochar（Nu+B）,straw plus biochar（S+B）,the combination of mineral nutrients,straw and biochar amendments（Nu+S+B）.The purpose of this study is to reveal the effect of adding organic materials dominated by straw on SOC mineralization and sequestration in aeolian sandy soil.For the main effects of the factors,the results showed that the cumulative emission of CO₂ in soil added with straw was significantly increased by 359%,and the SOC content was significantly increased by 20%;however,the cumulative CO₂ emission of soil added with biochar decreased by 7-16%,while its SOC increased by 220%;the cumulative emission of CO₂ and SOC content of soil added with mineral nutrients increased significantly by 21%and 14%respectively.The addition of straw significantly increased the content of dissolved organic carbon and easily oxidized organic carbon in soil,with an increase of 65%and 93%respectively;the increase of biochar addition soil was 13%and 25%respectively,and the increase of nutrient addition soil was 21%and 21%respectively.Compared with CK,nutrients+straw treatment（Nu+S）significantly increased the average emission rate of soil CO₂ by 461%;Under the treatment of straw+biochar（S+B）,nutrients+straw+biochar（Nu+S+B）,SOC content increased by 167%and 207%respectively,compared with straw（S）treatment.The above results showed that the addition of biochar caused the negative priming effect of SOC mineralization in aeolian sandy soil,and its effect of improving SOC sequestration was much better than that of straw addition;the addition of nutrients with straw and straw biochar increased CO₂ emissions,but significantly increased SOC sequestration.（2）The three research factors of incubation II are wheat straw biochar addition,organic fertilizer addition and mineral nutrients addition.The complete scheme of eight treatments based on the addition of wheat straw is control（CK）,manure（M）,biochar（B）,biochar+manure（BM）,nutrient（N）,manure+nutrient（MN）,biochar+nutrient（BN）,biochar+manure+nutrient（BMN）.The purpose is to reveal the effect of adding other organic materials and nutrients on SOC mineralization and sequestration on the condition of adding degradable organic materials.The results showed that in terms of the main effect of factors,the addition of biochar did not significantly increase the cumulative CO₂ emissions but increased the particulate organic carbon（POC）and mineral-associated organic carbon（MAOC）by 127.25%and 105.92%respectively,and the SOC content and apparent carbon sequestration efficiency increased by 115.35%and 67.15%respectively.The addition of manure increased the cumulative emission of CO₂,the content of POC and MAOC,while the SOC content and apparent carbon sequestration efficiency increased by 42.42%and30.44%respectively.Nutrient addition increased CO₂ cumulative emissions and MAOC content by 52.37%and 11.30%respectively.Among the eight treatments,only adding biochar alone（B）significantly reduced the CO₂ emission rate,indicating that the combined addition of straw and biochar would cause a negative priming effect.Mantel test results showed that soil physical and chemical properties（p H,TN,AN）and hydrolase activity had a significant impact on microbial metabolism.Variation decomposition analysis showed that biochar addition accounted for 80.6%of SOC variation,which was the most important factor.The above results show that the combination of straw and biochar in aeolian sandy soil is more conducive to increasing SOC retention;the addition of straw,biochar,manure and NPS nutrients at the same time can significantly improve total nitrogen and microbial activity.Although it increases the cumulative emission of CO₂,it has better effects on improving SOC sequestration,stability and apparent carbon sequestration efficiency.It is an effective measure to quickly improve SOC sequestration in aeolian sandy soil.（3）The four research factors of incubation III are straw addition,straw biochar addition,coal gasification waste slag addition,and coal gasification waste slag biochar addition.On the condition of adding mineral nutrients,an incomplete（but partially complete）scheme is formed,including a total of 8 treatments:no addition of materials（CK）,nutrients（N）,straw+nutrients（S+N）,straw biochar+nutrients（SB+N）,coal gasification waste slag+nutrients（C+N）;Coal gasification waste slag biochar+nutrient（CB+N）,straw+straw biochar+nutrient（S+SB+N）,coal gasification waste slag+coal gasification waste slag biochar+nutrient（C+CB+N）.To explore the effect of coal gasification waste slag and its pyrolysis biochar application and the addition of straw and straw pyrolysis biochar on soil fertility improvement,the results showed that in terms of the main effect of the factors,the addition of maize straw,coal gasification waste slag and two kinds of biochar significantly increased the SOC content and microbial activity.The addition of straw biochar and coal gasification waste slag biochar significantly reduced the MBC content by 13%and 36%respectively.The p H value of soil added with coal gasification waste slag biochar was 15.48%higher than that of soil added with straw biochar.The cumulative emission of soil CO₂ added with coal gasification waste slag+biochar+nutrients（C+CB+N）is 8 times higher than that of CK.Under the condition of adding nutrients,the SOC content of straw biochar（SB+N）and straw+straw biochar（S+SB+N）increased by 97%and 37%respectively compared with that of straw only（S+N）;Similarly,the SOC of coal gasification waste slag biochar（CB+N）and coal gasification waste slag biochar+coal gasification waste slag biochar（C+CB+N）were significantly higher than that of soil with only coal gasification waste slag（C+N）,increased by 123%and 79%respectively.The above results show that under the condition of adding nutrients,whether straw biochar or coal gasification waste slag biochar if combined with relatively biodegradable organic materials,their SOC retention effect in aeolian sandy soil will be reduced.In summary,the addition of straw and coal gasification waste slag can only increase the mineralization loss of SOC,and when they are prepared into biochar and added to aeolian sand soil,they can significantly reduce the mineralization loss of SOC in aeolian sand soil.For aeolian sandy soil,only making straw into biochar can greatly improve the retention effect of SOC.Only by properly matching with mineral nutrients such as nitrogen,phosphorus and sulfur,can the SOC retention effect of various organic materials be further improved.On the condition of adding mineral nutrients,whether straw biochar or coal gasification waste slag biochar,if combined with relatively biodegradable organic materials,their SOC retention effect in aeolian sandy soil will be reduced.The addition of straw,straw biochar,manure and NPS nutrients at the same time increases the loss of SOC mineralization,but it has a better effect on improving SOC sequestration,stability and apparent carbon sequestration efficiency,which can be used as an effective measure to rapidly improve the SOC sequestration of aeolian sandy soil.