| Farmland soil carbon pool is an important part of the global carbon pool and the core of soil quality.It is also the material basis for high and stable crop yields.Improving farmland soil organic carbon（SOC）sequestration is of great significance for sustainable agricultural development and mitigation of climate change.Although straw returning and farmyard manure are the main agronomic measures to maintain and improve the SOC level of farmland,the organic carbon turnover process such as the decomposition and mineralization of the native SOC and the formation of new SOC after the organic material enters the soil is also affected by soil nutrients,especially restriction and influence of the effectiveness of N.Therefore,exploring the response of the SOC sequestration process and mechanism to the organic material C entering the farmland soil,fertilizer N,and the interaction between the two has always been a hot issue in organic carbon research,and many aspects need to be in-depth explore.So far,although there have been many studies on microbial-dominated SOC turnover and regulation mechanisms,and most of them involve the stoichiometric ratio of microbial utilization of carbon and nitrogen,in terms of methods,most of them use short-term indoor culture experiment methods,and the results obtained are inconsistent with the actual field.In view of this,this study raises the following two scientific questions.One is the interaction between the net sequestration of SOC after the input of external organic materials and the availability of soil N and the input of exogenous N?Second,how do the input amount of organic materials and the amount of exogenous N affect the organic carbon turnover process and SOC retention?In order to answer the above questions,this study mainly adopts long-term positioning experiments with different N fertilizer dosages and different organic material management.From the 15 treatments in the two-factor experiment of fertilization method and nitrogen application rate,some of the treatments are selected according to the research purpose,and the soil is determined.Organic carbon,enzyme activity,yield and other indicators,by revealing the effects of different types and quantities of organic materials and nitrogen application on soil carbon retention and crop yield,and discussing their interaction mechanisms,in order to achieve high crop yields and high nutrient efficiency-environmentally friendly farmland management model based on field empirical research provides scientific basis.The main results obtained are as follows:（1）This experiment is based on a long-term positioning experiment（2002-2019）,with a control（CK）,Four treatments:returning straw（S）,applying nitrogen（N）,returning straw+applying nitrogen（S+N）;during the experiment period,the amount of N applied was 240kg hm-2,in the early period（2002-2016）and late period（2016-2019）Straw stalks are returned to the field by mulching and crushing in turn,and the amount of straw returned to the field is 4500 and 15000 kg hm-2 respectively.The results showed that the application of N（N,N+S）significantly increased wheat yield compared with non-N（CK,S）application,with an increase of 57.8%in the early stage and 68.3%,105%and 156%in the later stage,respectively.Prolonged,the effect of increasing production is more obvious;the effect of returning straw to production is significantly improved,up to 31.4%;compared with no N treatment,long-term application of N significantly increases the SOC storage and particulate organic carbon content（POC）in the 0-20 cm soil layer,easily oxidizable organic carbon content（EOC）and soil carbon management index（CMI）6.4%,13.3%,22.4%,27.0%;In 0-20 cm soil layer,straw returning significantly increase rates of the POC,DOC,EOC content and CMI were 48.3%,10.2%,49.2%and 58.7%respectively;the SOC storage,active organic carbon component and crop yield under the combination of straw returning and N application were higher.The results showed that the combination of straw returning and N fertilizer was beneficial to the sustainable development of grain production of wheat monoculture system and realized the win-win goals of SOC retention and yield increase.（2）This experiment uses a combination of 3 types of return to the field(0 kg hm-2without returning to the field,7500 kg hm-2 with a low amount of straw,and 15000 kg hm-2with a high amount of straw returning to the field)and a combination of 3 kinds of nitrogen application rates.When applying 120 kg N hm-2,compared with the non-returning of straw,the low-volume and high-volume return of straw both increased the SOC reserves by 14.2%and 17.1%,respectively.When the low-volume straw was returned to the field,the SOC sequestration was increased by 14.2%and 17.1%.MBC,DOC,and MBN all increased by20%,18.6%,and 5.7%,respectively.When the amount of straw returned to the field was high MBC,DOC,and MBN increased by 18.6%,45.9%,and 8.9%,respectively;The soil enzyme activity also increased with the amount of straw returning.It has a close positive correlation with SOC reserves and MBC.On the basis of 240 kg N hm-2,compared with non-returning,low-volume straw return and high-volume straw return have a significant effect on SOC sequestration and MBC,MBN and soil enzyme activity can improve,and the improvement effect is greater than that of moderate nitrogen application.Wheat grain yield increased with the increase of nitrogen application rate.Compared with N0,wheat grain yield of N120 and N240 both increased by 133.9%and 170.1%.It can be seen that both long-term nitrogen application and straw return are beneficial to soil carbon sequestration.When the two are used in combination with the highest amount,the carbon sequestration effect is the best,and the yield increasing effect is also the highest.（3）This experiment uses the combination of the above three different amounts of organic fertilizer(0 kg hm-2 without fertilization,30,000 kg hm-2 with low-volume organic fertilizer,and 45,000 kg hm-2 with high-volume organic fertilizer)and three types of nitrogen fertilizer,9 kinds of treatments.The results showed that with the increase in the amount of organic fertilizer,crop yield,nutrient content and absorption,SOC storage and its active components also showed an increasing trend.When under N120 conditions,compared with no organic fertilizer application,application of low amount of organic fertilizer increased SOC reserves by 23.8%,MBC 20.4%,DOC 13.5%,and soil enzyme activity also increased;Except for MBC,the effect of applying high amount of organic fertilizer on soil carbon index is far greater than applying low amount of organic fertilizer.Wheat grain yield increased with the increase of nitrogen application,the increase rate was37.3%and 42.4%,respectively;Regardless of high or low organic fertilizer application,there was no significant change in soil carbon index between N240 and N120,but MBC showed a downward trend.Which shows that after applying organic fertilizer,the increasing trend of high-volume nitrogen fertilizer on soil carbon retention is not obvious,and high-nitrogen dose will inhibit microbial activity and reduce the application of nitrogen fertilizer.To sum up:（1）The application of N fertilizer for 17 consecutive years only increases the SOC storage and active component content of the surface（0-20 cm）soil,especially when combined with straw returning is more conducive to SOC retention;N application can also significantly increase winter wheat The yield increases with the year of N application,and its yield increase effect is more obvious,indicating that the combination of straw returning to the field and N application is not only conducive to maintaining the level of soil fertility,but also conducive to stable increase in yield.（2）With the increase of straw returning,the enzyme activities related to the soil carbon and nitrogen cycle are improved,and then the SOC sequestration is promoted.The holding amount and enzyme activity also increase significantly with the increase of nitrogen fertilizer application,but the increase is less than that of straw returning.（3）SOC sequestration increased significantly with the increase of the amount of organic fertilizer and the amount of nitrogen applied;while the response of MBC to the availability of soil N was closely related to the amount of nitrogen applied,and high N would inhibit microbial activity.Therefore,the combined application of exogenous organic materials and appropriate amount of nitrogen fertilizer has certain application value in agricultural production. |
PDF Full Text Request