Study On The Influence Mechanism Of Agricultural Measures On Soil Organic Carbon In Spring Corn Fields

Aimed at the decreasing trend of soil organic carbon content and the steadilydecreasing of soil fertility of spring maize farmland in the West Liaohe Plain of InnerMongolia, the studies on the farming technology system of carbon fixation and increasingproduction was urgently needed. In this dissertation, five farming measures includingfertilization, planting density, farming practices, subsoiling way and increased carbonfertility in high, middle and low-yielding fields were studied through three consecutiveyears field positioning experiment. Three analysis method including the carbon groupingmethod, organic carbon grouping method and three-dimensional fluorescence spectrometryanalysis method to determine dissolved organic matter were used, combined the qualitativeand quantitative analysis methods from enzymology and biology aspects, and thenanalyzed the content changes of soil carbon, organic carbon and organic carboncomponents in different farming measures, analyzed the dynamic characteristics of soilorganic carbon a in one spring maize growth period, revealed the influence mechanism ofthe soil enzyme activity and the spring corn growth on soil organic carbon, and clarifiedthe indicative significance of different organic carbon fractions to fertility and the effectof different agricultural measures on spring corn yield and soil organic carbon. Combinedwith regional characteristics and consolidated previous studies, the organic carboncomponent evaluation index system and model were established, and the suitable farmingmeasure system was confirmed in the region. The results were as follows:Fertilization was able to improve soil nutritional state, affected the dynamic balanceof soil carbon input and depletion. Fertilization made soil organic carbon content underfertilization increase from4.71%to34.84%. Compared with the application of organicfertilizer and inorganic fertilizer, the organic fertilizer made the soil carbon increased by6.24%to20.08%. Nitrogen fertilizer and organic fertilizer could significantly increase soilcarbon content. The fertilization mainly increased organic carbon content in the surfacelayer soil, and the increasing carbon effect decreased with the increase of soil depth.Phosphate fertilizer was able to improve the soil organic carbon content in corn’s earlyperiod, but to reduce the soil organic carbon content in corn’s late period. Nitrogenfertilizer was able to increase soil organic carbon content in corn growing period.Cooperation of organic and inorganic fertilizer had significantly increased soil organic carbon content.With the increasing of planting density, the carbon content was first increasing andthen decreasing, the organic carbon content was first decreasing and then increasing, andthe inorganic carbon content presented the upward trend in soil. Low density favored theaccumulation of organic carbon in the plow ground floor soil, and high density wasbeneficial for the accumulation organic carbon in the plow layer soil. High densityincreased the organic carbon content in surface soil in the early stage of corn growth, andincreased the topsoil organic carbon content in the late growth stages. Low densitypromoted the depletion of the plow organic carbon in the early stage of corn growth.Compared with traditional farming way, the different tillage systems made the soilorganic carbon content to increase from0.45%to3.73%. No-tillage was able to increasethe organic carbon content of spring corn in farmland soil. No-tillage subsoiling was ableto increase the organic carbon content of surface layer soil, and subsoiling was able toincrease the organic carbon content of plow soil. No-tillage subsoiling was the suitablefarming way for the spring corn high yield and increasing carbon in this region. Comparedwith conventional tillage, organic carbon in soil under different subsoiling methodsincreased from1.04%to7.21%. The soil carbon and organic carbon content wereincreased with subsoiling30cm. Compared with subsoiling40cm, the effect of increasingorganic carbon was significant by subsoiling30cm, and the effect in autumn was betterthan in spring and summer. The most suitable subsoiling way in this area was subsoiling30cm in autumn for the spring corn high yield and increasing carbon.The combined application of organic and inorganic fertilizer made the soil organiccarbon, active organic carbon, light fraction organic carbon, water-soluble organic carbonand microbial biomass carbon content increase by an average of0.16%,15.82%,48.83%,9.36%and9.32%in the high, middle and low-yielding field layers. It was also able tosignificantly increase the content of soil active organic carbon, mainly impacting thechanges in the composition of topsoil organic carbon. With the increasing of plantingdensity, active organic carbon in soil increased, and light fraction organic carbon reduced,and enhanced soil microbial biomass carbon under middle-density. The regression equationof the soil dissolved organic carbon contents and its yield was expressed as follow:(yield)=-4665.61-0.008×（SOC）-0.421×（ASOC）-0.777×（LFOC）+5.370×（DOC）+33.408×（MBC）. Active organic carbon and microbial biomass carbon were positivelyrelated to soil available phosphorus, potassium, nitrogen and corn production, whichimplies its indicative function to soil fertility. Fertilization was able to promote the humic acid and fulvic acid decomposition andtransformation in the surface layer soil. Fertilization encouraged soil organic mattercomposting degree in high and middle-yielding field, increased soil terrigenous dissolvedorganic matter in high-yielding field, and dissolved organic matter of biological source inmiddle and low-yielding fields. Fertilization made the fluorescence intensity of dissolvedorganic matter, dissolved organic carbon content, dissolved organic phosphorus contentand dissolved organic nitrogen content in the soil increase by an average of1.08%,9.36%,-3.39%and-7.54%, respectively. The regression equation of soil dissolved organic matterand its production was expressed as follow:(yield)=-2655.45+0.605×（DOM）-0.135×（DOC）+38.178×（DOP）-14.594×（DON）. Fluorescence peaks of soil humic acid andfulvic acid showed a significant positive correlation to soil dissolved organic carbon,dissolved organic nitrogen and dissolved organic phosphorus content, microbial carbon,nitrogen content and corn yield. Fluorescence intensity of soil dissolved organic matterreflected the soil fertility state, the stronger the fluorescence intensity was, the higher thesoil fertility was. Dissolved organic phosphorus is the main soil dissolved organic fractionsthat affect production in this region. Dissolved organic phosphorus content had theindicative function to soil fertility.Compared with inorganic fertilizer, the application of organic fertilizer was able toincrease the content of microbial biomass carbon, microbial biomass nitrogen by anaverage of44.55%,11.41%, and activities of sucrase, phosphatase and urease by anaverage of14.39%,12.29%and12.27%, respectively, and reduced catalase activity by37.7%. The application of nitrogen fertilization promoted urease activity. With the increaseof planting density, the soil sucrase activity had downward trend and phosphatase activityhad an upward trend. High planting density inhibited urease activity, and middle-densitywas beneficial for increasing the soil urease and catalase activity. No-tillage was able toincrease the content of microbial biomass carbon, microbial biomass nitrogen by anaverage of100.00%,11.35%, and promote soil sucrase, urease, phosphatase activities byan average of41.60%,47.02%and47.02%, respectively, and reduced catalase activity by10.34%. Subsoiling increased the content of microbial biomass carbon, microbial biomassnitrogen by an average of94.03%,7.30%, and increased soil invertase, urease andphosphatase activities by an average of37.29%,20.87%and21.87%, respectively, andreduced catalase activity by29.31%. Urease and phosphatase activities were relativelyhigh by summer subsoiling and catalase activity was relatively high by spring subsoiling.Invertase and catalase activity were higher by subsoiling40cm than that by subsoiling 30cm by an average of10.30%and50.40%, respectively, but urease and phosphataseactivities decreased by an average of8.93%and8.38%, respectively. Invertase, urease andphosphatase activities were positively related to soil organic carbon content and microbialcarbon content, while catalase activity was negatively correlated to soil organic carboncontent and microbial carbon content. The transformation among organic carbon, organicnitrogen and organic phosphorus affected each other in soil.Fertilization made the yield of spring corn increase by26.15%to52.66%. Organicfertilizer could significantly increase the corn kernel weight. The combined application ofphosphate fertilizer and organic fertilizer was beneficial for reducing the length of the bald.Too high density of the spring corn, increased of bald length and decreased of rows per earwas able to reduce single panicle; Single panicle under low density was improved byreducing the bald length and rows per ear, but rows per ear was too little and resulting inthe reduced yields, therefore the yield of middle density was the highest. Subsoiling wasable to improve the single panicle by increasing kernel weight and reducing the bald length,thereby increasing corn yields, no-tillage was able to increase corn production byincreasing kernel weight. Compared with the traditional farming way, subsoiling increasedthe yields of spring corn by3.59%. Autumn subsoiling was better than summer subsoiling,and summer subsoiling was better than spring subsoiling. Compared with subsoiling30cm,subsoiling40cm made the yields of spring corn increase by1.11%. Soil organic carboncontent had a significant positive correlation with kernel weight of spring corn, butnegative correlation with the bald length. Active organic carbon and microbial biomasscarbon had a significant positive correlation with yields and single panicle. The farmingtechnology for high yield and increased carbon of spring corn in this area was: combinedapplication of organic and inorganic fertilizer, medium-density, no-tillage subsoiling,autumn subsoiling40cm. The main indicator of soil fertility was active organic carbon.