Distribution Of Tropical SOC And Its Relativity Study Under Land Utilization Patterns

Soil is one of the largest and most active carbon pools in the Earth's surface system,soil organic carbon?SOC?is an important component of soil carbon pools.It is estimated that the global SOC reserves are about 1550Pg(1Pg=10¹⁵g).It is three times as large as the atmospheric carbon pool and 2-4 times that of the terrestrial vegetation carbon pool.Therefore,the soil carbon pool small changes will cause fluctuations of CO2 concentration in the atmospheric,which in turn has a major significant on the global climate.In addition,SOC has an important impact on soil quality,fertility and sustainable productivity of soil SOC not only provides carbon source for vegetation growth,but also has significant influence on soil physical,chemical,thermal characteristics and soil biological activity,and the content increasing of SOC can improve soil micro-aggregate structure and improve soil structural stability and corrosion resistance.Enhancing soil water retention and fertilizer retention,it is plays a key role in maintaining soil quality and maintaining stable yield.Therefore,SOC research has become one of the most popular concerns.Studies have shown that land-use patterns can affect the accumulation and release of SOC,structure and decomposition rate,and have a profound impact on the carbon cycle in the Earth's surface system.Therefore,it is great significance to study the distribution of SOC under different land-use patterns and its correlation with soil physical and chemical properties to improve soil carbon sequestration,soil sustainable use and agricultural production activities.However,although many studies have been done on soil organic carbon,but it's mainly focus on the estimation of soil organic carbon content and the spatial distribution characteristics and its influencing factors,but what is the difference of the impact degree and influencing factors under different land-use patterns?How is it?Many problems have not been solved such as the degree of soil carbon sequestration and soil physical and chemical properties under different land-use patterns,even some problems have different conclusions.As far as Hainan is concerned,its location in the tropics,the land utilization rate is much higher than that in other parts of the country,the human activities are frequent disturb,and the land-use pattern has a greater impact on the accumulation of SOC.However,there are relatively few studies on the distribution of SOC,its influence mechanism and its relationship with soil physical and chemical properties under different land-use pattern in the region,there is no clear conclusion about the effect of different land-use on organic carbon accumulation.Therefore,it is of great theoretical and practical significance to explore the distribution characteristics of soil organic carbon in the area and to understand its relationship with soil properties to improve soil quality and achieve sustainable use of soil resources.In this study,9 representative administrative villages were selected as the main sampling areas,the farmland,vegetable plots,abandoned land and economic forest land were selected as research objects.Through data collection,field sampling and laboratory treatment analysis,analysis the distribution characteristics of SOC and particulate organic carbon?POC?,mineral organic carbon?MOC?and aggregate organic carbon under land-use pattern,and clarify the relationship between physical with SOC,to provide reference for regional soil quality improvement and sustainable use of soil quality.The main conclusions of the study are as follows:?1?The content of SOC in the study area was 0.37?21.19 g/kg,the average value was8.70±1.48 g/kg,and the coefficient of variation was 0.67,which indicated the distribution of TOC in the study area had spatial variation.There were differences in SOC content under different land-use patterns,which were paddy farmland>less than 3 years of abandoned land>vegetable land>3?8 years of abandoned land>8?10 years of abandoned land>economic forest land.In the vertical direction,it showed a trend,that is,with the increase of soil layer,the SOC content decreased,and the highest SOC content appears in the surface layer,which indicated that the SOC in the study area had“aggregation phenomenon”.?2?The average total POC in the study area was 2.06 g/kg,and the variation range is0.37?2.44 g/kg.In the soil layer of 0?30 cm,there were some differences in SOC content under different land-use patterns,which were paddy farmland>less than 3 years of abandoned land>vegetable land>3?8 years of abandoned land>8?10 years of abandoned land>economic forest land.As for the proportion of POC/SOC,the economic forest land and the 3?8 years of abandoned land and 8-10 years of abandoned land was low.In the vertical direction,it had a phenomenon similar to the total organic carbon in the soil.?3?The average values of MOC in the study area were paddy:farmland>less than 3years>vegetable land>3?8 years of abandoned land>8?10 years of abandoned land>economic forest land,which was related to the distribution of SOC content similar.As for the proportion of MOC/SOC,the farmland and vegetable land and less than 3 years of abandoned land was higher.In the vertical direction,except for the economic forest land,the content of MOC in other land-use patterns decreased with the increase of soil layer.?4?In 0?30cm soil layer,there are differences in the particle size composition of soil aggregates under different land-use patterns,Particularly,the content of aggregates with particle size>5 mm changed most obviously in farmland,which was indicated that human activities were more sensitive to aggregates with large particle sizes.The SOC content of soil aggregates is also different under different land-use patterns.The average values of soil aggregates in the study area were paddy:vegetable land>farm land>economic forest>land than 3 years>3?8 years of abandoned land>8?10 years of abandoned land,It shows that the years of abandoned land were not conducive to the accumulation of organic carbon in soil aggregates within 10 years.?5?In this study,the soil particle size composition was mainly composed of clay?21.23%?38.83%?,powder?16.38%?40.41%?and sand?58.81%?20.95%?.Except for economic forest land,the content of soil clay increased with the increase of soil depth,while the content of sand increased with the depth of soil.Correlation analysis showed that SOC content was positively correlated with soil clay content and grain content,while SOC was negatively correlated with sand content.?6?The average pH value shows economic forest land?5.68?>different years of wasteland?5.60?>vegetable land?5.53?>farmland?5.21?.Correlation analysis results showed that there was a negative correlation between SOC and pH in this study area.