The Characteristics Of Soil Organic Carbon Under Different Cultivation Patterns

As the discussion of climate change in the international government goes deeper,improving farmland capacity of soil carbon sequestration and emission reduction to cope with climate change has become the focus of the current scientific research.Organic farming is one of the important patterns of low carbon economy,which has huge potential in carbon sequestration and emission reduction.This paper focused on the characteristics of soil organic carbon in organic and conventional cultivation.Through positioning research,the dynamic change of soil organic carbon and its components under two planting patterns were compared.Through the aggregates gradation,the distribution features of soil organic carbon and its components in different aggregates and the physical and chemical mechanism of soil carbon sequestration were studied.The study also discussed the characteristics of soil organic carbon in the different areas in China between organic and conventional planting pattern.The above research was main to provide a theoretical basis that organic farming has the ability to respond to climate change,so as to promote the sustainable development of agriculture.The long-term study of soil organic carbon and its components under organic and conventional planting pattern show that soil physical and chemical properties had been improvedf after 10 years of organic farming.Organic matter,total nitrogen,available phosphorus and available potassium were higher than conventional farming.While conventional planting only improved organic matter and the nutrient indexes had different degree of reduce.The peroxidase and polyphenol oxidase activity were 2.66 and 0.98 mg theogallin g-1·2h-1 under organic farming,while the two enzyme activity were 1.64 and 0.67 mg theogallin g-1·2h-1 under conventional farming.The content of soil organic matter,heavy fraction of organic matter and labile organic matter under organic farming were higher than those under conventional farming and showed a trend of increase year by year,which from 21.52 g·kg-1,20.75 g·kg-1 and 5.93 g·kg-1 in 2004 to 30.94 g·kg-1,28.29 g·kg-1 and 7.83 g·kg-1 in 2013.The growth of organic carbon was slow in the early period of organic farming.After 5 years,it became fast.The organic matter under conventional farming began to showing a downward trend from 2009,and the heavy fraction of organic matter was decreased from 2011,while the labile organic matter was in a gentle increase.From the long-term location experiment,organic farming increased the content of organic matter and its composition and promoted soil enzyme activity,which promoted organic carbon transformation from the labile part to more stable part of humic acid.Combined with the differences of soil aggregates composition,distribution and organic carbon fractions between organic and conventional cultivation,the results show that the percentage of aggregates(>1mm,1?0.5 mm,0.5?0.25 mm and<0.25mm)in the conventional cultivation were 23.75%,15.15%,19.98%and 38.09%,while those in organic cultivation were 9.73%,18.41%,24.46%and 43.90%.The percentage of<0.25 mm micro-aggregates was significantly higher in organic cultivation than that in conventional cultivation.Organic cultivation increased soil organic carbon(average of 17.95 g·kg-1)and total nitrogen contents(average of 1.51 g·kg-1).Among the same aggregates in organic cultivation,the average content of heavy organic carbon fraction was significantly higher than that in conventional cultivation.This fraction accumulated in<0.25 mm micro-aggregates,which were main storage sites of stable organic carbon.In organic cultivation,the content of labile organic carbon in>1 mm macro-aggregates was significantly higher than that in conventional cultivation,while no significant difference was found among the other aggregates,indicating that the labile organic carbon was enriched in>1 mm macro-aggregates.Organic cultivation increased the amounts of organic carbon and its fractions,reduced tillage damage to aggregates,and enhanced the stability of organic carbon.Organic cultivation is therefore beneficial to soil carbon sequestration.The distribution regular of iron and aluminum oxides in various aggregates was not obvious,probably because iron and aluminum oxides chemical mechanism of organic carbon didn't play a major role in this farm.Characteristics of soil organic carbon in different areas under organic and conventional cultivation were different because of the difference of planting areas,planting crops,and planting years.Organic farming within 3 years of history in jintan,shanxi and yangzhou had no significant differences in organic carbon,heavy fraction of organic carbon and labile organic carbon compared with conventional cultivation(P<0.05).Organic farming within 4 to 6 years of history in Shanghai,Shandong and Yunnan had significant differences in organic carbon,heavy fraction of organic carbon and labile organic carbon compared with conventional cultivation(P<0.01).With the extension of organic farming history,the gap of C/N ratio between organic and conventional farming trends to expand.Both the two planting patterns had significant positive correlation between organic carbon and heavy fraction organic carbon,labile organic carbon.Compared with the conventional farming,along with the increase of the content of organic carbon,heavy fraction of organic carbon and labile organic carbon accumulated faster under organic farming,and the heavy fraction of organic carbon accumulated faster than labile organic carbon.