Effects Of Straw Addition On Organic Carbon Fixation And Distribution In Brown Earths With Different Fertility Levels

Soil organic carbon?C?is the main element of soil quality.It plays a significant role in the maintenance of soil fertility and agroecosystem.Straw returning can increase soil organic carbon?SOC?content and promote the formation of large aggregates.The organic C pools of soils under different fertility levels would be affected by the amounts of straw returning to soil.However,it is not clear that the distribution and fixation of organic C in aggregates of brown earth with different fertility levels affected by changes of straw residue amounts.The purpose of this study was to investigate the effects of the amounts of maize straw returning on organic C fixation and turnover in the different fertility level soils.The higher and lower fertility level soil samples were collected from the Long-term?27a?Located Brown Earth Experiment Station of Shenyang Agricultural University,Liaoning Province,China.The ¹³C-labeled corn straw was added to soil at the dosages of 0%,1%,3%,5%and 10%and incubated for a year.The soil aggregates were divided into three classes?>0.25 mm;0.053-0.25 mm;<0.053 mm?by wet sieving method.By analyzing the dynamics of“new”C?from added maize straw?and“old”C?from soil?contents in aggregates of brown earth with high and low fertility levels,the effects of straw addition on the fixation and the distribution properties of new and old organic C in brown earth have been pointed out.The main results are as follows:?1?Soil C sequestration was affected by straw addition and different fertility levels.The results showed that:when the amount of straw was less than 1%,the C sequestration in high-fertility soil was more than that in low-fertility soil.Because long-term fertilization had made the SOC increase steadily,and a small amount of straw C has only decomposed quickly by the more microorganisms in the high-fertility soil.When the amount of straw was more than 1%,the C sequestration in low-fertility soil was more than that in high-fertility soil,since the organic C content in low-fertility soil itself was limited,and the saturation deficit was larger,so the C sequestration in low-fertility soil is potential.?2?The amount of straw added and the level of soil fertility have a common impact on soil C sequestration.The C sequestration efficiency in low-fertilizer soil increased with the increase of straw addition.The C sequestration efficiency of high-fertility soil was the highest in the addition of 1%,and the lowest was in the 5%addition.There may be C saturation of high-fertility soil.Due to the difference of organic C content,the C fixed efficiency of high fertility soil gradually decreased with the increase of straw addition,and the mineralization decomposition of old organic C increased.?3?The mass distribution of aggregates was significantly affected by straw addition and soil fertility levels.The Mean Weight Diameter?MWD?of aggregates increased significantly in low-fertility soils with the addition of more than 5%.And the MWD value of aggregates in high-fertility soils increased significantly after the addition of straw?P<0.05?.?4?The addition of straw significantly increased the organic C content of macroaggregates in soil.The SOC distribution in aggregates was significantly affected by the mass distribution of aggregates.The results showed that the total SOC was greatly affected by the rates of straw C addition within 180-day incubation,and the straw C was accumulated most in the large aggregates.With the decrease of aggregate size,the straw C contents decreased in the aggregates.The content of organic C in the macroaggregates treated with 5%and 10%increased significantly,and the organic C content in 0.053-0.25 mm granular decreased significantly,which was significantly affected by the distribution of aggregates.Large aggregates in high and low-fertilizer soils with 10%addition have higher fixation efficiency for straw C,and still had a certain C sequestration potential.?5?Increasing the input of straw C reduced the Mean Residence Time?MRT?and accelerated the turnover of SOC pool.The content of organic C in large aggregates has a great influence on soil MRT values,and the MRT values of the treated aggregates increased with the decrease of aggregate size.When the amount of straw was less than 10%,the effect of straw addition on the stability of organic C in low-fertility level soil was greater than that in high-fertility level soil.In the long term,the high-fertility soils were more conducive to SOC sequestration.