| In order to pursue the high crop yield and high efficiency in agriculture production,increasing amounts of mineral fertilizer were applied.This caused higher production cost,as well as exerted pressure for soil environment.Straw returning is considered to be the most effective measure to improve the soil fertility and reduce environment pollution in agroecological system.Soil organic carbon（SOC）is the key of soil fertility.It is still the most concerning issue to assessing the effects of straw returning on SOC pools and the C sequestration ability.Currently,many studies were carried out to investigate the SOC propertied after straw returning in worldwide and Northeast China,but the comprehensive evaluation of SOC pool,fraction and stability under different straw returning methods still need to be documented.Based on short-term field experiment of different straw returning managements in the central region of Mollisol,soil samples were collected at 0-20 cm surface soil and 20-35 cm subsurface depths.The water-stable aggregate and density fraction method and Fourier Infrared Spectroscopy（FTIR）methods were utilized to unreal the characteristics of infrared spectrum of organic carbon in both bulk soil and aggregate-sized fractions under different straw returning managements.In addition,a30-day incubation experiment was also conducted to evaluated the C mineralization ability of the different soils after 4-years continuous straw returning.The six field treatments were:（1）S0,tillage 20 cm,mineral fertilizer without straw returning.（2）S1,tillage 20 cm,straw returning at 5 t ha-1plus mineral fertilizer.（3）S2,tillage 20cm,straw returning at 10 t ha-1plus mineral fertilizer.（4）S3,tillage 35 cm,straw returning at 10 t ha-1plus mineral fertilizer.（5）S4,no-tillage,straw mulching at 10 t ha-1plus mineral fertilizer.（6）S5,tillage 20 cm,straw burning at 10 t ha-1plus mineral fertilizer.The results are as follow:（1）After 4 years of straw returning,the arable Mollisol SOC pool and SR increased significantly.Compared with S0 soil,the SOC pool at surface soil（0-20 cm）increased by 9.00%,17.15%and 22.94%in S1,S2,S4 treatments,respectively.There were no significant differences among S3,S5 and S0 treatments.Compared with S0soil,the SR increased by 94.0 kg C ha-1year-1、114.0 kg C ha-1year-1、41.8 kg C ha-1year-1、152.40 kg C ha-1year-1and 41.4 kg C ha-1year-1,respectively from S1 to S5treatments.At subsurface soil（20-35 cm）,the SOC increased by 3.57%,6.22%,9.31%,3.50%and 3.97%from S1 to S5 treatments,respectively,when comparing with S0.The SR increased by 54.27 C ha-1year-1,94.64 kg C ha-1year-1,141.51 kg C ha-1year-1,50.93 kg C ha-1year-1and 60.36 kg C ha-1year-1,respectively.（2）Similar to the SOC,the OC fractions at the surface and subsurface soils changed after 4 years of straw returning practices.At 0-20 soil depth,the contents of OC of liable fraction,free light,occluded light and heavy fractions followed the order of S2>S1>S4>S5>S3>S0.At the 20-35 soil depth,the contents of OC of liable fraction,free light,occluded light and heavy fractions followed the order of S3>S2>S1>S5>S4>S0.All the OC contents were higher in surface later than those in subsurface layer,with the exception of higher OC contents in subsurface layer in S3treatment,dut to deep returning of crop straw in this treatment.The results showed that straw returning was beneficial to the accumulation of different OC fractions,and the effect at surface depth was more significant than subsurface layer.The differences of OC contents among different straw returning practices indicated that the quality,and quantity of the OC amendments,as well as soil tillage together have significant influence on the OC dynamics.（3）There were significant differences in the mass fraction and contents of OC of aggregates in different particle sizes at surface soil（0-20 cm）and subsurface soil（20-35 cm）under different straw returning managements.The mass fraction and contents of OC of macroaggregates（>2 mm and 2-0.25 mm）and mean weight diameter（MWD）were significantly increased by straw returning compared to the applying mineral fertilizer alone,and there were also significant differences between different straw returning treatments,but applying mineral fertilizer alone treatment the mass fraction and OC contents of microaggregates,silt and clay were significantly higher than that of straw returning treatments.Based on the analysis of particle size mass fraction and OC contents of all treatments,we concluded that straw returning treatments were beneficial to the enrichment of microaggregates,silt and clay organic carbon to macroaggregates with high resistance to erosion that was beneficial to SOC sequestration.（4）The Fourier Infrared Spectroscopy（FTIR）methods of bulk soil and aggregate-sized fractions showed that straw returning to the field increased the proportion of aliphatic carbon functional groups,decreased the proportional of aromatic carbon functional groups.Correlation analysis and principal component analysis showed that the content of organic carbon showed significantly positive correlations with the relative peak area of aliphatic within bulk soil and>0.25 mm aggregates,but significantly negatively correlations with the relative peak area of aromatic（P<0.05）.On contrast,the organic carbon contents were significantly negative correlated with the relative peak area of aliphatic group and positively correlated with the relative peak area of aromatic group within<0.053 mm aggregate（P<0.05）.These results indicated that the organic carbon within macroaggregates were mainly composed of simply-structured and easily-decomposed organic matter,while the organic carbon within microaggregates were mainly composed of aromatic carbon with higher stability.Short-term straw returning.The 20 cm soil tillage combined with crop straw returning at 10 t ha-1was proposed to be the most effective measure to increase the formation of macroaggregates and the content of aliphatic carbon,increased the surface SOC and its stabilization,and benefit to carbon sequestration and stabilization.（5）After 4 years of straw returning,the yield followed the order of S2(8134 kg ha-1)>S1(7940 kg ha-1)>S5(7833 kg ha-1)>S0(7760 kg ha-1)>S3(7405 kg ha-1)>S4(6673 kg ha-1).Compared with S0 soil,the yield increased by 2.32%,4.81%and0.94%from S1,S2 and S5 treatments.The yield decreased by 4.79%and 16.28%from S3 and S4 treatments.（6）It was found that the SOC mineralization of 5 different straw returning treatments under the condition of exogenous organic matter addition in the whole incubation stage showed three stages;sharp rise,sharp decrease and gentle fluctuation.The cumulative mineralization showed a trend of rapid rise first and then slow rise.Compared with no fertilizer treatments,the cumulative mineralization of rate decreased by 10.21%,14.07%,38.92%and 4.24%from S0,S1,S2 and S5 treatments.The activity of soil sucrase and urease followed the order of S2>S1>S5>S0>CK.（7）The principal component analysis results showed that S2 treatment had the best effect on the SOC pool,contents of OC and stability of different fractions at surface soil（0-20 cm）,S3 treatment had the best effect on the SOC pool,contents of OC and the stability of different fractions at subsurface soil（20-35 cm）.The main influencing factors include contents of TOC content,total nitrogen,liable fraction carbon,light fraction organic carbon,the mass fraction and contents of OC of large macroaggregate,small macroaggregate and mean weight diameter.S0 treatment had the worst effect,and the main influencing factors were soil bulk density,the mass fraction and contents of OC of microaggregate,silt and clay.Conclusion:In total,different straw returning managements will have important influence on the SOC pool,the contents of different fraction OC,the stability and mineralization process of an arable Mollisol,and the degree of influence was different in the surface and subsurface soil,revealed that the content and stability mechanism of an arable Mollisol SOC in different straw returning managements were different,and it was preliminarily obtained that tillage 20 cm,straw returning at 10 Mg ha-1year-1plus mineral fertilizer was the best method at surface soil（0-20 cm）,deep tillage 35 cm,straw returning at 10 Mg ha-1year-1plus mineral fertilizer was the best method at subsurface soil（20-35 cm）.The results are expected to provide some theoretical basis for optimizing straw returning managements. |
PDF Full Text Request