Effect Of Straw Returning On Characteristics Of Soil Organic Matter

Straw is an important organic fertilizer soil resources and is rich in nutrients necessary for crop growth.Straw directly or indirectly returned to the soil,can improve the soil water,heat and other environmental conditions.Thereby it also can increase crop yield.In the meantime,straw returning can tightly bind the decomposed crop straw with soil particles and increase soil carbon sinks.In this paper,three different experimental schemes were set up:the field experiment,and the straw in-situ transformation in the field experiment and small scale experiment.These experiments were used to study the effects on crop growth and soil organic matter and the effects of different storied soil depths on soil properties and some changes in the straw-soil interface.Conventional chemical analysis methods were used to analyse the chemical changes,and the use of elemental analysis.The change of humic acid structure was studied by means of elemental analysis? infrared spectroscopy and so on.The conclusions are as follows:(1)The results of field experiment in three consecutive years showed that there was no significant effect on the growth of maize roots and the yield of maize in the short period compared with conventional planting in the experimental region.The contents of soil organic carbon in the area of straw returning increased with the increase of straw application level,and there was no significant difference in soil organic carbon content in the planting area.There were no significant differences in the contents of humic acid and fulvic acid between the treatments,and the content of humin was increased with the increase of straw returning in the planting area.The contents of humic acid,fulvic acid and humin were increased with increase in straw application level to field.(2)Straw in-situ transformation in the field experiment showed that the total organic carbon,humic acid organic carbon,fulvic acid and humin organic carbon in the same depth soil layer increased with the increase of straw content,especially straw application rates of 2.64% and 5.28% treatments had significant effects on soil total organic carbon,humic acid carbon,fulvic acid and humin carbon content.With the increase of straw application rates,the content of microaggregates in the soil decreased gradually,and the content of macromolecules gradually increased.This indicated that the addition of straw was beneficial to the transformation of microaggregates to large aggregates and improved soil aggregates stability.The content of organic carbon in aggregates with > 2mm and 0.25-2mm was higher than that of 0.053-0.25 mm and <0.053 mm aggregates,and the proportion of organic carbon in the soil aggregates was increased in the soil.It can be seen from the results of the study that the B5 treatment has a significant effect on the increase of dissolved organic carbon and readily oxidizable organic carbon content in the 0-15 cm soil layer.In the 30-45 cm soil layer,the contents of water soluble organic carbon and carbon monoxide were significantly increased under the conditions of 1.32%,2.64% and 5.28% of straw,while the treatment with low amount of straw was not significantly affected.(3)Through the analysis of elemental composition,the addition of high amount of straw could contribute to the accumulation of carbon and nitrogen groups in humic acid and reduce the degree of condensation of soil humic acid.The addition of straw make humic acid molecules to the diretion of simplification and younger by means of differential thermal analysis.FTIR and fluorescence emission spectra analyses indicated that the addition of straw enhanced the aliphatic structure and decreased the aromaticity of humic acid(HA),that was to say that HA molecular structure approaches to the development of simplification and younger.(4)Under the field condition of straw in-situ transformation,the content of available iron in the soil was the highest,followed by the effective manganese andthe effective zinc,and the effective copper content was the lowest.The content of available manganese in the same depth decreased with the increase of straw application level.In the S2 and S3 layers,the maximum amount of straw was significantly affected the amount of available manganese.In the S2 layer,the content of available iron was decresed sifnificantly under B4 treatment in the soil,and the decrease was 5.61%.Only the available iron content significant change under B5 treatment in the S3 layer.Iron content increased by 5.51%.The available copper content was increased under B5 treatment in soils at 0-15 cm and 15-30 cm depth.In the S1 and S3 layers,the content of available zinc in the soil was significantly reduced by 33.72% and 31.13%,respectively.In the S2 layer,the content of available zinc in B5 was the highest,and significantly increased by 33.84 %.(5)Microscopic study showed that the soil properties in the straw-soil interface are quite different from the position of away from the straw layer,and there is a gradient change.After two years later of straw decomposition,the soil organic carbon components and microaggregates were significant change on the upper layers in the range of 2mm;In the lower layers,the soil total organic carbon was changed sifnificant within 10 mm,but the influence range on the organic carbon components were basically within 4mm.With the increase of the distance from the straw layer,the organic carbon composition of the soil showed a decreasing trend,while the soil properties away from the straw layer position did not change significantly.In general,the mode of plating and returning is more suitable for the current corn production requirements,and the growth and yield of corn were not affected.From different depths of straw returning,deeper soil returning may cause more organic carbon to accumulate in the soil layer,so that the straw can be more converted into humus and improve soil fertility.