Effect Of Fertilization On Quantity And Structural Characteristic Of Humic Acid In Soil Aggregates

As we all know, the long-term sustainable development of soil is closely related to people’s life, it has become a major global concern. Currently, there are some serious problems, such as soil fertility declining and straw burning, which have affected people’s daily lives. To protect the soil organic matter content so that it will not decline further, get a long-term accumulation of soil organic carbon, experts and scholars launched a number of studies from organic fertilizer aspects, expected to improve soil quality through organic fertilizer to improve soil fertility. Current situation: At present, the studies about the surface soil are more, while the research about subsurface are less; the studies that applying organic material and manure to soil are more, while the research that returning cropstalks to the field and adding horse manure to soil for long-term are less; the total soil research are more, while the studies about structural characteristics of humic acid for different size aggregates are less. For the current study, we studied the long-term return cropstalks to the field and chemical fertilizer on the effects of aggregates compositions by means of wet sieving in this paper; this article studies the long-term return cropstalks to the field and chemical fertilizer on the effects of total soil and the organic carbon accumulation with different fractions of aggregates by applying humus composition modification method; we studied that the effects of different fertilizer and organic manures application countermeasures on quantity and structural characteristics of HA in soil aggregates; by using elemental analysis, infrared spectroscopy and thermogravimetric analysis, In order to providing theoretical basis for soil rational fertilization, soil fertility improvement and rational utilization of straw resources. Research conclusions basically have the following several aspects:(1) Composition of aggregatesThe advantages fraction is at 2~0.25 mm and 2~0.25 mm respectively, corresponding to the surface and subsurface of black soil. The application of straw with chemical fertilizer increased the large aggregates content of the surface soil at 2~0.25 mm, and the content of powder-clay component <0.053 mm decreased, but had no significant effect to composition of aggregates in soil subsurface.(2) Accumulation of organic carbon Whether it is the surface or subsurface, the amount of SOC in black soil is highest, whose size of large aggregates is more than 2mm. The amount of SOC at surface soil and all levels of aggregates were aggrandized by the application of straw with chemical fertilizer which had no significant effect to the amount of aggregates in subsurface soil and its aggregates.(3) The quantity of HACompared with soil in surface, the soil in subsurface and all levels of aggregates had lower content of HA. In the treatment of CKd, the content of HA decreased as the reduction of aggregates size in black soil. While in the treatment of FS, the distribution of HA at all levels of aggregates was: >2 mm> 2~0.25 mm(<0.053 mm)>0.25 ~0.053 mm. The application of straw and chemical fertilizer significantly increased the amount of HA in surface soil and all levels of aggregates.(4) The structure of HAThe content of HA, H, N and O in black soil and dark brown soil were respectively among 560~600 g·kg-1, 50~80 g·kg-1, 40~60 g·kg-1, and 290~310 g·kg-1. The mole ratios of H/C, N/C and(O+S)/C were respectively among 0.9~1.7, 0.06~0.08, 0.38~0.41.Compared with HA in different soil, the condensation degree of HA molecule in black soil was higher than in dark brown soil, and had higher proportion of carbon in aliphatic chain hydrocarbon, longer carbon chain, stronger hydrophobic, and more mature and stable.In terms of different soil layer, the condensation degree of HA molecule in subsurface soil was higher than surface, and more mature and stable, which also showed the aging of HA in subsurface soil. the application of organic fertilizer can’t be limited to traditional surface 0~20cm operations, also it is very urgent to apply organic manure into subsurface 20~40cm to conduct fertility, which is one of that we proposed "straw deep application"Compared with different fractions of aggregates HA, the large aggregates had lower condensation degree, and more youth and active; the small aggregates had higher proportion of carbon in aliphatic chain hydrocarbon, stronger hydrophobic and more mature and stable.Between different treatment of fertilization, the H/C mole ratios of HA in surface and subsurface decreased with the application of straw with chemical fertilizer or horse manure with fertilizer; the proportion of 2920/1720 and 2920/1620 rises; the high-temperature heat, hot weightlessness and the ratio of high temperature and low temperature of weightlessness were increased, which illustrated that long-term application of organic manure with chemical fertilizer can increase the condensation degree of HA molecule, and enhance the proportion of carbon in aliphatic chain hydrocarbon, hydrophobic and thermal stability, at the same time, make HA more mature and stable, and conducive to the accumulation of organic carbon.In summary, the HA in black soil had higher condensation degree, more maturely and stable; the HA in subsurface soil is relative aging than surface, and the application of organic fertilizer can’t be limited to traditional surface operations, also it is very urgent to apply organic manure into subsurface to conduct fertility; the large aggregates had lower HA condensation, more dynamic; long-term application of organic manure with chemical fertilizer can increase the degree of condensation of HA molecules that make humic substances more mature and stable, conducive to the accumulation of organic carbon.