Dynamic Characteristics Of Soil Organic Carbon And Nitrogen Under Different Land-Use Patterns And Their Biological Mechanism

Agricultural management influences the "sink" or "source" of arable soil as greenhouse gases. The systemic studies on dynamic characteristics and stabile mechanisms of soil organic carbon (SOC) and nitrogen (N) under different land-use patterns are important, which help to calculate the capacity of soils minerals to stabilize organic carbon and study the techniques of cultivating soil productivity. Based onto the physical, chemic and microbial theory of SOC protection, long-term experiments in arable soils were utilized to study the effects of different tillage (that is, tillage, no-tillage, mini-tillage), cropping (that is, field fallow, continuous maize cropping, maize-soybean rotation, continuous soybean cropping) and fertilization (that is, no fertilization, NPK, NPK+Straw, NPK+Manure, NPK+Manure+crop rotation) on the contents of SOC and total nitrogen (TN) in1m depth soil profile. Moreover, the integrated experiments of tillage, cropping densities and fertilization of spring maize were used to study the effect of managements on precursor substances (e.g. root residues) contributing to SOM formation. The response of SOC storage to agricultural management was evaluated in climate change context. The techniques of increasing C and N in soil were primarily chosen according to crop yield. The detailed results were as follows.The results of long-term tillage experiments indicated that mini-tillage has increasing C sequestration in the1m soil profile but no-tillage is in the topsoil, when compared to tillage treatment. Compared to tillage, nitrogen content in1m soil profile in mini-tillage had a significant decrease by over13.5%, but no significant difference in no-tillage was found. The C/N ratio was significantly higher in the topsoil in no-tillage and in the1m depth soil profile in mini-tillage as compared to tillage, which led to the slower decomposition rate of SOC in corresponding soil depth in no-tillage and in mini-tillage to advantage soil C sequestration. Mini-tillage is a better technique to C sequestration than no-tillage, but disadvantages N enrichment.The results of long-term cropping experiments indicated that rational cropping practices had more C and N accumulation than farmland fallow (FALL). The dominant aggregates in the FALL and three cropping practices were macro-sized aggregate (>0.25mm) and the<0.25mm sized fractions, respectively. The cropping practices sustained greater stable organic carbon storage than the FALL. Under plus manure application, continuous maize cropping (CMC) had a greater C storage in lm soil profile than maize-soybean rotation (MSR) and continuous soybean cropping (CSC). The CMC can sequestrate more C than the other three patterns, which led to the increase of stable and instable SOC storages. So, the greater instable SOC storage in the CMC had a higher sensitivity to environment change than the other practices.The results of long-term fertilization experiments indicated that straw manure application (SMA) increased SOC and TN accumulation in the0-40cm depth soil. Compared to no-fertilization treatment, no significant C accumulation was found in inorganic fertilizer (NPK) and straw returning (NPKS) application treatments, however they obviously increased TN contents. Fertilization application significantly increased easily oxidized organic carbon (EOC), in which SMA and NPKS had better EOC increment. SMA and NPKS advanced the C levels contained in aggregates, but dropped the stability of SOC storage. Resultantly, SMA can be utilized to increase SOC accumulation and agricultural productivity, but there was poorly C sequestration for NPKS and NPK applications in rainred soil in Northeast China.The results of integrative experiments of tillage, cropping densities and fertilization of spring maize indicated that the significant quadratic function were found between maize yield and root biomass in the0-60cm soil profile, indicating that root residues can be computed with the maize yield. The effects of ridge in fertilizer topdressing on root biomass and its distribution in soil profile were mainly restricted by moisture factor. The increasing density of maize advanced root residue. Commonly, the adding fertilization level would increase root biomass. The fitting cropping density and fertilization application can increase maize yield and root residue input to soil. Generally, a large root residue input to soil will redound to SOC sequestration.