| Black soil was well known as organic matter-rich soils with high fertility. With the land use conversed from natural vegetation to arable land, low organic materials input resulted in the significant decline of soil organic matter (SOM) content and soil fertility, which caused serious agricultural and ecological problems. Use of organic amendments is generally seen as a key issue for promoting quantity and quality of SOM through application of greater organic materials, and organic amendments with different origin and rates markedly affected transformation and accumulation of SOM, which would result in variation in the dynamics, fractions and structure characteristics of SOM in soils. Based on the long term fertilization experiment subjected to farmland of typical black soil, the objective was to examine the difference between different origin and rate of organic amendments application management to investigate how they influence the SOM dynamics, SOM fractions separated by physical and chemical fractionation, and structure characteristics of SOM in soils. This work provided valuable information for illustrating SOM stabilization mechanism and establishing sustainable black soil management systems to maintain and enhance soil quality. The conclusions were as follow:Soil organic carbon (SOC) dynamics were significantly influenced by application of organic amendments with different kinds and rates. During10-year period of organic amendments application, SOC in plots with application of chemical fertilizer plus crop straw (NPKS) maintained at a stable level over time, however, SOC content in plots with application of chemical fertilizer plus pig manure (NPKM) gradually promoted over time, compared with the initial value, SOC content in NPKM increased by3.7%at the end of the studied periods. During10-year period of organic amendments application, SOC content in plots with application of chemical fertilizer plus pig manure at rates of7.5t ha-1yr-1(OM1) and15t ha-1yr-1(OM2) both increased slowly over the first three years, then accelerated the rate of growth, and maintained at a stable level over the last three years. However, SOC content in plots with application of NPK plus pig manure at rates of22.5t ha-1yr-1(OM3) showed a pronounced increase over the first three years, then remained a high stable level over the later periods. At the end of the studied periods, SOC content in OM1, OM2and OM3increased by4.37%,7.10%and13.9%respectively. Furthermore, there was evidence of linear correlation between SOC stocks and pig manure input (P<0.01). Results suggested that compared with NPKS, NPKM resulted in greater accumulation of organic carbon, and it was an effective way to increase input of pig manure for higher SOC content.Content of soil labile organic matter fractions were much higher in the treatments including organic amendments than applications solely of chemical fertilizers. Content of soil labile organic matter fractions may be affected at various extents on dependence of the kinds and rates of amendments. Compare with treatments of applications solely of chemical fertilizers (NPK), higher content of particulate organic matter (POM), light fraction organic matter (LFOM), biomass carbon/nitrogen (MBC/MBN), water-soluble organic matter (WSOM) was found in plots with application of chemical fertilizer plus organic manure, while leading to corresponding increase in the proportion of C and N content of each fractions in SOC and TN. Treatments with organic amendments application also increased the content of heavy fraction organic matter, but its proportion decreased significantly, which suggested that more N and C were incorporated into labile fractons than into recalcitrant fractions. Compared with NPKS, much greater content of each labile organic matter fraction were found in NPKM. With the increase of organic manure input, content of each labile organic matter fraction gradually promoted. The results suggested that application of chemical fertilizer amended with pig manure benefited for enhancing pool of labile organic matter fractions, and higher input of pig manure would significantly promote stocks of labile organic matter.Distribution of carbon, nitrogen and humic substances fractions in each aggregate fraction were influenced in different ways and at various extents on dependence of the kind and rate of amendments. Proportion of macro-aggregates (2-0.25mm) was highest, which accounted for about65.6-72.8%of the dry soil weight. Application of organic amendments increased proportion of macro-aggregates (>0.25mm) and mean weight diameter of aggregates (MWD) relative to NPK. Proportion of macro-aggregates (>0.25mm) in NPKM was2.6%higher over that of NPKS. With the increase of pig manure input, the MWD value increased gradually, and the MWD value in OM3was1.16. Carbon and nitrogen stocks within each class of aggregate decreased in the order:[0.25-0.053mm]>[2-0.25mm]>[>2mm]>[<0.053mm], Proportion of carbon and nitrogen stocks in macro-aggregates (>0.25mm) account for74.7%and77.3%of SOC and total nitrogen in bulk soil, respectively. Application of organic amendments significantly increased contents and stocks of carbon and nitrogen in macro-aggregates (>0.25mm) relative to NPK. Carbon stocks in two classes of macro-aggregates (>2mm and2-0.25mm) promoted gradually with the increase of pig manure input. Significant correlations between each of them and pig manure input were found (P<0.05). Proportion of humic acid (HA), fulvic acid (FA) and humin (HU) of each aggregate in content of bulk soil HA, FA, HU (PHA, PFA and PHU) decreased in the order:[2-0.25mm]>[0.25-0.053mm]>[>2mm]>[<0.053mm]. NPKM contributed greater content of HA and HU in each class of aggregates, and NPKS contributed greater content of FA. The PHA, PFA and PHU in each aggregates remained unchanged in treatment of OM1, but OM2and OM3treatment significantly increased the PHA, PFA and PHU of macro-aggregates (>0.25mm), but declined the PHA, PFA and PHU of micro-aggregates (<0.25mm).Structural properties of HAs were influenced in different ways on dependence of the kind and rate of amendments. HA in plots with application of organic amendments were characterized by lower degree of condensation, degree of oxidation and aromaticity, higher aliphatic character than HA from NPK treatment. HA from NPKS treatment featured higher degree of condensation, aromaticity, and aliphatic character than HA from NPKS treatment. With the increase of pig manure input, degree of oxidation of HA gradually decreased, and aliphatic character gradually increased, HA structure tended to become simpler and more aliphatic.Therefore, application of chemical fertilizer combined with pig manure was the most effective practice for promoting quantity and quality of SOM, and greater labile organic matter fractions and more aliphatic character was showed in SOM from soils amended with high input of pig manure.
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