Study On Aggregate Formation And Its Carbon Sequestration Driving Mechanisms For Grey Desert Soil Under Long-term Fertilization

The grey desert soil is a typically cultivated soil of arid inland regions in northwestern China. In recent years, grey desert soil was severely damaged due to vegetation degradation,the biodiversity decline, etc, which results in the destruction of soil structure and the decline of soil productivity. They have seriously restricted the sustainable yield of the grey desert soil in Xinjiang, China. In order to enhance the soil structure and improve the biodiversity and abundance, the grey desert soil from the northwest arid desert zone was the foundation for this study, using the long-term located fertilization experiments of Chinese National Soil Fertility and Fertilizer Efficiency Monitoring Base of Grey Desert as the experiment plot, and to study the relativity among the soil aggregation, intra-aggregate carbon molecular structure and the community of soil fauna with aggregate formation. The distribution, content and variations of these soil organic carbon pools in different fertilizer treatments on long-term located fertilization in grey desert soil area were analyzed. Then the correlation between different soil organic carbon pools and soil fertility was explored for improving the farmland productivity of the grey desert soil and realizing the sustainable development of regional agriculture. The main research results as follows:Macroaggregates and the free silt + clay fraction were more sensitive to fertilization and the shifts in the stored C towards microaggregates may play important roles in soil aggregation and soil organic carbon sequestration in grey desert soils. The application of manure accelerated the accumulation of soil organic carbon content, particularly by increasing the amount of C in the fine intra-aggregate particulate organic matter(iPOM) rather than the coarse iPOM or the silt + clay subfraction and the effect was more obvious than crop residues returned to the field. The mineral fertilizer(N and NPK) applied could only sustain the soil organic carbon content, however, they had no significant effect on the soil aggregation. These results indicated that the soil organic carbon played an important role in the stability of macroaggregates with aggregate formation and improving the soil fertility.The wet-sieving method was used for analysis of molecular structure of the organic carbon in the soil and the aggregates on the solid-state13C-nuclear magnetic resonance(13C-NMR) spectroscope. The result indicated that the ratio of alkyl-C/O-alkyl-C increased and the percentage of O-alkly-C and aromatic-C decreased with decreasing aggregate size.These findings indicate that the more the organic carbon therein decomposed with the finer the aggregates. Compared with no fertilizer treatment(CK), treatments 1.5MNPK and SNPK increased the ratio of O-alkly-C and Carbonyl-C to total organic carbon in soil and Carbonyl-C were accelerated in macroaggregates and microaggregates. The mineral fertilizer(N and NPK) applied increased the percentage of alkyl-C and the ratio of alkyl-C/O-alkyl-C,but decreased the ratio of aromatic-C and Carbonyl-C. These findings indicate that the more the organic carbon therein decomposed with the mineral fertilizer applied. These findings from the study indicated that long-term application of organic manure and crop residues helps protected physically the large content of carbohydrates and organic acids with manure and crop residues carries in to the macroaggregates and microaggregates, thus improving the content of organic carbon in soils.The relationship between soil fauna community and different fertilizer management practices is significant. The application of organic fertilizers(i.e., sheep manure or crop residues) promoted the number of individuals and species of soil fauna owing to the exogenous organic matter that fertilizers provided for the survival and development of soil fauna. However, the balanced mineral fertilizer(NPK) treatment could only sustain the richness of the soil fauna community. The individuals and H’ of the soil fauna community were significantly correlated with the organic C concentration in the free silt + clay fraction and macroaggregates. These findings from the study indicated that soil aggregates provided more food and energy resources for soil fauna communities. Meanwhile, the diversity of soil fauna communities could accelerate the soil aggregate formation.During 24 years of application of organic fertilizer(1.5MNPK), the total soil organic carbon and organic carbon pools in grey desert soil were significantly increased with time.Sand-organic C(S-OC) was more sensitive to fertilization and the amplitude of S-OC had a larger increase than other fractions. The free particulate organic matter(cfPOC + ffPOC) were more sensitive to the changes of soil fertility. However, the intra-particulate organic carbon(iPOC) in microaggregates played a key role in soil major elements applied and soil organic carbon sequestration.