Biological Properties And Physical Protection Of Soil Organic Matter Of Paddy Soil Under Different Organic Management Practices

Soil organic matter (SOM) as well as its effects on biological activity and diversity plays an important role in agricultural sustainability. Organic management practices are central to the increase of SOM level. However, only few long-term reports mentioned the impact of different organic amendments management practices on the SOM and biological properties of paddy soil in subtropical region. This study sampled soil from long-term rice field experiments located in Jiangxi province of China in the year of 2003. The experiment was established since 1981 including treatments of the quantity, quality and the time of organic matter amendment, including seven organic matter treatments such as 1500kg green manure amending before early rice seeding (Tl), 3000kg green manure before early rice seeding (T2), 1500kg green manure and 1500kg pig manure both amending before early rice seeding (T3), 1500kg green manure before early rice seeding and 1500kg pig manure amending after early rice harvest (T4), same with T4 and 300kg rice straw amending just before winter (T5), same with Tl and 300kg rice straw amending just before winter (T6), same with Tl and 300kg rice straw amending after early rice seeding (T7), additionally two controls being chemical fertilizers only (T8) and with nothing amending (T9).The objectives of this dissertation research were to compare the influences of different organic management practices on 1) soil microbial biomass, activity and plant available soil nutrients; 2) soil enzyme activities involved in carbon, nitrogen and phosphorus cycling; 3) soil microbial community composition, functional diversity and microbial nutrient limitation; 4) soil mineral composition and Fe/Al oxides content; 5) aggregate stability and SOM fractions separated by physical fractionation. Firstly, I hope to evaluate the long-term organic management practices on soil biological properties which are critical to soil quality; Secondly, I hope to find the trends of structure stability and SOM fractions change under different organic management practices, especially the labile SOM which is usually thought as sensitive indicator of SOM development; Finally, and the most important, physical protection mechanisms of SOM stabilization for paddy soil are explored.Compared with both the unfertilized and chemical fertilized treatments, there were significant increase of soil microbial biomass carbon, nitrogen and phosphorus, basal respiration, mineralizable carbon, nitrogen, and available nutrient in the organic matter amendment plots. Also, significant differences between the organic matter amendment treatments showed the profound effects of quantity and quality of organic matter inputs. In addition, the above microbial and nutrient variables showed strong seasonal dynamics, with the highest value being on July when the soil temperature was highest and soil moisture was lowest of the year. Although the seasonal variation, the different organic management predominated the influence.Similarly, the soil enzyme activities also changed dramatically under different organic matterpractices. Enzyme activities associated with carbon, nitrogen and phosphorus cycling, such as β-glucosidase, invertase, xylanase, cellulase, phenol oxidase, peroxidase, protease, urease, asparaginase, arginine deaminase, glutaminase, histidine ammonia lyase, acid phosphatase, neutral phosphatase and general FDA hydrolysis almost all did increase under organic matter amendment practices. The quality of organic matter have larger impact than the quantity and the amendment time, with the pig manure showed the greatest promoting effects, and green manure only amendment would repress the phenol oxidase activity.The functional diversity obtained from enzyme activities also differentiated obviously the different organic management practices, particularly the distance was large between the organic matter fertilized treatments and the chemical fertilized and the unfertilized treatments on the principle component analysis (PCA) plots. The xylanase activity was the most potential...