Microbiological Features Of Soils Under Different Fertilization Systems And Their Related Soil Fertility

Soil microorganisms are the driving force of soil nutrient transformation and circulation. Soil biological fertility is the core of soil fertility. As basic units of soil structure, soil aggregates are the locale where soil nutrients transform and circulat and they are closely correlated with soil fertility. This dissertation is based on the long-term fertilization experiments in"Beijing Fluvo-aquic Soil Fertility and Fertilizer Efficiency Long Term Monitor Base (BFSFFELTMB, founded in 1990)". There are 13 different treatments available here, which were established in 1990. Six treatments were selected to conduct this doctoral research project. Among the six treatments, four were in a wheat-maize rotation system with (1) no fertilizer application (CK), (2) mineral fertilizers application (NPK), (3) mineral fertilizers plus farmyard manure application (NPKM) and (4) mineral fertilizers with maize straw incorporated application (NPKS). The fifth treatment was in a wheat-maize/wheat-soybean rotation system with NPK application (NPKF). The final treatment was deserted arable land (CK0) with weeds growing. The amount of chemical fertilizer applied per year was N 150 kg·hm^-2, P₂O₅ 75 kg·hm^-2, K₂O 45 kg·hm^-2, manure 22.5 t·hm^-2 and maize straw 2.25 t·hm^-2. Through using dry sieving method, six different aggregates were obtained, which were >5mm, 2-5mm, 1-2m, 0.5-1mm, 0.25-0.5mm, and <0.25mm in size while through using wet sieving method, another four different aggregates were collected with different size of >2mm, 0.25-2mm, 0.053-0.25mm, and <0.053mm. Biological properties and relevant soil fertility under different long-term fertilization systems were thoroughly studied. This research provides a theoretical basis for cultivation and construction of soil biology fertility. The following results were obtained in this study:1. The soil nutrient content and the yield of crops were low with long-term (16 years) no fertilizer application (CK) treatment. Compared CK, the physicochemical property of soil improved and the yield increased in long-term fertilizer application treatments. Under different fertilization systems, the content of :he soil organic matter, total N, total P and available phosphorus in long-term NPKM were the highest. The pH value and bulk density of soil decreased slightly with the treatment of NPKM in Fluvo-aquic Soil. Contrast to NPK treatment, the NPKF and NPKS treatments significantly improved the nutrient content and their pH value and bulk density decreased slightly. The application of phosphoric fertilizer and organic fertilizer played an important role in the process of increasing yield of crops in Fluvo-aquic Soil.2. The soil organic C(SOC)and total N( STN) content, microbial biomass C(SMB-C) &N(SMB-N), activities of soil invertase, phosphatase and urease, and the ratio of SMB-C/SOC and SMB-N/STN were found higher in long-term (16 years) deserted arable land than those in cultivated arable land soils. However, the soil metabolic quotient, pH value and bulk density of fallow soil were lower than those in cultivated arable land soils. The soil nutrient concentration, microbial biomass C & N, activities of soil invertase, phosphatase and urease, were higher in treatments with fertilizer application (NPK,NPKM,NPKS and NPKF) compared to CK. The soil parameters investigated above were also found higher in wheat-maize/wheat-soybean rotation cropping system compared to continuous wheat-maize cropping system. Among the four fertilizer application treatments (NPK,NPKM,NPKS and NPKF), NPKM had relative higher soil nutrient concentration, microbial biomass C&N, and enzyme activities. However, the soil metabolic quotient, pH value and bulk density of NPKM were lower than those in the remaining three treatments.3. The community structure of bacteria microorganisms was assessed by denaturing gradient gel electrophoresis (DGGE) and Unweighted Pair Group Method Clustering (UPGMC) analysis of the DGGE banding patterns showing that the bacterial community structure was affected by different treatments. Compared with CK, the results indicated a significant increase in microbial diversity by fertilization treatments. However the composition of the bacterial community in NPKM treatment was more complex than that in others. Cluster analysis of the DGGE profiles showed that bacteria in the six soil samples were divided into three clusters. Bacterial communities in CK and NPK soil samples belonged to one cluster, those in NPKF and CK0 soils to another cluster, and that in NPKSt and NPKM soil to a third single cluster. The similarity of bacterial community in soils with six different treatments was 53%. This research demonstrated that mineral fertilizer applied with farmyard manure at the same time could increase both biomass and diversity of bacterial community in soil.4. The experiment of using dry sieving method to obtain soil aggregates showed that the long-term fertilizer application helped increase the percentage of aggregates in the size groups of 2-5mm, 1-2mm, 0.5- 1mm and 0.25-0.5mm. It suggests that long-term application of chemical fertilizers with organic manures may fercilitate the formation of these four types of aggregates. This indicates that long-term application of organic manures is beneficial to the aggregate formation of soil macro-aggregates.The contents of SMB-C, SMB, soil organic C, total nitrogen and total phosphorus in different size groups were found significantly different. The group of 0.25-0.5mm size was found the highest and the group of <0.25mm size was found the lowest in all soil samples. The long-term fertilizer application was found in favor of increasing nutrient contents and storage capacities in the groups of 2-5mm, l-2mm, 0.5-1mm and 0.25-0.5mm sizes. Under all fertilized treatments, the contents and storage capacities of nutrient were significantly higher with NPKM treatment being the hightest, followed by NPKF and NPKS treatments. Compared with CK, chemical fertilizer treatments resulted in increase of contents and storage capacities of nutrient. 5. The experiment of using wet sieving to obtain soil water-stable aggregates indicated that long-term fertilizer application had significant influence on aggregate size distribution and aggregate stability. The groups of >2mm and 0.25-2mm aggregates increased greatly in size and responded most effectively to the long-term fertilizer applications. Compared with CK, SOC level and aggregate stability were enhanced markedly under fertilizer application treatments and the nutrient distribution pattern also changed in different size aggregates. The nutrient increase in macroaggregates contributed most significantly to the nutrient increase overall.The contents of microbial biomass C and N were found significantly higher in the macroaggregates of >2mm and 0.25-2mm sizes than in the microaggregates of 0.053-0.25mm and <0.053mm sizes. The long-term fertilizer applications helped increase the contents of microbial biomass C and N at the same level aggregate. Under all fertilized treatments, the contents of microbial biomass C and N were found highest in the NPKM treatment, followed by NPKF and NPKS treatments.The contents of SOC and SMB-C showed a positively linear relationship with the content of macroaggregates and a negative correlation relationship with the content of microaggregates. Moreover, the contents of total N and SMB-N were found a negative correlation relationship with the content of microaggregates.6. Both dry sieving method and wet sieving method were found valid in showing the change patterns of SOC contents, total N, total P, SMB-C and SMB-N in the different aggregates. Therefore, both methods were found effective in demontrating the change regularities of the soil structure and the fertility under different fertilization systems.