The Response And Mechanism Analysis Of Soil Ecosystem To Typical Organic Fertilizers

The increasing demand for food intensive farming leads to soil infertility, in order to improve soil fertility, organic fertilizers are widely used all over the world. However, organic fertilizers may have effects on levels of soil carbon and nitrogen, the global soil microorganism, emissions of greenhouse gases in agricultural systems. In this study, typical organic fertilizers including pig manure compost (PMC), sludge manure compost (SMC) and cake manure (CM) were selected as research objects, while both inorganic fertilizer (IF) and control treatment (CK) were as the contrasts. A pot experiment in a greenhouse was carried out to analyze soil carbon and nitrogen pool; to discuss the effects of organic fertilizers on soil microbial activity, functional diversity, the diversity of bacterial community structure, and CO2and CH4fluxes from the plant-soil systems. The responses of soil ecosystems to different organic fertilizers could provide theoretical basis for the application of organic fertilizer in agricultural production. The main findings are as following:1. Both PMC and SMC didn’t show plant toxicity through Brassica Chinensis and Lolium perenne L. seed germination test, and they both increased the biomass of Brassica Chinensis. Cake manure showed obvious plant toxicity on Brassica Chinensis and Lolium perenne L, resulting in the lower biomass of Brassica Chinensis comparing with those for the unfertilized treatment.In the study, SMC did not change the pH values comparing with those for CK, while PMC, CM and IF exhibited acidification phenomenon, which all decreased pH gradually. The pH values of CM and IF both began to be stable after25days; the pH value of PMC dropped until the25th day and then rose at6.41at the end of the trial. All the fertilized treatments can improve the value of soil EC values following the order IF>PMC>SMC>CM.2. Soil total carbon (TC) and soil organic carbon (SOC) content for all fertilized treatments, which followed the order PMC≈SMC>CM>IF>CK. The organic fertilizers can cause the soil dissolved organic carbon (DOC) to increase initially and then to decrease after about13days. On the day35, DOC of CM, SMC and PMC treatments was still7.06,5.19and5.08times than the initials respectively; Meanwhile CM entered into the next equilibrium after27days. It supposed that additional organic matter or the increase of soil microbial biomass could result in the enhancement of soil organic carbon.3. The average levels of total nitrogen (TN) for treatments followed the order CM>IF>PMC>SMC>CK, which all fluctuated up and down over the study. And total dissolved nitrogen (TDN) levels also the same order as TN for all treatments, among which both CK and SMC slowly declined, PMC began to decline after day20th, both CM and IF increased sharply after equilibrium periods of13and11days respectively following by decreases since day30. Ammonia-N (NH4+-N) for fertilized treatments all declined gradually and arrived at the level of CK; nitrate-N (NO3-N) for all treatments displayed fluctuations in the study. Dissolved organic nitrogen (DOC) for all treatments kept the similar trends with TDN. These showed both IF and CM could release dissolved nitrogen in a short period, while composts were longer.4. Microbial biomass carbon (MBC) for fertilized treatments all exceeded the level of that for CK; meanwhile microbial biomass nitrogen (MBN) all displayed fluctuations over the study. Basal respiration (BR) rates for fertilized treatments have no obvious differences, which followed the processes of increase, decrease and then tend to be stable, and were all still higher than the initials. The metabolic quotients (qCO2) for all treatments experienced twice declines, among which were no obvious different. These results showed that soil microbial biomass and microbial activity could be enchanced by organic fertilizers, and they tend to be stable and regress.The effects of organic fertilizers on the metabolic diversity of microbial communities were assessed by Eco-Biolog plate. The values of the average well cell development (AWCD) were stimulated during incubations for organic fertilizer treatments, among which the differences were diminished gradually and tend to clear away. The diversity of CLPP was evaluated by Shannon index, McIntosh index and Simpson index. Shannon index for all treatments followed the order SMC>PMC>CM>CK>IF on the day35th, and CM>PMC>SMC>CK>IF on the day75th. These results indicated organic fertilizers enhanced the microbial metabolic diversity, while inorganic fertilizer not only decreased the metabolic potential, the potential metabolic diversity was also be depressed. Principal component analysis (PCA) distinguished the microbial communities for PMC and CM had the similar metabolic diversity, and the same to IF and CK at the end of the study.5. Both organic and inorganic fertilizers can both increase bacterial community structure richness in soil, but at the same time reduce homogeneous degree. The number of restriction fragments in organic fertilizer treatment was larger than that of IF and no fertilizer treatments. In the1st day, bacterial community structure of the PMC and SMC are similar; the difference between PMC and sewage SMC treatments increased on the35th day; and after75days, the PMC is similar to CM, and the gap between IF and CK narrowed. Principal component analysis suggested both bacterial function diversities and bacterial communities were influenced by pig manure compost and cake manure applications.The effects of organic fertilizers on bacterial community structures were investigated using terminal restriction fragment length polymorphism (T-RFLP) analysis. The same terminal restriction fragment (T-RFs) were enhanced among fertilizerd treatments in the beginning, and then declined to the initial status. Specific T-RF was happened for different fertilized treatments. The diversity of bacterial community was evaluated based on dominant T-RFs. Both Shannon index and richness index for organic fertilized treatments were all higher than those for CK. The diversity index for CM were highest among all treatments at the begining, meanwhile SMC grew and began to be the largest at the end of the study. The results showed that organic fertilizers could stimulate the diversity of bacterial community. The T-RFLPs profiles of bacterial communities for treatments were compared by principle component analysis (PCA). The results suggested pH value for soil must be an important factor affecting the bacterial community structures.6. Gas samples for the plant-soil ecosystems were collected using a static chamber approach, and the concentrations of CO2and CH4were determined using gas chromatography. The results showed that CO2was fixed by the plant-soil ecosystem during Brassica chinensis growth after fertilisation and that the CO2and CH4fluxes were not significantly different among the treatments compared with CK. The ecosystem uptake of CO2increased with the soil temperature and the variation was in agreement with a first-order exponential curve. The plant-soil ecosystems were minor CH4sinks and sources, especially CH4sink, for all of the treatments. The results indicate that a plant-soil ecosystem could be a carbon sink, and that fertiliser application had no significant effects on either the CO2or the CH4uptake in a plant-soil ecosystem.