Effects Of Exogenous Citric On Soil Nutrients And Enzyme Activities And Microbialactivity Of Old Manured Loessal Soil

Plant restoration and reconstruction are fundamental to Ecological Restoration conservation of Loess Plateau, the litter and root secretion of vegetation can regulate and ameliorate the soil physical and chemical properties and microbial environment, thereinto, low molecular weight acids in the rhizosphere play an important role in soil remediation. At present, the study on action mechanism between low molecular weight acid and soil are rare. Using Old Manured Loessal Soil as test sample, this research investigated the effects of exogenous citric acid on soil nutrients, soil enzyme activities and microbialactivity with adding citric acid to the soil. The main results are as follows:1. The losses of the contents of total N was generally decreased with the increasing concentration of citric acid, as time passing by, the gaps between high and low concentration of citric acid treatment were enlarged. The contents of alkali hydrolyzable nitrogen and NO3-N decreased with experimental time and the increasing citric concentration. Excluding the control, soil total P increased slightly on the 30th day, after 30 days the changes were not distinct. The contents of available phosphorus of the control changed not obviously, while the others decreased with time and the increasing citric acid concentration.2. Soil pH value increased with the increase citric concentration, at the earlier stage soil pH value rose gradually over time, and then became smooth and steady at the later stage. Soil EC decreased gradually with time and the increasing citric concentration。3. In the same period, soil organic carbon increased with the increasing citric acid concentration. As the time went by, soil organic carbon content for low concentration treatments (the control, treatment 1, treatment 2) decreased, content of organic carbon for high concentrations treatments (treatment 3, treatment 4, treatment 5) increased gradually and then became steady; soil C/N increased at the earlier stage, at the later stage the change was not significantly, but the gap between different treatments gradually expanded. Soil microbial biomass carbon increased generally with the increasing citric concentration, while decreased slightly with experimental time and became steady at the later stage.4. Soil catalase activity increased generally over time;urease activity decreased over time considerably;invertase activity did not show apparent regularity;alkaline phosphatase activities increased with the increasing citric concentration.5. Using the mathod of principal component analysis, 14 soil fertility indexes were reclassified and simplified. It was found that: the first principal component was the measurement of the transformation of soil N, P and organic matter to the microorganisms organic form, reflected the fixation and reservation of organic carbon, nitrogen, phosphorus by soil microorganisms. The second principal component reflected the smart different influences of different citric concentrations in on soil fertility conditions. For the treatment 3, soil fertility indexes were more sensitive to the influence of citric acid.