The Effects Of Biochar On Nutrients Leaching From Slurry Applied Into Soils

Two experiments, soil column experiment and pot experiment, were carried out to study the effects of biochar on nutrients leaching from slurry applied into soils, under different environmental temperatures. Soil column experiment included three slurry application rates, Oml (Control),40ml and80ml; three biochar application rates,0%(Control),2%and4%; two temperature rates,20℃and30℃. The largest slurry application rate was calculated according to the annual rainfall in Chongqing. The slurry was applied into soil column five times. The contents of nutrients in leaching solution were estimated, including total and available potassium, total and available phosphorus, total nitrogen, NH4-N and NO3-N, electrical conductivity. The pot experiment was conducted to estimate the effects of slurry application on tillering, above/underground biomass and their ratio, nutrients uptake of Lolium multiflorum Lam, and soil chemical and enzyme activities. There were four slurry application rates,0(Control),667,867, and1133ml·kg-1soil. The main results are as fallowings:1. Soil column experimentThe contents of available potassium. total phosphorus, available phosphorous and electrical conductivity in leachate increased significantly with increasing biochar application rates (P<0.05). The contents of total nitrogen and.NH4-N showed no significant changes with increasing biochar rates. The leaching of soil NO3-N was significantly influenced by biochar application. When there was no slurry applied, the contents of NO3-N in leachate decreased significantly with increasing biochar rates under conditions of two temperatures (P<0.05).The contents of available potassium, total phosphorus, available phosphorous, total nitrogen, NH4-N, and electrical conductivity in leachate increased significantly with increasing slurry application rates (P<0.05). The contents of NO3-N changed insignificantly with increasing slurry application rates.Overall,the content of NO3-N with40ml slurry was larger than that with80ml slurry, followed by Oml slurry.The contents of available potassium,total phosphorus, available phosphorous.total nitrogen. NO3-N, and electrical conductivity in leachate at30℃were significantly higher than those at20℃. No significant change was found for content of NH4-N in leachate between two temperatures. Overall, the absorption performance of biochar on nutrients was larger when more slurry was applied into soils. Under lower slurry application rate, the nutrient contents in biochar itself influenced the nutrients in leachate more.2. Pot experimentWhen the plants were applied with slurry of667ml·kg-1soil, tiller number and aboveground biomass of L. multiflorum increased about140%, underground biomass decreased, resulting in a decrease of ratio of under/aboveground biomass. The concentrations of plant nitrogen, phosphorus and potassium increased250%,16%and50%, respectively. No further increase of tiller number, biomass, and nutrients uptake were observed with further increasing slurry application rates. However, the contents of soil total nitrogen, total phosphorus and total organic carbon, and electric conductance increased with increasing slurry application rates, resulting in enrichment in soil. Soil pH decreased with increasing slurry application rates. Slurry application increased soil urease activity but decreased soil dehydrogenase activity. Overall, L.multiflorum could tolerate excess amount of slurry to some extent. It was suggested that slurry application rate of667ml·kg-1soil was suitable for the growth of L. multiflorum and relatively safe for environment.