Effect Of Biochar Amendment On Acid Soil In North China

Since1980s, large amount of nitrogen fertilizer was used in order to increase crop yields to fulfill the people’s demands. Due to long-term excessive N fertilizer application, unreasonable farming system and management measures, the soil acidification in north China was getting more severely. In recent years, the rise of biochar technology provided a new environmental protection, high efficiency way for ameliorating soil acidification. Based on the soil acidification caused by excessive nitrogen fertilizer used, biochars were prepared from cotton straw and peanut hull at different pyrolysis times and temperatures, then two peanut hull biochars were selected for soil incubation and changes of physical and chemical properties of acid soil were studied with biochar amendment at ratio of2.5%and5%, separately. Through the effect of biochar on soil N transform, the mechanism of biochar amendment on acid soil was explained. Moreover, the rhizosphere effect and N utilization was studied with biochar amendment, and the economic benefit of biochar reducing fertilizer applied was analyzed and estimated. The main conclusions are as follows:(1) The typical agricultural residues in north China-cotton stalk and peanut hull were selected, and pyrolized to prepare biochar. Within2hours, the physical and chemical properties of biochars changed significantly as the pyrolysis time extended, but began to flatten when the pyrolysis time was above2hours. The biochar yield and cation exchange capacity decreased as the pyrolysis temperature rised, while the ash content, pH, surface area and the content of K, Ca, Mg increased.(2) The pH of peanut hull biochar was alkaline when pyrolysis temperature was above300℃, but the CEC was only2.86cmol kg-1which was not suitable for acid soil amendment when pyrolysis temperature was above400℃. Therefore, two biochars (H300, H400) which was obtained from300℃and400℃was selected for acid soil amendment. (3) When H300and H400were added into the acid soil at ratio of2.5%, the soil bulk density decreased by5.1%and7.1%, while the pH increased by0.58and0.80units as well as organic matters and CEC elevated by65%,35%and5.5%,9.0%, separately. The improvement of soil physicochemical properties was much more significant when the ratio of biochar was5%.(4) H300and H400could strongly absorb NH4+, and H400adsorption ability was obviously higher than that of the H300when the concentration of NH4+was above10mg L-1. However, NO3-was barely absorbed on H300and H400.(5) Through the absorption NH1+in one hand, and the amount of ammonia oxidizing bacteria decreased by H300and H400in the other hand,the nitrification was strongly inhibited. Just because of this, soil pH was arised and nitrogen was maintained.(6) The growth of maize plant was significantly promoted with two biochars amendment. The maize biomass was improved by30.3%and32.7%when H400was added into acid soil at ratio of2.5%and5%. Meanwhile, the root morphology was enhanced.(7) A small amount of nitrogen that could be neglected was released from H300and H400, but the N utilization efficiency was significantly improved with biochar amendment. The amount of nitrogen fertilizer decreased by8.5%,13.5%,27.0%and27.7%when H300and H400was used at the ratio of2.5%and5%.