Effects Of Biological Carbon On Soil N ₂ O Emissions From Degraded Vegetable

The area devoted to greenhouse vegetable crops in China accounts for 14.5% of the total cropland, and went through a change from 3.3 million ha in 1976 to 24.8 million ha in 2011. High amounts of nitrogen fertilizer was applied to greenhouse vegetable filed to get high yield and economic benefit in recent years. There was serious accumulation of nitrate in topsoil due to large of nitrogen fertilizer application along with the increasing length of planting, whereas negative environmental problems appeared, such as soil acidification and soil salinization, the occurrence of soil-borne disease, successive cropping obstacle and crop production reduction, which leaded to unsustainable development in soil finally. As we all known, N2O played an important role in soil nitrogen cycle, mainly from nitrification and denitrification. The application of nitrogen fertilizer and accumulation of nitrate in topsoil of greenhouse vegetable soils provided enough substrate for nitrification and denitrification. Many researches showed that N2O emission in vegetable soils was significant higer than other agricultural soil and was the the main source of N2O. Furthermore, the reductive soil disinfestation (RSD) method of adding organic material into soil under flooding condition was applied to remediate degraded vegetable soil, which was effective in reducing soil nitrate, in removing soil acidification and soil salinization. However, there was more N2O emission in this soil remediation because denitrication was promoted. Therefore, it is necessary for taking effective steps in reducing soil nitrate and N2O emission in remediation of degraded intensive vegetable fields, and the results will benefit for control N2O emission in agricultural soil. Bichar has strong pore structure, large surface area, strong absorption ability, high pH value and organic matter, and can also stable in soil. In recent years, there were many researches showed that biochar could affect soil nitrification and denitrification, and then had influence on N2O emission. At present, there was controversy in the influence of biochar on N2O emission, and the mechanism was unclear as well.Therefore, our experiments studied degraded greenhouse vegetable soil with or without biochar, and also adding calcium oxide into soil, the aims were to detect N2O emission and the change of denitrying microorganisms in different treatments. In addition, we studied the influence of biochar amended on N2O emission in degraded vegetable soil and in remediation of degraded vegetable soil, and explained its mechanism. Furthermore, we planted tomato in degraded vegetable soil with or wihout remediation with biochar or calcium oxide for comparing N2O emission and plant growth in these soils. The main results was as follows:The results on two typical degraded greenhouse vegetable soil in Wujiang and Nanjing Qilinmeng indicated that the application of 5% biochar (w/w) and 2 mg g-1 calcium oxide significantly reduced N2O emission, and the former was better than the latter.The results of microcosm and greenhouse experiments both showed that the application of 3% biochar and 1 mg g-1 calcium oxide significantly reduced N2O emitted from degraded vegetable soil,40.70%,17.35%, respectively. Soil pH was an important factor in reducing N2O emission. In addition, the role of biochar had better effect. The results of denitrifying functional microbial showed that the application of biochar significantly affect the abundance of nirK、nirS、norB and nosZ genes. Person correlation analysis showed that N2O production rate was positively correlated with the abundance of nirK, norB gene and negetatively correlated with the abundance of nirS gene. And regression analysis showed that norB gene played the most important role in N2O emission in soil remediation.The greenhouse experiment on process of tomato planting in soil with or without remediation studied the influence of biochar and calcium oxide amended on N2O emission. The result showed that N2O emission was significant higer with biochar and calcium oxide amendment after soil remediation. The possible explaination was that biochar and calcium increased soil pH and promoted nitrification and denitrification, which resulted in more N2O emission. Compared with the soil without remediation, biochar and calcium oxide amended in soil improved soil total organic carbon and total nitrogen, promoted the growth of planting, significantly increased crop yield and biomass overground. The net nitrification rate of nitrogen in remediated soil was higher than unremediated soil, biochar and calcium oxide amendment was much higher after tomato were harvested. However, biochar amended in soil can reduce by 39% N2O emission in the whole process, including the process soil remediation and crop planting after remediation.