| Nitrous oxide（N2O）is an important greenhouse gas,and it can result in greenhouse effect and destruct ozone layer.The N2O concentration in the atmosphere increased year by year.It had been reported that farmland ecosystem was the main source of N2O,and crops growth would effect the soil N2O emission.Leguminous crops can fix nitrogen from atmosphere by root nodule bacteria nitrogen fixing system,and its rhizosphere environment is different from non-leguminous crops,it had different effect on soil N2O emission.The pot experiment was conducted to plant soybean（Glycine mas）,maize（Zea mays）and sorghum（Sorghum bicolor）.The soil N2O emissions was sampled by static closed chamber method and analyzed by gas chromatography,then analyse the soil N2O emission flux,total emissions,emission factor during crops growing and root rot period from different treatments.The purpose of experiments was providing the measures of controlling N2O emission from farmland ecosystem and a scientific basis for reasonable application of nitrogen fertilizer.The main results were as follows:1.From the seasonal variation of N2O emission flux,the results showed that the emission peak main occurs in 35 days after sowing.Except LNS,all treatments have not produced much N2O until the crops were harvest,the emission flux range small and kept at a lower level.The emission flux of LNS still at high level still harvest.In the 35 days after sowing,the tatal N2O emission of LNB、HNB、HNS and HNM account for 78.5%～93.3%,and HNK accounted for 85.4%in 15 days after sowing.The temperature had no significant effects on soil N2O emission flux,it had been influenced by crops growth and N fertilizer application.2.The results showed that both crop growth and fertilization significantly influenced the soil total N2O emission during the period of crops growing,it ranking as following:HNS>HNB>HNM>HNK>LNB>LNS.Except HNS,crops growing can reduce the N2O emission.The soil which with high nitrogen level contributed more N2O than the soil with low nitrogen level,it can say that nitrogen fertilization significantly increased total N2O emission.3.There is significant difference between treatments on N2O emission factor,it affected by the level of nitrogen fertilizer and crop types,it ranking as following:HNS（4.54%）>HNB（2.08%）>HNM（1.71%）>LNS（1.43%）>HNK（1.27%）>LNS（0.55%）.It was concluded that crop species and nitrogen level had different effects on soil N2O emission factor.4.After the crops harvested,soil N2O emission have significantly differences between all treatments in the root rot period it ranking as following:HNS>LNS>HNM>HNK>LNB =HNB,crops root rot can increase the soil N2O emission,legumes crops rot can make soil emission more N2O and bare soil on different nitrogen level had no significant differences.It was concluded that crop root species and nitrogen level had significant effects on soil N2O emission.Crops growth and nitrogen fertilization application level would effect soil N2O emission.The N2O emission from soil under soybean growth was different from the soil under maize and sorghum growth,because soybean can acquired N by symbiotic nitrogen fixation system so there was significant different on soil N2O emission,the nitrogen content in the fertilizer also effect the soil N2O emission. |
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