Study on the characteristics of CO_2 and N_2O emission from different vegetable soils

To identify the characteristics and influence factors of CO2 and N2O emission from the different intensified vegetable soils,we selected four typical fields to do the experiment which include the typical open-ground vegetable field which had over 20 years history of planting vegetable crops(OV20),new developed open-ground vegetable field which had 3 years planting history of vegetable crops converted from maize(OV3),the new developed greenhouse vegetable field which was converted from a typical maize field 3 years early(GV3),and the typical local maize field(maize).The results showed that:i)The emission flux of soil CO2 was affected mainly by soil temperature described by the exponential function and soil moisture described by the logarithmic or second-degree parabola function.The average soil CO2 emission flux from maize field was(346.8±56.5) mg· m-2·h-1 through March to July during the spring cucumber growth period,while the CO2 emission flux from OV20,OV3-M,OV3,and GV3 fields were 1.38,1.21,1.39,and 1.56 times of that from maize field respectively.ii)Soil N2O emission flux was mainly controlled by fertilization activities and also influenced by the soil temperature and soil water content.The emission peak occurred five days since basal application happened when soil temperature was at 15~20℃ and the emission peak lasted 20 days.The emission peak occurred 3 days later just after topdressing and lasted one week when soil temperature was higher than 20℃.iii)The accumulated soil N2O emission flux from maize field was N(1.95±0.10) kg·hm-2 through March to July during the spring cucumber growth period,while the N2O-N emitted from OV20,GV3,and OV3 fields were about 1.67,1.95,and 1.99 times of that from maize field respectively.iv)The N2O emission factor of chemical nitrogen was at the range of 1.86%~4.71% for the different vegetable fields during the spring cucumber growth period(through March to early-August),which were higher than the IPCC default value(1%)for the cropland soil.The emission factors of different vegetable soils were OV3OV20,and it was also higher for the greenhouse vegetable soil than that for open-ground vegetable soil.The emission factor of organic nitrogen was lower as to 0.11%.