Meta-analysis of the spatial distribution of denitrification intensity in the vadose zone

In this paper, the denitrification intensity data of 197 groups are screened out according to 3955 papers on the vadose zones published from 1970 to 2017. Based on the meta-analysis, the spatial distribution of denitrification intensity in typical ecological types (horizontal) and different sampling depths (vertical) is studied emphatically, the main factors of denitrification intensity in the vadose zone are analyzed and their function relations are studied. The regression function is used to obtain the denitrification intensity relation of the vadose zone. The results show that in the horizontal direction, the distribution characteristics of denitrification intensity of 0~0.5 m in the vadose zone are significant, which are sorted from big to small as follows: forest (8.03±0.21 mg/(kg·d)), farmland (3.54±0.08 mg/(kg·d)), grassland (3.38±0.12 mg/(kg·d)), wetland (2.32±0.23 mg/(kg·d)), and desert (2.15±0.56 mg/(kg·d)). In the vertical direction (within 6 m), the denitrification intensity of each ecological type is of the "S" type with the increasing depth. There are some differences in the main controlling factors of the denitrification intensity in the vadose zone under different ecological types and sampling depths, including clay, organic matter, total nitrogen, nitrate nitrogen and available phosphorus. The regression equation between the denitrification intensity and the main controlling factors in the vadose zone is given.