Abstract:

[Objective] This study aimed to reveal the effects of alfalfa cultivating on soil available nitrogen content in different land uses and to assess the driven factors. [Method] A total of 28 published papers indexed in the database of China National Knowledge Infrastructure （CNKI） were collected, and these papers included 31 groups of soil available nitrogen content data of alfalfa cultivating lands. With clear tillage as the control, the effects of alfalfa cultivating on the soil available nitrogen content of such land uses as pasture land, forest land, farmland, desert land and orchard land were assessed by using Meta-analysis. Furthermore, the mixed effect model was used to clarify the driven factors that contributed to the impacts of the meteorological factors as well as the soil physical and chemical properties on the mean effect size of soil available nitrogen content. [Result] Alfalfa cultivating extremely significantly （P<0.001） increased the soil available nitrogen content, and the mean effect size and increase range were 0.27±0.07 and 30.99%, respectively. The increase range of soil available nitrogen content for different land uses attributed to alfalfa cultivating from high to low was pasture land （P<0.001）, forest land （P<0.001）, farmland, desert land （P<0.001） and orchard land, which were 60.01%, 58.41%, 32.31%, 27.12% and 22.14%, respectively. The mean effect size of pasture land and forest land was significantly （P<0.05） higher than that of farmland, desert land and orchard land. The mixed effect model-based analysis demonstrated that the soil moisture and available potassium content had significant （P<0.05） effects on the mean effect size, which could explain 47.81% and 17.46% of the effect size variation, respectively. [Conclusion] The effects of alfalfa cultivating on soil available nitrogen content in different land uses exhibit a strong heterogeneity. Increasing soil moisture and available potassium content will help to enhance the nitrogen fixation capacity of alfalfa.

Key words: alfalfa, soil available nitrogen, mean effect size, structural equation model