Fertilization impacts on soil microbial communities and enzyme activities across China’s croplands: a meta-analysis

Objectives  Fertilization directly or indirectly changes the balance of nutrients in agricultural ecosystems, thereby affecting soil physical, chemical and biological properties. It is necessary to explore the effects of fertilization on soil biological characteristics under different cropping systems and soil conditions, so as to devise optimal strategies for rational fertilization and soil fertility improvement.

Methods  By collecting data from published literature in the last 10 years (2008–2018), a database containing 185 groups of microbial biomass and community structure was established. A meta-analysis was used to quantify the effects of fertilization on soil microbial biomass, community structure and enzyme activities.

Results  Compared with the unfertilized control, fertilizer application significantly increased the soil phospholipid fatty acids (PLFA) and microbial biomass carbon and nitrogen contents by 28.5%, 30.9% and 41.6%, respectively. Relative to the control, organic fertilizer application increased soil total PLFA and microbial biomass carbon and nitrogen contents by 47.3%, 50.4% and 58.7%, respectively, equivalent to 1.8, 1.4 and 2.9 times higher than those of the mineral fertilizer treatments correspondingly. Compared with the control, fertilization increased the PLFA contents of various microbial communities, with bacteria, fungi and actinomycetes increased by 23.8% to 30.4%, and Gram-negative bacteria (G^–) and Gram-positive bacteria (G⁺) increased by 37.8% to 43.2%. Organic fertilizer application significantly increased the PLFA contents of all types of bacteria relative to mineral fertilization. Mineral fertilization increased total PLFA contents by 17.9% in double-cropping system, and 18.3%−27.6% in paddy or upland-paddy. However, mineral fertilization had little effect on soil microbial biomass under mono-cropping or upland. The magnitude of increased soil microbial total PLFA contents was significantly higher in soils subjected to organic fertilizer application as compared to mineral fertilization in soils with various pH. The application of mineral fertilization in soils with pH < 6 and pH > 8 had no effect on soil microbial total PLFA contents. Compared with the control, fertilization significantly increased the activities of β-glucosidase (42.4%) and N-acetyl-glucosaminidase (174.5%) involved in soil organic matter decomposition, but did not for the activity of leucine aminopeptidase related to nitrogen cycle. Statistical analysis also showed that different fertilization did not change the fungi/bacteria (F∶B) and the Gram-positive bacteria/Gram-negative bacteria(G⁺∶G^–) of the soil microorganisms.

Conclusions  Fertilization changed soil microbial biomass and enzyme activities associated with decomposition of organic matter under different cropping systems, land-use types and soil pH gradients, but did not change the fungi/bacteria (F∶B) and the Gram-positive bacteria/Gram-negative bacteria (G⁺∶G^–) of the soil microorganisms. Organic material application (alone or combined with mineral fertilizers) is conducive to improving soil microbial activity and diversity in farmland, the effect is significantly better than that of single application of mineral fertilizer.