Abstract
Core IdeasThe optimal N rate was about 100 kg ha−1yr−1.Best duration for fertilization is less than 10 yr.The application of NPKM demonstrates the greatest potential for increasing microbial biomass in China's cropland.Soil microbial biomass (SMB) plays an important role in enhancing soil aggregation, promoting nutrient cycling, and making a substantial contribution to soil organic matter. Little is known about the underlying mechanism and broad‐scale responses of SMB to long‐term fertilization practices on a regional scale. The objective of this study is to characterize changes in SMB of predominant cropping systems in China (mainly producing maize [Zea maysL.], wheat [Triticum aestivumL.], rice [Oryza sativaL.], and soybean [Glycine maxL.]) under different fertilization regimes using meta‐analysis. We integrated data from more than 60 studies conducted in China from 1990 to 2015 and found that application of inorganic fertilizer, straw, straw with inorganic fertilizer, manure, and manure with inorganic fertilizer increased soil microbial biomass carbon (Cmic) concentration, while nitrogen‐only (N) and nitrogen plus manure (NM) decreased soil microbial biomass nitrogen (Nmic) concentration compared with control (no fertilizer application). Our results indicated greater Cmicand Nmicresponses to inorganic N, P, and K‐based fertilizers plus manure (NPKM) in the mid‐latitude region compared with those in the low‐ and high‐latitude regions of China. The differences in means (Cmicor Nmicconcentration) among different fertilization treatments decreased with experimental duration, and Nmicconcentration decreased with increase in N rate. Our results suggested that long‐term (∼10 yr) continuous annual fertilization of N provided the greatest SMB, and the optimal rate was about 100 kg N ha−1yr−1. The application of NPKM demonstrated the greatest potential for increasing SMB of major cropping systems in China.
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