Macroaggregation is promoted more effectively by organic than inorganic fertilizers in farmland ecosystems of China—A meta-analysis

Fertilizers can affect formation, size distribution and stability of soil aggregates in agricultural ecosystems. Although many independent studies have been recently carried out to understand the effects of fertilizers on soil aggregates in farmland ecosystems of China, the results remain widely contradictory. A meta-analysis was conducted using a total number of 1286 observations from 100 publications between 2005 and 2020 to quantitatively analyze the effects of different fertilizer treatments, duration of fertilizer application, regional heterogeneity, soil texture, and aeration conditions on the composition of soil aggregates. Results showed that long-term annual single application of organic fertilizer, inorganic fertilizer (N and NPK) and combined application of organic and inorganic fertilizers increased the proportion of > 2 mm fractions, but decreased the proportion of 0.25–0.053 mm and < 0.053 mm fractions, respectively. The promotion of macroaggregates (> 0.25 mm) by long-term application of organic fertilizer and the combined application of organic and inorganic fertilizers were significantly stronger than inorganic fertilizer, but the opposite for microaggregate (< 0.25 mm). The application of organic and inorganic fertilizer and straw return should be applied in sandy loam and silty loam, and clay loam was applied mainly manure (M), nitrogen plus manure (NM), nitrogen, phosphorus and potassium plus manure (NPKM) and nitrogen, phosphorus and potassium plus straw return (NPKS), while reducing the single application of inorganic nitrogen (N). Inorganic fertilizers and combined with organic-inorganic fertilizer increased the proportion of > 2 mm fractions in anaerobic soil significantly more than that in well-aerated soil. Long-term annual single application of N and M promoted the proportion of > 2 mm and 2–0.25 mm fractions significantly more than that of combined application of nitrogen and phosphorus and potassium (NPK), NM, NPKM and NPKS in experiments conducted in the Northeast of China. In addition, our results also showed that the proportion of macroaggregates did not increase linearly with continuous fertilizer input, but with the extension of fertilization durations, the macroaggregates transformed to microaggregates gradually after reaching the saturation state. Organic fertilizer and organic-inorganic combined application had longer time to promote macroaggregates than inorganic fertilizer.