Fertilizer impacts on soil aggregation and aggregate-associated organic components

A 5-year (2012–2016) field experiment was conducted to investigate the impacts of different fertilizer treatments (no fertilizer, mineral and organic fertilizer) on organic carbon and soil water-stable aggregates in a North China Plain Vertisol. Compared with no fertilizer (control), single mineral fertilizer did not significantly (P < 0.01) affect organic carbon content or aggregate mass proportion in bulk soil. Small and large macroaggregate mass proportions increased, but applying organic manure significantly decreased the silt + clay fraction and microaggregates. Organic manure amendment significantly enhanced organic carbon concentrations in aggregates (large macroaggregates, > 2000 μm; small macroaggregates, 2000–250 μm; microaggregates, 53–250 μm; and free silt + clay fraction, < 53 μm) and aggregate subfractions, including intraparticulate organic matter and silt + clay subfractions (< 53 μm). Single mineral fertilizer amendment increased organic carbon concentrations in macroaggregates, particularly intraparticulate organic matter. The results indicated that the organic carbon increase in organic manure-amended soil were possibly due to enhanced silt + clay subfractions, which then promoted macroaggregates formation. Applying organic manure could improve organic carbon sequestration and maintain its stability in aggregates, whereas mineral fertilizer only enhanced organic carbon in large macroaggregates, but with low stability.