Soil organic carbon pools under long-term mineral and organic amendments: a multisite study

Abstract

Abstract Soil organic carbon (SOC) has various pools with different stabilization mechanisms. It is unclear how these SOC pools respond to various mineral and organic amendments depending on a large climate-soil gradient. Here, we studied in three zonal soils: Ferralic Cambisol (subtropic), Calcaric Cambisol (warm-temperate) and Luvic Phaeozem (mid-temperate) under 23-year mineral, straw and manure amendments. Six SOC sub-pools were isolated: unprotected, physically, chemically, biochemically, physico-chemically and physico-biochemically protected pools. Compared to initial level, SOC and most sub-pools increased in the three soils under manure application (p < 0.05), but little under straw and mineral amendments. The Luvic Phaeozems had much higher sequestration efficiencies of bulk SOC (27%) and its five sub-pools (5–7%) more than the Calcaric Cambisol (9%, 1–2%) and Ferralic Cambisol (9%, 0.5–1%). In contrast, Ferralic Cambisol had highest sequestration efficiency of unprotected pool (7%). The Calcaric Cambisol had divergent patterns of the six SOC pools compared with Luvic Phaeozems and Ferralic Cambisol, due to the low clay content. With the build-up of bulk SOC, the building-up abilities of non-protected, physically-, chemically- and biochemically-protected pools depended on soil type, while the building-up abilities of physico-chemically- and physico-biochemically-protected pools were convergent (12–19%) among soils. In conclusion, the Luvic Phaeozems had much higher build-up ability of bulk SOC and most sub-pools than the other two soils. With the build-up of SOC, the physico-chemically- and physico-biochemically-protected pools (most stable) had convergent response rates among soils, while the other pools had divergent response rates. Graphical Abstract

Keywords

• Manure amendment
• Microaggregate
• Particulate organic matter
• Soil aggregation
• Soil C sequestration
• Soil organic matter