Consequences of Changes in Particulate Organic Carbon in Vertisols under Pasture and Cropping

Summary

This field study of two Australian Vertisols in a semiarid subtropical environment demonstrates that particulate organic carbon (POC, >53 µm) is the preferred pool of soil organic matter lost during the conversion of native pasture to cropland, accounting for approximately 70% of the total organic carbon decline in the surface layer. POC was significantly correlated with nitrogen mineralisation rates and macroaggregate water stability, suggesting its critical role in maintaining both soil fertility and physical structure. The findings indicate that pasture-based management is particularly effective at restoring POC and soil quality in these soils.

Regional applicability

The findings are specific to Australian Vertisols in semiarid subtropical conditions and may have limited direct applicability to United Kingdom soils, which are predominantly temperate and rarely Vertisolic. However, the methodology and conceptual framework—linking particulate organic carbon dynamics to nitrogen availability and aggregate stability under pasture–crop transitions—may inform soil health assessment and pasture-based regeneration strategies in UK farming systems.

Key measures

Particulate organic carbon (>53 µm fraction), total organic carbon, nitrogen mineralization, water-stable aggregate fractions (>250 µm and <50 µm size classes), soil organic carbon in 0–5 cm layer

Outcomes reported

The study quantified changes in particulate organic carbon (POC) pools in Vertisols under different cropping and pasture management histories, and related these changes to nitrogen availability and soil aggregate stability. POC was identified as the primary form of organic carbon lost under cropping and regained under pasture restoration.

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