Factors controlling soil carbon levels in New Zealand grasslands: is clay content important?
2000
Percival, H.J. | Parfitt, R.L. | Scott, N.A.
Soil organic matter is a major component of biogeochemical cycles and is important in maintaining soil quality. We investigated relationships between soil organic C and various soil and site properties that may influence long-term soil C accumulation across a range of soil orders in New Zealand. We used pedon and climatic data for 167 pedons under permanent grass, and carried out regression analysis between soil C (0-200 mm) contents (t ha-1) or concentrations (g kg-1) and climatic and soil properties, namely, precipitation, temperature, and contents or concentrations of sand, silt, clay, pyrophosphate-extractable Al (Al(py), Fe oxide, and allophane. Soil clay content or concentration explained little of the variation in soil C across all soils (R2 < 0.05) and within each soil type. Likewise, mean annual precipitation and temperature explained little variation in soil C content or concentration (R2 < 0.15 for precipitation, R2 = 0.04 for temperature). Allophane content or concentration was unrelated to soil C in the soils of volcanic origin; Al(py), however, correlated strongly with both soil C content and soil C concentration across all soil types (R2 = 0.55 and 0.60, respectively). When all factors were combined in a multiple regression analysis, the combination of Al(py) and allophane contents explained the greatest amount of variation in soil C content (R2 = 0.57), whereas the combination of Al(py), Fe oxide, allophane, and clay concentrations explained the greatest amount of variation in soil C concentration (R2 = 0.67). Our results suggest that in New Zealand soils, chemical stabilization of organic matter is the key process controlling soil C accumulation, and that clay content relates poorly to long-term soil organic C accumulation.
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