Organic Carbon, Nitrogen, and Phosphorus Concentrations and pH in Soil Profiles as Affected by Tillage Intensity

Summary

This long-term field experiment (18–19 years) compared no-tillage, minimum tillage, and conventional tillage on two Ohio soils, measuring how tillage intensity affected vertical distribution of organic carbon, nitrogen, phosphorus and soil pH. No-tillage maintained higher carbon and nitrogen in surface layers but showed stratification with lower concentrations at depth, whilst conventional and minimum tillage reduced organic carbon stocks by 12–25% over the experimental period. Soil pH was marginally lower under no-tillage in most increments, and organic matter stoichiometric ratios (C/N, C/P, N/P) differed among tillage types in surface soil but converged when averaged across the full profile.

Regional applicability

This United States-based study on Midwestern clay loam and silt loam soils is directly applicable to similar soil types and arable systems in the United Kingdom, particularly in regions with comparable soil genesis and temperate crop production. The long-term nature of the experiment (18–19 years) provides robust evidence relevant to UK policy on conservation agriculture adoption and soil carbon targets, though local soil type variation and climate would require field validation.

Key measures

Organic carbon, nitrogen, phosphorus concentrations and pH at multiple soil depths (0–7.5 cm, 0–15 cm, 7.5–30 cm, 15–30 cm, 22.5–30 cm increments); organic C/N, C/P, and N/P ratios; percentage change in organic C from baseline over 18–19 years

Outcomes reported

The study measured organic carbon, nitrogen, and phosphorus concentrations and pH across soil profiles (0–30 cm) under three contrasting tillage regimes applied for 18–19 years continuously on two soil types in Ohio. No-tillage resulted in significantly higher organic C and N in surface increments but lower concentrations at depth, with reduced organic C loss compared to conventional and minimum tillage over the long-term study period.

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