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

No-tillage (NT), minimum tillage (MT), and conventional tillage (CT) practices were continuously applied to a Hoytville silty clay loam (Mollic Ochraqualf) soil (18 years) and a Wooster silt loam (Typic Fragiudalf) soil (19 years) in Ohio. The effect of the various tillage intensities on the profile (0–30 cm) distribution of organic C, N, and P concentrations and pH was investigated. Results showed that NT resulted in significantly (P < 0.05) higher organic C and N concentrations in the 0- to 15-cm soil increment of the Hoytville soil but significantly lower concentrations in the 15- to 30-cm soil increment. For the Wooster soil, NT resulted in higher concentrations in the 0- to 7.5-cm soil increment. No significant differences were observed among tillage intensities in the 7.5- to 30-cm soil increment. Comparison of organic C concentrations in the plow layer (0–22.5 cm) of the soils at the beginning of the long-term tillage experiment and at present showed that concentrations remained constant or decreased 11% under NT in the Hoytville and Wooster soils, respectively. Present organic C concentrations in the Hoytville soil were decreased 12 to 14% by long term MT or CT while a 23 to 25% decrease was observed for the Wooster soil. Organic P concentrations under NT were significantly (P < 0.05) higher in the 0- to 7.5-cm increment of the Wooster soil and significantly lower in the 22.5- to 30-cm soil increment. Organic C/N, C/P, and N/P ratios were calculated and higher ratios were observed under NT than under MT or CT in the surface soil increments. Tillage intensity, however, had little effect on the ratios averaged over the entire profile (0–30 cm). Soil pH was 0.1 to 0.3 units lower (P < 0.05) under NT in all soil increments except in the 22.5- to 30-cm increment of the Wooster soil where no significant differences in pH were observed among the tillage intensities.