Macroaggregate-associated physical and chemical properties of a no-tillage chronosequence in a Miamian soil

Ochoa, C. G., Shukla, M. K. and Lal, R. 2009. Macroaggregate-associated physical and chemical properties of a no-tillage chronosequence in a Miamian soil. Can. J. Soil Sci. 89: 319-329. No-tillage (NT) has been shown to increase macroaggregate stability and soil organic carbon (SOC). Our objective was to quantify the effects of NT duration and slope position on macroaggregate-associated bulk density (rho(b)), available water content (AWC), hydrolysable and nonhydrolysable OC concentrations in fields under corn rotation. All fields were on Oxyaquic Hapludalfs (Alfisols) classified as Miamian soil. Macroaggregates (5-8 mm diameter) were separated from triplicate soil samples collected from 0-10 and 10-20 cm depths of the summit slope (SS) and toe slope (TS) positions from four fields under NT for the past 15 yr (NT15), 10 yr (NT10), 6 yr (NT6) and also from a chisel-tilled field (NT0) to a depth of 20 cm. At the SS position, macroaggregate-associated hydrolysable and nonhydrolysable OC were greater for NT 15 than NT6 in both depths. At the TS position, hydrolysable OC was greater for NT10 than NT6 in the 0-10 cm depth only. Macroaggregate-associated AWC and hydrolysable OC were positively related to the NT duration, especially at the SS position. A positive correlation was obtained between water-stable macroaggregates (WSA) and hydrolysable OC at both depths and slope positions. A negative correlation between WSA and nonhydrolysable OC was observed at SS and TS positions in the 0-10 cm depth only. The increase in aggregate-associated hydrolysable OC at the SS position of fields under NT for 15 yr indicates that C accretion in macroaggregates is likely dependent on the continuation of NT.