POTENTIAL SOIL RESPIRATION AND RELATIONSHIP TO SOIL PROPERTIES IN RIDGE-TILLAGE

Differences in traffic and tillage intensity among positions in ridge tillage create distinctly different environments for microbial activit y. This study was conducted to assess the impact of long-term controll ed wheel traffic on soil respiration in ridge-till and to use correlat ion analysis to identify relationships between soil respiration and so il physical and chemical properties. Soil respiration was evaluated fr om 0 to 30 cm in one row, one tractor-trafficked interrow, and one non trafficked interrow of continuous corn (Zea mays L.) and continuous so ybean [Glycine max (L.) Merr.]. Soil respiration was measured on distu rbed samples at three levels of water-filled pore space (WFPS) by gas chromatography for 25 d. Properties assessed included bulk density, so il strength, texture, aggregate-size distribution, saturated hydraulic conductivity (K-sat), water retention characteristics, organic C, and total N. Soil respiration was greatest at 0 to 7.5 cm in each positio n and decreased significantly below that depth. Correlation analysis i ndicated microbial activity in ridge-till varied spatially in relation to changes in the soil physical environment. Soil respiration was neg atively correlated with bulk density at each WFPS. The K-sat was posit ively correlated with soil respiration at 0 to 7.5 cm for each WFPS. U nder drier soil conditions, as exemplified by 47% WFPS, aggregates <1. 0 mm and gravitational water were positively correlated with soil resp iration at the 0 to 7.5 cm. Soil environments characterized by bulk de nsity <1.4 Mg m(-3) and K-sat >10 cm h(-1) were associated with respir ation rates >4 and 12 mg CO2-C L(-1) soil d(-1), respectively.