Topsoil Properties as Affected by Tillage Systems in the Rolling Pampa Region of Argentina

Improved topsoil structural quality is expected under no-till farming, but soil physical constraints can develop under continuous no-till. Our objectives were: to evaluate the properties of loam, silty loam, and silty clay loam soils under various management practices on a regional scale; to clarify the relationship between soil organic matter pools and soil physical properties; and to find a minimum set of topsoil properties to characterize trends established by tillage. Thirty-nine loam, silty loam, and silty clay loam soils were sampled from cropped fields managed using conventional tillage (CT) and no-till (NT) as well as six undisturbed soils (uncropped). The A horizon thickness did not differ among soil textural groups and was 4 cm thicker in uncropped soils. Total and particulate organic C were significantly affected by management (uncropped > CT = NT, P < 0.001). Soil structural instability of uncropped soils (0.317 mm) differed from CT soils (0.723 mm) but not from NT soils (0.573 mm). Soil structural instability was negatively related to total and particulate organic C, and no relation was found with the resistant organic C pool. Water infiltration rate was the only topsoil property affected by a significant texture x management interaction. Lower infiltration rates in NT silty soils were caused by platy structural forms with horizontal pores. Soil penetration resistance (0-5 cm) was 0.77 MPa higher in NT than in CT soils. A minimum set of topsoil properties to evaluate tillage management includes structural instability, total or particulate organic C, infiltration rate, and penetration resistance.