Evaluation of laboratory-measured soil properties as indicators of soil physical quality

Routine soil analyses provide an approach for assessment and monitoring of soil quality and targeted implementation of management practices, but suitable indicators are mostly undefined. We used three long-term experiments on several soil types where maize (Zea mays L.) was grown under different tillage (no till and plow till), rotation (continuous maize and maize after grass), and harvesting (silage and grain) methods to identify suitable indicators for evaluating soil physical quality. Disturbed and undisturbed soil samples were collected, and laboratory-based analyses were performed for water-stable aggregation, saturated hydraulic conductivity, several pore size parameters, penetration resistance at Psi = -10 MPa, and bulk density. Sensitivity to management, expense of measurement, measurement consistency, and relevance to critical physical soil processes were used as criteria to evaluate indicator suitability. Indicators varied significantly seasonally and by soil type, and several showed significant differences and trends between management treatments. Small water-stable aggregates (0.25-2 mm) showed the most consistent and significant treatment differences. Bulk density, available water capacity, and air-filled pores at field capacity (PO > 30) were also related to treatment effects and had low variability. Penetration resistance and effective porosity (PO > 0.2) were not sensitive to management practices, whereas aeration pores and saturated hydraulic conductivity were too variable to use as indicators. Several indicators measured on undisturbed cores may be predicted from those measured from disturbed samples using pedotransfer functions. Small water-stable aggregates (0.25-2 mm), available water capacity, bulk density, and PO > 30 appear most promising as indicators for routine evaluation and monitoring of soil physical quality.