Soil physical qualities in an Oxic Paleustalf under different tillage and stubble management practices and application of S theory

► S theory was validated using soils from a 26 years old tillage/stubble experiment. ► Direct-drilling improved soils’ bulk density, OC, aggregation and friability. ► The S values were well correlated with the other soil physical quality indicators. ► S values ranged 0.030–0.046 associated with poor and good soil physical quality. ► S can be used as an overall index of soil physical quality. The common soil physical quality indicators are related to each other because they all reflect soil structure, but to measure all of these parameters would be very time consuming. Therefore, it is desirable to obtain one simple index for overall assessment. The soil physical parameter, S, may serve this purpose but the theory needs to be validated on soils affected by different management practices. Therefore, in this paper, soils from a long-term tillage/stubble experiment which commenced in 1979 in New South Wales, Australia were analysed for treatment effects on aspects of soil physical quality and on the S value. The treatments ranged from direct-drilling, stubble-retention through to multiple-cultivation stubble-burnt and also included a wheel track vs. non-wheel track comparison. Results showed that after 26 years of different tillage and stubble management practices, significant changes in soil physical qualities were detectable at 0.05 m depth. The direct-drilling soil had lower bulk density, higher soil organic carbon and improved water-stable aggregation (>0.25 mm aggregates) and friability. The S values obtained from the soil water retention curves were well correlated with the other soil physical quality indicators determined in this research and covered the range of S values from 0.030 to 0.046 associated with soil physical qualities in the poor and good categories. It is concluded that S value can be used as an overall index of soil physical quality for soils under different tillage, stubble and field traffic treatments.