PENETRATION RESISTANCE TO CHARACTERIZE THE DEPTH AND PERSISTENCE OF SOIL LOOSENING IN TILLAGE STUDIES

Abstract

Soil penetration resistance was used to characterize tillage-induced changes in soil strength, as a functon of soil depth and time, under three reduced tillage systems and a deep tillage study in loam to fine sandy loam, Podzolic and Luvisolic soils. The penetration resistance measurements quantified the depth, degree, and persistence of soil loosening, and potential soil rooting depth in regard to tillage system. Mouldboard ploughing provided a greater degree of soil loosening than chisel ploughing. The potential soil rooting depth of 33 – 36 cm under mouldboard ploughing was decreased to 26 cm under both direct drilling and shallow tillage. Use of a slant-legged subsoiler (i.e., “paraplow”) prior to direct drilling prevented the reduction in soil rooting depth. The depth of soil loosening gradually declined by 30 and 60%, over a 5-mo period, under mouldboard ploughing and the "paraplow" direct drilling system, respectively. Residual tillage effects and soil compaction after deep loosening were quantified by the penetration resistance measurements. The use of penetration resistance to rapidly screen soil depth to critical levels of soil strength demonstrated that under sequential direct drilled systems soil loosening should occur on a regular basis to maintain optimum soil structure on fine sandy loam soils. Key words: Soil strength, penetration resistance, reduced tillage, Podzolic soil, Luvisolic soil