This document discusses soil strength and compaction. It notes that soil strength is influenced by soil moisture and management. Cone penetrometers can quantify relative soil strength. Soil workability and friability are measures of soil quality, with small plastic index and large friability index indicating best workability. Soil is weakest for compaction when it is at its best for planting. Disc seeders are highly sensitive to soil strength. Managing to reduce soil strength and increase moisture at maximum friability is optimal. Generally, soil with high friability and low plasticity close to the plastic limit is most cultivation friendly, but this also makes it best for compaction.

1. Soil:Strength & CompactionJack McHughContributions from Dr Jack Desbiolles (Ashworth et al., 2010) and Baker et al., (2007)

2. Soil StrengthSoil Strength is the soil resistance to deformation and is strongly influenced by soil moisture and management.Cone penetrometers can be used to quantify relative soil strength.Soil workability and friability – Measures of soil quality.Soil moisture thresholds – solid, semi solid, plastic, liquid (Atterberg limits)Small plastic index and Large friability index – best workability.Soil at its best for planting - is also the weakest for compaction.Soil monitoring – soil physical changes over time due to management.Disc seeders are highly sensitive to soil strength.Optimal - reduce soil strength and increase soil moisture at maximum friability.

3. CoverWorkability as influenced by soil moistureMaximum compactabilityGenerally soil with a high friability index and a low plasticity index with FC close to the plastic limit are considered most cultivation friendly.Best for cultivation = Best for compactionSeparate beds from tracksImprove workability:Increase organic matterLow compaction management

4. Soil and Furrow compactionTypical profiles of V,U and inverted T furrow profiles in a silty loam at 15, 20, & 27% moisture content. Heaving (h), cracking/loosening (l), smearing (s) and compaction (c). Triple disc Narrow hoe opener T chisel opener Response of contrasting zero till slot shapes to dry soilconditionsPressing seeds into the base of V & U slots assists emergence

5. Soil and Furrow compactionDrilling into wet soilsResponse seedling emergence and earth worm numbers to three contrasting zero till slot shapes and surface residues in a wet soil

6. Using disc drills in wet and sticky soilsDr Jack Desbiolles. Institute for Sustainable Systems and Technologies, University of South Australia. GroundBreaker 2009 - Issue 50

7. V SlotsU Slots

10. Developed in 2004…“VS – Fast”Field – based soil descriptors & measures

11. for farmers / agronomists