1. Soil Slotting to ameliorate subsoil limitations to crop production (first presented in 1991) N. S. Jayawardane, ex CSIRO, Division of Land and Water, GPO Box 1666, Canberra, ACT 2601, Australia. G. Kirchhof*, ex NSW Agriculture, PMB 944, Tamworth 2340, Australia. gk@mpx.com.au J. Blackwell, ex CSIRO, Division of Land and Water, PMB 3, Griffith, NSW 2380, Australia. Currently ILWS Charles Sturt University, Wagga 23/05/2015 1

2. What is slotting Segmental deep loosening technique to reduce recompaction Deep mixing and placement of ameliorants 2

3. Potential uses of soil slotting ProblemAmeliorant Sodic soil Gypsum, sludge Acid Soil Lime, Gypsum, sludge Sandy, heavy clay Organic residues, sludge, (micro) nutrients Nutrient deficiency (micro) nutrients Dense layers No ameliorant 3

4. Slot formation 4 after Jayawardane et al. 1995

5. Commercial slotter 5

6. Slot configuration 6

7. Water logging 7 Slotted Not slotted

8. Air filled porosity 8 after Jayawardane and Chan, 1994

9. Ameliorant mixing 9 after Jayawardane et al., 1995

10. Recompaction 10 after Blackwell et al. 1989. (cm)

11. Root growth in acid soils 11 Fully ameliorated slot Undisturbed subsoil

12. Sludge incorporation 12

13. Yield responses to slotting Crop Increase over control Wheat (sodic soils) 30-60% Maize (sodic soil) 40-65% Barley (acid soil) 300% Sugar cane (hard pan) 10% Pasture (degraded) 370% 13

14. Slotting vs deep ripping 14 Slotting Deep ripping High cost Moderate cost Thorough ameliorant mixing to depth Poor ameliorant mixing Recompaction control Re-consolidation Less restrictive to soil water content at operation Soil water content restrictive Sub-soil obstacles could restrict operation Sub-soil obstacles less restrictive

15. Is there a future in soil slotting? Rehabilitation of severely degraded soils Sludge slotting on forestry lands for sludge disposal Potential uses currently restricted to high value crops Adoption of slotting hampered by cost Potential use for installing a lime-slot around acid-sulphate lands, to neutralise discharge 15

16. Stress fissures along slot wall 16 Slot undisturbed