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

22/04/23 1

What is slotting• Segmental deep loosening technique to

reduce recompaction• Deep mixing and placement of ameliorants

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Potential uses of soil slotting

ProblemProblem AmeliorantAmeliorantSodic soilSodic soil Gypsum, sludgeGypsum, sludge

Acid SoilAcid Soil Lime, Gypsum, sludgeLime, Gypsum, sludge

Sandy, heavy claySandy, heavy clay Organic residues, sludge, Organic residues, sludge, (micro) nutrients(micro) nutrients

Nutrient deficiencyNutrient deficiency (micro) nutrients(micro) nutrients

Dense layersDense layers No ameliorantNo ameliorant

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Slot formation

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after Jayawardane et al. 1995

Commercial slotterCommercial slotter

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Slot configurationSlot configuration

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Water logging

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SlottedNot slotted

Air filled porosity

8after Jayawardane and Chan, 1994

Ameliorant mixing

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after Jayawardane et al., 1995

Recompaction

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after Blackwell et al. 1989.

(cm)

Root growth in acid soils

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Fully ameliorated slot

Undisturbed

subsoil

Sludge incorporation

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Yield responses to slotting

CropCrop Increase over controlIncrease over controlWheat (sodic soils)Wheat (sodic soils) 30-60%30-60%

Maize (sodic soil)Maize (sodic soil) 40-65%40-65%

Barley (acid soil)Barley (acid soil) 300%300%

Sugar cane (hard pan)Sugar cane (hard pan) 10%10%

Pasture (degraded)Pasture (degraded) 370%370%

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Slotting vs deep ripping

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SlottingSlotting Deep rippingDeep rippingHigh costHigh cost Moderate costModerate cost

Thorough ameliorant mixing Thorough ameliorant mixing to depthto depth

Poor ameliorant mixingPoor ameliorant mixing

Recompaction controlRecompaction control Re-consolidationRe-consolidation

Less restrictive to soil water Less restrictive to soil water content at operationcontent at operation

Soil water content restrictiveSoil water content restrictive

Sub-soil obstacles could Sub-soil obstacles could restrict operationrestrict operation

Sub-soil obstacles less Sub-soil obstacles less restrictiverestrictive

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 discharge15

Stress fissures along slot wallStress fissures along slot wall

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Slot undisturbed