Maintain water channels
GroundCover™ Supplement Issue: 118 | 31 Aug 2015 | Author: Dr Margaret Roper, Dr Phil Ward and Dr Stephen Davies
A range of management strategies has been developed to offset the impact of water repellence on crop production. The effects of mitigation practices can last from a few months (furrow and on-row sowing) to two years (wetting agents). Mitigation strategies minimise the effects of water repellence without reducing the non-wetting status of the soil (Table 1). Amelioration strategies correct or remove water-repellent topsoil with benefits usually lasting three years or more (see Long-term non-wetting remedies).
| Management tool
||Operating cost (excluding capital)
||Timing|| Longevity of benefits
|On-row versus inter-row
||All repellent soils
||Predominantly capital cost of suitable seeder
||Sowing|| 1–2 months
|Improved furrow sowing
||All repellent soils||Cost of winged points or boots versus standard knife points
||Sowing|| 1–5 months
|Furrow sowing with banded-applied wetting agents
||All repellent soils||$10–12/ha/year||Sowing|| 2–3 months
|Blanket-applied wetting agents
||Loamy gravels and loamy sands
||$25-50/ha/year depending on rate required
||Pre-sowing||Up to 2 years
|Zero-till and full stubble retention
||All – except rocky and stony soils
||Predominantly capital cost of zero-till seeder
|Liming||All acidic and repellent sandy soils
||~$75/ha for 2t/ha, but varies depending on transport distance
|| Ongoing – provided optimum pH is maintained
Water repellence in deep sands has typically been managed using furrow sowing to direct water towards the germinating seed. However, furrow sowing on non-wetting soils is not always successful when using narrow points as water-repellent soil can flow into the furrow to mix with seed and fertiliser.
Winged seeding systems can throw repellent sand away from the furrow and have been shown to lift wheat establishment rates and grain yields over narrow points (Figure 1).
Department of Agriculture and Food, WA (DAFWA) research showed winged boots in combination with paired seeding lifted crop yields on non-wetting soils by about 20 per cent compared with five per cent for winged boots alone (Figure 2).
These initial field results are promising; however, further evaluation is needed to better understand the movement of repellent soil and its relationship to seed placement under various moisture conditions and water-repellent soil types.
Sowing seed on or close to the previous year’s cropping row rather than on the inter-row can improve plant establishment on non-wetting soils as the old root channels act as pathways for water infiltration. Research at Pingrup on WA’s south coast found soil water contents were significantly higher on the row than the inter-row in non-wetting soils and that water repellence – as measured by the molarity of ethanol droplet (MED) method – dropped over time in the ‘on-row’ compared with the inter-row (Figure 3). Water repellence on the row reduces residues over time because the higher soil water content encourages the growth of wax-degrading bacteria, which work to strip the soil particles of their water-repellent, waxy skin.
Stubble and no-till
Despite concentrating the waxy compounds responsible for water repellence at the soil surface, no-tillage systems are associated with reduced non-wetting symptoms due to the formation and maintenance of bio-pores created by old roots that act as channels for water flow into the soil (Figure 4a).
In a cultivated soil these bio-pores are broken up, which restricts water entry (Figure 4b). Root channels persist in no-till systems even after the crops have matured, conducting water into the soil well after the establishment of the new season’s crop (Figure 4c).
When non-wetting soil is cultivated, water entry into the crop rows depends on the development of new root channels by the emerging crop, but the surface soil between the new rows remains dry (Figure 4d).
Banding a wetting agent in the furrow base behind the press wheels requires 20 to 50 per cent less agent than a blanket application across the entire paddock. Early generation wetting agents were shown to increase crop establishment by 10 to 18 per cent depending on rate (Figure 5), but some trials also delivered yield losses due to the negative impact of the wetter chemistry on water retention and nutrient leaching (Table 2). Newer, shorter-lasting and biodegradable banded wetting agents have since been developed that have less impact on soil water retention and nutrient leaching while providing better wetting-up of the soil and improved crop germination. To be successful, wetting agents need to be applied as a continuous band to the base of the furrow. Furrow infill, soil throw from adjacent seeding tynes or placement onto soil that is still moving can all reduce the efficacy of the banded surfactant.
|Trial||Number of comparisons
||Per cent yield change
||Yield change range (kg/ha)
||16||144||9||–340 to 550
||10||204||16||0 to 490
||6||–50||–2||–340 to 550
|DAFWA 1993 cereals
||4||125||8||–100 to 300
Application rates 1 to 2L/ha. Costs range from $8 to $16/ha. Benefits last one year.
More information:Dr Margaret Roper, CSIRO Agriculture Flagship,
08 9333 6668,
Dr Phil Ward, CSIRO Agriculture Flagship,
08 9333 6616,
Dr Stephen Davies, DAFWA,
0408 439 497,
GRDC Project Code CSP00139
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