Maintain water channels

GroundCover Live and online, stay up to date with daily grains industry news online, click here to read more

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
Soil type
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
 Sowing Ongoing
Liming All acidic and repellent sandy soils
~$75/ha for 2t/ha, but varies depending on transport distance
Usually pre-sowing
 Ongoing – provided optimum pH is maintained

Furrow sowing

Bar chart showing grain yield on a variety of repellent soil types at Badgingarra, WA

Figure 1 Grain yield on a moderately repellent pale deep sand, a severely repellent sandy gravel and a mildly repellent yellow deep sandplain at Badgingarra, WA using knife points or a winged point-paired row seeder system.

SOURCE: DAFWA

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.

Bar chart showing wheat establishment on a moderately repellent deep sand and severely repellent sandy gravel at Badgingarra, WA.

Figure 2 Wheat establishment on a moderately repellent pale deep sand and severely repellent sandy gravel at Badgingarra, WA, using knife points or a winged point-paired row seeder system.

SOURCE: DAFWA

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.

On-row seeding

Soil water content and repellency levels over time on-the-row and the inter-row of non-wetting soils sown to wheat a Pingrup, WA, in 2013

Figure 3 Soil water content (a) and repelllence levels over time 'on the row (b) and the 'inter-row' of non-wetting soils sown to wheat at Pingrup, WA< in 2013.

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

Photo compilation (4) showing variation in soil water movement between cultivated and no-till non-wetting soil

Figure 4 Variation in soil water movement (blue dye) between cultivated (b and d) and no-till (a and c) non-wetting soil.

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).

Wetting agents

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.

Bar chart showing lupin, barley and wheat crop establishment improved with blanket and banded applied wetting agents

Figure 5 Lupin, barley and wheat crop establishment improved with blanket and banded applied wetting agents.

Trial Number of comparisons
Average yield
Per cent yield change
Yield change range (kg/ha)
All trials
16 144 9 –340 to 550
Dry sown
10 204 16 0 to 490
Wet sown
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.

SOURCE: DAFWA

More information:

Dr Margaret Roper, CSIRO Agriculture Flagship,
08 9333 6668,

margaret.roper@csiro.au;

Dr Phil Ward, CSIRO Agriculture Flagship,
08 9333 6616,
phil.ward@csiro.au;

Dr Stephen Davies, DAFWA,
0408 439 497,
stephen.davies@agric.wa.gov.au

Next:

Long-term non-wetting remedies

Previous:

Dry seeding puts time pressure on moisture

GRDC Project Code CSP00139

Region West