Soil water repellence - setting up seeders for banding wetting agents

Page last updated: Wednesday, 28 February 2018 - 11:51am

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Banded wetting agents can make dry furrow sowing of water repellent soils more reliable. Soil wetting agents help water enter more quickly and evenly along the length of the furrow, providing more consistent wetting up of the seed zone. There are technical challenges and certain requirements involved in the setup of seeders for banding soil wetting agents. The sprayed stream of wetting agent needs to be applied either to stationary soil in the base of a stable furrow behind the press wheels or banded in the furrow within 20mm of the seed.

Banding wetting agent during the seeding process involves spraying a continual stream of liquid products which may contain combinations of wetting agents, surfactants and water retaining substances in a narrow band onto the base of a furrow or banded in the furrow near the seed when dry sowing a crop or pasture in water repellent soil.

Banded wetting agent makes dry furrow sowing more reliable. Many products are also biodegradable and short lived or include water adsorbing compounds to reduce leaching effects from the wetting agent (reducing surface tension allows soil to wet up more easily and drain more easily). Addition of nutrients and pesticides to wetting agents for more efficient targeted applications has also been successfully tested.

A key role of this method seems to be improvement of crop establishment when dry sowing into dry water repellent topsoil over moist subsoil at about 100mm, due to earlier rains and subsequent drying. If the point works too deeply it can mix moist soil with dry and encourage ‘malting’ of the seed. A shallow point or disc can place the seed in dry soil, but there are risks of fine repellent material being graded back into the seed zone with a knife point. Thus the band of wetting agent enables more reliable establishment with such shallow seeding methods. The method is also potentially very adaptable to variable rate application where soil type and distribution in paddocks is not uniform and wetting agents can be applied only to those soil types that are repellent.

Response to different products can vary from soil to soil and region to region, therefore local, on-farm testing and good commercial advice on the methods and products is advised.

Effective application of banded wetting agents

Traditionally banded soil wetters were applied to the surface of the furrow behind the press wheels but recently soil wetter products have been developed that can be banded in the furrow near the near the seed and are compatible with other banded liquid products.

Surface banding of wetters

Surface banded soil wetters work when water harvested from the furrow ridges meets the wetting agent product at the base of the furrow. The product dissolves into the water and increases the wetting power of the harvested rain by lowering the surface tension of the water, allowing it to penetrate pores between the repellent soil particles more easily. This helps ensure that the whole length of a furrow is wetted up, rather than higher sections of the furrow base shedding water along the furrow to adjacent shallow lower areas; resulting in sections of row remaining dry beneath the furrow with ungerminated seed.

When applying the banded soil wetter it should be sprayed as a continuous stream onto stationary soil at the base of furrow, so it is not buried, remains at the surface and can directly meet the rain when it is harvested from the furrow wall. Soil which can bury and interfere with the surfactant mainly comes from:

  • dry soil flowing around the sides of the press wheel
  • soil pushed sideways into a furrow made by a preceding tine nearer the front of the seeder
  • soil falling into the furrow from following windy weather
  • the stream spraying into a tumbling mass of soil ripped from the edge of the furrow by relatively narrow rectangular press wheels which rips up the edge of the furrow (Figure 2). This breaks up and mixes up the stream of product so it is no longer a continuous unbroken band in the base of the furrow.
V-shaped press wheel forming a furrow in water repellent soil
Figure 1 Firming of a furrow in water repellent sandy topsoil using a V-shaped profile press wheel which does not disturb the side walls of the furrow leaving stable furrow base onto which banded wetting agent is being applied

Furrow formation using press wheels with a V-shaped (Figure 1) or U-shaped profile causes little disturbance of soil on the furrow edges compared with a rectangular shaped press wheel profile (Figure 2), where the angular sides of the press wheel rip up and disturb the soil in the furrow edges.

Firming of a furrow in water repellent sandy topsoil using a rectangular shaped profile press wheel
Figure 2 Firming of a furrow in water repellent sandy topsoil using a rectangular shaped profile press wheel which tends to flick up the side walls of the furrow resulting in a tumbling mass of soil onto which banded wetting agent is being applied

Banding in the furrow near the seed

Banding soil wetters in furrow results in a band of the product being placed either along side or above the planted seed row. As water infiltrates unevenly into the repellent soil the band of wetter acts like a 'wick' with water being drawn along the seed row, creating a 'sausage' of wet soil around the seed. Some soil wetter products are compatible with other liquid products such as UAN, micronutrients and fungicides and so can be applied in a tank mix. In order to effectively wet the seed row the wetter needs to be placed within 30mm of the seed. Care needs to be taken if using the product in conjunction with UAN which can damage germinating seed, particularly canola, in which case the product should just be applied in water. Only soil wetter products recommended for in-furrow banding should be used and jar tests can be conducted to check compatability with other liquid products.

Image shows soil wetter being banded behind a typical knife point for sowing broadacre crops using a liquid banding system. It demonstrates how liquids, including  soil wetters, can be banded near the seed.
Figure 3 Soil wetters can be banded near the seed using a liquid kit on seeder in repellent soil allowing improved wetting of the crop row and better crop germination

Setting up band spray application equipment

A number of application set-up options are available to growers once ground speed, application rates and row distance has been determined. Band spraying wetting agents utilises widely available sprayer components commonly used in other liquid applications such as liquid fertilisers. These components are relatively affordable costing approximately $30 per tyne assembly, including the capillary tubing down to the press wheel. Modifications to press-wheel assemblies are often minimal and only required to support the delivery tube and solid stream nozzle to deliver the product into the middle of the furrow.

The distribution and metering of product is assisted by TeeJet non-drip valves assembled in groups on a one inch poly manifold mounted in banks close to the back of the seeding equipment. These valves use a stainless steel orifice plate of a size determined by application rate and ground speed. The threaded cap uses a hose tail connector to join the 4-6mm capillary delivery tubing attached to brackets mounted behind the press wheels.

The termination nozzle is a modified micro-drip irrigation nozzle (0.7mm ID) without the spreader, it forms a long solid stream when the manifold is pressurised to about two bar. The pump is usually electric, turning on or off from the cab or from a switch on the lift mechanism. Ground drive pumps have also been used successfully.

Product rates are typically 1-5L/ha and currently cost approximately $6-10 per litre. Water rates are typically kept to 30-50L/ha to minimise tanks size and to allow convenient refilling when the seed and fertiliser is being refilled. The size and mounting of tanks will be dependent of size of tillage equipment as well suitable location to mount on the bar. Otherwise trailer tanks coupled to the rear of equipment are common.


Soil water repellence research is supported by DPIRD and the Grains Research and Development Corporation (GRDC) through DAW00244 Delivering enhanced agronomic strategies for improved crop performance on water repellent soils in Western Australia.