Grains Research and Development

Improving the effectiveness of furrow sowing in water repellent soils

Stephen Davies and Paul Blackwell, Research Officers,
WA Department of Agriculture and Food, Geraldton

Take home messages

  1. Some knife point seeding systems allow water repellent sandy soil to flow into the open furrow with the seed and fertiliser reducing establishment which is likely exacerbated by dry seeding and smaller less-frequent rainfall events at the season break.
  2. Modifying the seeding system by adding wings to the knife points or using systems that incorporate winged tynes or boots may reduce the flow of water repellent soil into the furrow and reduce the severity of the problem.
  3. Banded in-furrow wetting agents can help water penetrate the water repellent soil in the furrow and improve the efficacy of furrow sowing.
  4. Seeding on the previous year’s crop row can result in improved establishment with the remnant root systems of the previous crop providing pathways that improves water access into the soil.

Introduction

Historically furrow sowing was introduced to water repellent sandplain soils to harvest water into the furrow where the seed was sown which improved crop establishment. Recent evidence, however, indicates that furrow sowing using knife points is often unsuccessful (e.g. Table 1; Fig. 3) and water repellent soil is often concentrated with the seed and fertiliser in the base of the furrow such that the furrow is often drier than the ridge (Table 1). It is suggested that this may be a result of the flow of dry water repellent soil around the knife point and into the slot opened by the knife point ahead of the closer plate and press wheel. This is likely to be exacerbated when the crop is dry sown and establishment may be improved after rain although there will still often be sufficient dry non-wetting loose soil to flow into the furrow.

Table 1. Gravimetric soil moisture content in the furrow compared with the ridge for a
water repellent sand after seeding.

Soil depth (cm)

Soil moisture (g/g)

Furrow Ridge
0-5 0.10 0.19
5-10 0.04 0.16
10-15 0.03 0.10

Improving Furrow Sowing

To improve furrow sowing it is necessary to either prevent dry water repellent soil from falling in behind the knife point or to help water enter the repellent soil in the furrow. Preventing water repellent soil from being concentrated in the furrow may be achieved by adding small wings to the seeding point or boot. These wings appear to cause the soil to lift and move away from the sowing point as it moves through the soil reducing the amount that falls into the furrow. In yellow water repellent sand at Balla winged knife points reduced the water droplet penetration time of soil in the furrow to 9 seconds compared to 15 seconds for soil from the furrow sown with knife points alone (data not shown).

Table 2. Wheat establishment for a seeder fitted with knife points compared to a seeder with winged seeding points and paired rows in two strongly repellent soils at Badgingarra, 2011.

Soil type Wheat Establishment (plants/m2)
Knife points Winged points & paired rows % Increase in establishment for wing points vs. knife points
Sandy Gravel 110 230 109%
Deep pale sand 97 201 107%
A comparison of moisture content of soil sown with knife or winged points at three locations on the previous years' crop rows. Ridge sowing with knife points is most effective at 5% volumetric moisture content compared to 2.5% when sown with winged points, furrow sowing with winged points achieved 4.2% compared to 2.2% knife points, and knife points are more effective than winged points on the ridge wall, at 3.5% compared to 2.8%. 

Figure 1. Volumetric moisture content at 0-5cm in a water
repellent sandy gravel soil sown with either knife points
or points incorporating wings, Badgingarra 2011.

Further research is required to test this but some seeder comparisons on repellent soils of knife points verses other designs which incorporate wings are promising with improved crop establishment where small wings are fitted (Table 2 and Images). Better crop establishment (Table 2) corresponded with improved wetting up of the furrow where winged points were used (Fig. 1). As well as adding wings, reducing the distance between the knife point and closer plate, increasing the speed of seeding with wider row spacing or changing the rake angle of the knife point so it isn’t so steep creating more soil lift may also help, but each of these changes can have other impacts and require further research.

  Sparse wheat growth and uneven distribution across a paddock seeded with knife points. 110 plants per square metre.  Even wheat growth and distribution across a paddock seeded with winged boot and paired rows. 230 plants per square metre.

Further improvement of water entry into repellent soil in the furrow may also be achieved by using a banded soil surfactant in the furrow. The wetting agent is sprayed or injected in a band into the base of the furrow behind the press wheels onto soil that has stopped moving. It is important to try and minimise furrow infill by using press wheels that create furrows with relatively shallow angled sides (eg. V-shaped press wheels). Figure 2 shows how establishment of dry sown lupins using knife points on non-wetting sand at Balla have been more successful with the use of a banded wetting agent.

On row establishment with or without a banded wetter achieves 36 plants per square metre, while between row establishment is less successful at 20 plants with a banded wetter or 6 plants without. 

Figure 2. Lupin establishment in a water repellent deep yellow sand at Balla, 2011, with or without banded wetter and either between or on the previous season's crop row.

Note establishment was improved even more when the lupin rows were sown on the previous years wheat rows, the old roots of which clearly aided water entry into the repellent soil.

While there are other options for ameliorating water repellent soil in the longer term such as claying or one-off use of mouldboard ploughing or spading, these are expensive, may not be suitable for some soil types, and can only be used to treat small areas in a given year. Improving the efficacy of furrow sowing can benefit the whole cropping program in a given season and be relatively cheap to implement.

Acknowledgement

This water repellence research is funded by GRDC and DAFWA through the ‘Delivering agronomic strategies for water repellent soils in WA’ (DAW00204) project. Thanks to the Liebe, Northern Agri, West Midlands and Mingenew-Irwin grower groups and particular thanks to all the growers who have allowed us to work with them on their farms.

Stephen Davies contact:


Ph: 08 9956 8515

Mob: 0408 439 497

Email: stephen.davies@agric.wa.gov.au