Soil water repellents – no dry topic

Managing water repellency of soil was one of the many hot topics at the 2017 Grains Research and Development Corporation’s Grains Research Updates event held in Perth recently.

Hosted by Phil Ward of CSIRO, the ‘Managing water repellency with minimal soil disturbance’ presentation proved interesting and kept the attendees engaged.

According to Phil, soil water repellency is identified as one of the major constraints to agricultural production in southern and Western Australia, impacting up to 10 million hectares of sandy soils.

Water repellency is caused by hydrophobic plant waxes and microbial by-products that break down and mix with or coat soil particles.

He says the tell-tale sign of dry patches of soil, even after substantial rainfall, can cause poor crop establishment and staggered weed germination, leading to poor crop performance, increased weed management costs, leaching of nutrients through preferential flow and an increased risk of soil erosion.

NACC’s Carbon Farming Coordinator Sarah Jeffery attended the update event and said one of the major interest points from the presentation was hearing that dry seeding actually increases soil water repellency.

Another major theme during the presentation was the use of no-till cropping.  No-till cropping preserves the biopores formed by the plant roots which then act as pathways for water infiltration.  When the soil is cultivated these pathways are destroyed.

Interesting points were also raised that plant emergence from sowing on-row was far greater than when sown in the inter-row, and also that stubble retained with no-till cropping compared with stubble burnt, and soil cultivated also resulted in a greater plant emergence.

Attendees left the update with some strong take-home messages including three of Phil’s golden rules:

  • No-till and residue retention provide an effective management strategy for crop production in water repellent soils, and the techniques can be used either on their own, or to complement amelioration strategies based around strategic deep cultivation.
  • Preserved root pathways in no-till systems can by-pass water repellent soil and allow rainfall to infiltrate. The resulting higher moisture content in the furrows can facilitate crop emergence; growers can take advantage of this by planting near the old crop row.
  • Where feasible, water repellent paddocks should be sown last in the seeding program in order to avoid dryseeding which can worsen the symptoms of water repellency.

To see Phil’s presentation slides click here or the project report click here.

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