Digging deep to solve HRZ water issues

High rainfall zone growers grapple with fluctuating soil water levels


Water Resources
Hamilton grower Todd Venning is experimenting with winter-spring canola crosses and methods of managing plant available water. PHOTO Brad Collis

Hamilton grower Todd Venning is experimenting with winter-spring canola crosses and methods of managing plant available water. PHOTO Brad Collis

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Too much water early and not enough later is a big challenge being addressed for HRZs.

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One of the frustrations of cropping in many high-rainfall zones (HRZs) is the struggle to manage too much soil water in the first half of the growing season and then, by late spring, not having enough plant available moisture to finish the crop.

In winter, the water ponds above a heavy clay base before slowly being absorbed. So the water is still there, says Hamilton, Victoria, grower Todd Venning, but the clay absorbs it.

What many have been doing since grain growing became a major HRZ enterprise is trying to find a way to make that water accessible for plants when it is most needed, Todd says.

Consequently, there has been an unrelenting effort to change, either agronomically or mechanically, the plant available water (PAW) of the clay layer.

At stake is the potential, in Todds view, to double-crop and grow pasture if this can be achieved.

This would mean a 10-year average for cereal crops of about 8 to 9 tonnes per hectare and canola yields in the order of 5t/ha.

What many have been doing since grain growing became a major HRZ enterprise is trying to find a way to make that water accessible for plants when it is most needed - Hamilton grower Todd Venning

Techniques tried over the years include deep-rooted pasture species, such as lucerne, to try to break into the clay and summer crops, such as sunflower and maize, to also try to open it up. Nothing has yet emerged as a clear answer.

Todd, however, is not giving up. He believes getting organic matter such as manure into the clay would change its structure enough to break the claywater bond and give crop roots access to that water.

Several years ago he borrowed a deep-ripper developed by Agriculture Victorias Dr Renick Peries to place manure deep into the soil.

The results over a 9ha site were promising and Todd is now looking for a more commercially viable unit.

We gained about 50 millimetres of extra PAW from that treatment, but the machines capability was limited," Todd says.

"Weve estimated, based on other trials, that we could get an extra 100mm of PAW if we can treat clay thats 60 to 80 centimetres down, and even more if we can get down to a metre.

At that level, Todd believes theres the potential to access an extra 200 to 250mm of PAW.

That would pretty much alleviate all of our waterlogging problems and deliver a massive jump in crop yield potential," he says.

Todd has also been involved in trialling new winter-spring canola crosses that are showing improved yield potential over conventional spring varieties, in his situation because stem elongation extends further into spring.

The cold soil temperatures and the waterlogging we usually experience in August make conventional varieties lodge and crash, he says.

GRDC Project Code: DAV00141

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