Trials help plains growers improve fallow efficiency

Trials help plains growers improve fallow efficiency


Water Resources
The stripper front used to pluck grain from the heads to retain full stubble height and volume. PHOTO: Liz Wells

The stripper front used to pluck grain from the heads to retain full stubble height and volume. PHOTO: Liz Wells

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GRDC-funded trials look at the effect of increasing ground cover.

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Trials being conducted by the Northern Grower Alliance (NGA) in north-west NSW and southern Queensland are shedding light on the potential for increasing fallow efficiency through the retention of additional ground cover.

Now in their third year, the GRDC-funded trials are looking at the effect of increasing ground cover with the aim of improving crop yield potential through reducing evaporation losses and increasing stored soil moisture, which could also reduce the amount of planting rain required to sow crops.

NGA project manager Brendan Burton says the trials aim to provide growers with a proof of concept that farming methods which go beyond zero-till can improve ground cover to better retain soil moisture in areas where rainfall patterns are anything but safe.

Brothers David (left) and Peter Ricardo inspect wheat stubble left by their new stripper front on the familys Walgett property, Eurie Plains. PHOTO: Liz Wells

Brothers David (left) and Peter Ricardo inspect wheat stubble left by their new stripper front on the familys Walgett property, Eurie Plains. PHOTO: Liz Wells

The impetus for the project came from NGAs Walgett Local Research Group (LRG).

They made maximising soil-water accumulation their top priority, which was not surprising following 2013 and 2014, when inadequate moisture prevented any crops from being planted, Mr Burton says.

A further dry year in 2015 highlighted the problems faced by growers who lose significant amounts of soil moisture through evaporation, which can lock them out of planting windows year after year.

Accumulating more soil water obviously drives higher yield potentials, but if we can also maintain the moisture for longer in the topsoil, it will give growers more ability to plant on time, and into a wider planting window.

Trial sites expand

Initial trials were established in 2015, one at the Walgett property of agronomist Greg Rummery and the other at Brad Colemans property at Bullarah, 60 kilometres west of Moree.

Further trials were established last year, again at Bullarah and also at Andrew Earles property at Mungindi. These sites will host trials again in 2017; a site at Macalister on the Darling Downs in Queensland has also contributed to results.

The trials examined the effect on soil water of applying baled straw to create added ground cover at rates of between five and 40 tonnes per hectare compared with conventionally harvested standing stubble and bare fallow.

The key question we are asking is: if ground cover levels are increased to over 100 per cent to reduce evaporation, can soil-water accumulation be improved? Mr Burton says.

Small-plot work has indicated the addition of extra ground cover can increase the depth of soil water accumulated by up to 50 to 60 centimetres compared with standing stubble, with reduced evaporation losses considered the most likely cause.

Outside the norm

Mr Burton says one of the main drivers for the fallow efficiency trials has been that current soil water models only go up to 100 per cent ground cover (when the soil cant be seen when looking straight down; more than 100 per cent ground cover indicates greater mulch depths). What we are evaluating is going beyond this and accumulating a layer of mulch across the soil surface.

The small-plot trial sites have already demonstrated that increasing the level of ground cover beyond 100 per cent was providing improved fallow water efficiency. In these trials, 100 per cent ground cover was occurring at about 10t/ha of straw spread evenly over the soil surface.

Stubble management evaluated

Mr Rummery says the trials are providing an insight into ways in which growers can maximise the benefit of heavy stubble loads in the following and subsequent crops.

If youve got a lot of cover, you can decrease evaporation. The question is: how can we put that into the paddock?

If youve got a lot of cover, you can decrease evaporation. The question is: how can we put that into the paddock? - Greg Rummery

Retaining as much stubble as possible appears to be a much more economically viable solution than buying-in straw in far-flung farming areas such as Mungindi and Walgett, but Mr Rummery says this might present problems in itself. We are looking beyond zero-till for more moisture, and at retaining more crop residue, he says.

We know that mud drives everything, and these soils have the ability to hold moisture, but we also know that planting through 20t/ha of straw is not going to be possible using current seeding equipment and set-up.

The challenge is to find a way to achieve the benefits commercially and economically.

Another trial recently established by NGA with brothers David and Peter Ricardo at Eurie Plains, east of Walgett, could provide some answers.

In 2016, the Ricardos bought a stripper front, which plucks grain from the heads to retain full stubble height and volume.

Following well-timed planting and in-crop rains throughout the Walgett district, the Ricardos harvested a wheat crop that averaged 6t/ha and left behind a stubble load equivalent to 14t/ha of dry matter.

Peter and Davids stripper front has left a large body of standing stubble which will allow us to measure the effect on soil water compared to slashed stubble which has been laid over the fallow, Mr Burton says.

NGA is installing capacitance probes at trial sites on Eurie Plains to monitor soil water and provide a constant data flow.

In addition to three commercial-scale one-kilometre strips at Eurie Plains, which have full-height, conventional-height and ground-level stubble, small plots will compare results where stubble has been removed.

These plots will evaluate the effect of slashed full-height stubble which has been laid flat and held in place with mesh to simulate rolled stubble.

We need to look at ways to retain as much cover as we can without jeopardising the effectiveness of the next crop we plant, Mr Rummery says.

Considering the benefit of more soil water than conventional stubble has left them with, it is a problem the Ricardos are happy to have.

They hope to be able to plant cotton in spring using their Boss planter with twin disc openers.

That will depend on what the stubble looks like come October or November, Peter Ricardo says.

The Ricardos are considering other stubble management strategies, which include swathing and leaving stubble in windrows over the planting row before shifting it to between rows immediately prior to seeding.

This approach may allow more control over planting date and negate the need for a planting rain.

More Information: Brendan Burton, 0428 979 170, brendan.burton@nga.org.au

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