New generation soil wetters perform in forest gravels

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Results from a series of WA DPIRD trials show new soil-wetting-agent chemistry is alleviating water-repellency constraints in WA’s forest gravel soils

Photo of Dr Stephen Davies
WA Department of Primary Industries and Regional Development researcher Dr Stephen Davies says banded wetting agents are starting to show benefits in trials. PHOTO: DPIRD

With more than three million hectares in Western Australia’s grainbelt considered either moderately or severely water-repellent, researchers are on the hunt for solutions to one of WA’s biggest constraints to grain-growing productivity.

Anecdotally, growers are suggesting the area of soil water-repellence is increasing as management styles, such minimum tillage, dry seeding and lower seeding rates, evolve.

While the recent spotlight has been on soil amelioration or aggressive tillage strategies, some growers are now looking at less costly options, such as banded soil-wetting agents applied at seeding time, to solve their water-repellence challenges.

WA Department of Primary Industries and Regional Development (DPIRD) senior research officer Dr Stephen Davies has been managing GRDC-invested trials in various different soil types across WA’s grain-growing regions for many years, looking at a range of strategies to overcome water-repellence.

Some of the research was undertaken at Kojonup and Meckering in 2015, comparing the effectiveness of soil wetters on forest gravel soils and deep yellow sand.

Looking at the research data, Dr Davies says banded wetting agents are an effective option for growers with forest gravel or loamy gravel water-repellent soils, with new generation chemistry allowing the products to be banded with the seed and applied with other liquids, such as nitrogen. But he says the results were not as conclusive on deep sands, particularly those with overriding constraints such as aluminium toxicity and compaction, where soil-wetting agents have yet to prove their reliability.

“Twenty years ago soil-wetting agents were difficult to apply, but with new chemistries now available banded wetting agents applied at seeding time on furrow using liquid in-furrow injection seeding systems are proving to show real benefits in some of our trials,” Dr Davies says.

The aim of the trials investigating these new soil-wetting agents was not just to see end yield results, but to monitor germination and establishment, ensuring early crop competition against weeds. The trials included the application of wetting agents to the furrow surface, and also banding the agents with the seed through existing liquid banding systems along with urea ammonium nitrate (UAN, liquid nitrogen fertiliser) and other liquid applications such as fungicides.

Dr Davies says the outcomes were very clear on the loamy forest gravels for both canola and cereals, with the new generation banded wetting agents having a positive impact on plant numbers and, ultimately, yield results.

“Our research is showing that wetters banded with the seed, applied through existing liquid application systems, or applied on the furrow surface after the press wheels can improve plant numbers and yield results,” he says.

At the Kojonup trial site, wetters were applied to barley and canola.

In Hindmarsh barley, the wetting agents were banded on the furrow surface at two application rates of one and two litres/ha, or banded with the seed through the existing liquid application system at seeding time.

Plant numbers on this site increased by 50 to 73 per cent compared with the control, and grain yields increased by 15 to 29 per cent. However, the findings showed there was no significant benefit from using the higher application rate of 2L/ha when the wetter was applied to the furrow surface in that season.

In the Hyola® 525 RT canola trial in Kojonup, banded wetting agents improved plant numbers by 37 to 88 per cent, with the research showing higher plant numbers where the wetter was banded with the seed compared with when it was applied to the furrow surface.

This was mirrored in the yield results, where canola yields increased by 9 to 17 per cent when compared with the control, with the biggest increases seen in the experiments where the wetters were banded with the seed, rather than on the furrow surface.

Dr Davies says while other soil-amelioration strategies may see greater improvements in yield results over the longer term, the research is now showing soil-wetting agents are a cost-effective way to overcome water-repellent constraints in the short term on responsive soils.

“The evidence from these trials is clear – if you need a cost-effective strategy that doesn’t involve tillage or clay spreading to improve yields on these forest gravel soils, soil wetters are now a real consideration,” he says.

He says results from the trials in Meckering, on deep yellow sand, were inconclusive, but could have been due to the terminal drought conditions in September and October, plus the added frustration of severe frost events. While results in these plots showed soil wetters improved Mace wheat establishment by 30 to 40 per cent, ultimately there was no yield benefit from the use of wetters.

Why this result occurred is not clear, but Dr Davies says more trial work is needed to ascertain the real value of banded wetting agents on this particular soil type, since results from other trials on deep sands have been highly variable. “For every sandy soils trial site that has not responded to the wetting agents, we have achieved positive responses at other sites. This means that more work needs to be done trialling wetters in these soil types in different environmental situations,” Dr Davies says.

“What we can say is that there is more chance of a positive response if using the banded wetters when dry seeding, which increases expression of water-repellence.”

Running parallel to these trials, Australian spray oils and adjuvant technology company SACOA has been trialling the effectiveness of a new wetter chemistry that aims to increase soil moisture holding capacity in the root zone. Many of the trials have been running in the same paddocks as the WA DPIRD trials.

SACOA’s national technical and marketing manager Matt Sherriff says this new in-furrow moisture attractant and retention agent, called SE14TM, has been developed with the aim of increasing plant establishment, improving early crop vigour and increasing crop competitiveness with weeds.

Apart from the trials in Kojonup and Meckering, a series of fully replicated independent national trials were established in 2014 and 2015 in wheat, barley, canola, sorghum, chickpeas and cotton crops across WA, Victoria, NSW and Queensland. Large-scale demonstration sites were also established in WA.

Treatments included incorporating the SE14TM with a range of liquid in-furrow products used at seeding such as liquid UAN (Flexi-N®), trace elements including zinc and copper, and in-furrow fungicides and insecticides.

Mr Sherriff says all these independent trials showed increases in plant counts, with yield improvements from the large-scale grower demonstration sites ranging from 2 to 23 per cent with an average yield of 12 per cent.

In 2015, three out of the five large-scale grower trials showed significant yield improvements, with the largest response on forest gravel at Arthur River.

Dr Davies says crop response to banded soil wetters is highly dependent on soil moisture conditions at the time of sowing. In the WA DPIRD research trials, results showed that when using a banded wetting agent for dry seeding on repellent sands, average grain yield responses were 11 per cent (for 10 trials) but the results were quite different when seeding after reasonable rainfall, where there was no yield advantage (seven trials) from using banded wetters.

“The pattern is similar for the repellent forest gravels except that these soils are more responsive to banded wetters with an average yield increase of 18% (6 trials) when dry sown and a smaller increase of 5% (3 trials) when sown after rain,” Dr Davies says.

According to SACOA’s Mr Sherriff, his trials demonstrated accurate wetter placement was the key to maximising the product’s effectiveness. “We found there was a direct correlation between the liquid stream placement relative to the seed, with the highest plant number increases being recorded where the liquid stream was placed within two centimetres of the seed,” he says.

Mr Sherriff says the trials uncovered a number of additional benefits resulting from the use of SE14TM such as improved nutrient uptake and decreased soil-borne disease and improved legume nodulation.

“Perhaps most importantly, we are also seeing decreased weed numbers – presumably resulting from increased early crop competitiveness where SE14TM has been used,” he says. “This is likely to have resulted from improved soil moisture relations in the root zone.”

Dr Davies says growers should look at their soil types and consider any additional constraints apart from water-repellence before considering the use of a banded wetting agent. “The interaction between soil wetters and other farm inputs, such as herbicides and fungicides, needs further investigation to ensure growers know exactly what the effect of soil wetters will be on their yield outcomes,” Dr Davies says.

More information

Dr Stephen Davies
08 9956 8515