Seeding soil wetters boost crop yields

Seeding soil wetters boost crop yields

Cropping News
University of South Australia Agricultural Machinery Research and Design Centre research fellow Jack Desbiolles. Photo by GRDC.

University of South Australia Agricultural Machinery Research and Design Centre research fellow Jack Desbiolles. Photo by GRDC.

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Water repellence impact could be improved at seeding

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IT is possible to improve grain yield of wheat and barley crops planted in severely water repellent sands by applying low-cost and low risk wetting agents at seeding time.

In a trial run in 2018 and 2019 by CSIRO, several soil-wetter products and application strategies provided consistent and large crop establishment benefits, while also producing up to 0.22 tonnes per hectare (2018/wheat) and 1.07t/ha (2019/barley) extra grain yield.

The research project was supported by investment from the Grains Research and Development Corporation and investigated management options available at seeding time to mitigate the impacts of water repellence.

The two-year trial was conducted in a 270 millimetre growing season rainfall zone at Murlong on the Eyre Peninsula, South Australia, with a soil wetter evaluation trial aiming to compare a number of seeding strategies.

University of South Australia Agricultural Machinery Research and Design Centre research fellow Jack Desbiolles said an estimated 12.5 million hectares of sandy soils in southern and Western Australia were deemed at moderate and high risks of water repellence.

"These 'non-wetting' sands have low fertility and suffer from delayed and uneven wetting, which leads to erratic crop establishment, staggered weed germination and generally poor crop productivity due to low plant densities, low nutrient access, poor weed control and crop damage in areas prone to wind erosion," Dr Desbiolles said.

"Soil wetter chemistries are varied and complex and little is known of their individual suitability to local water repellence which appears to vary in nature, depending on the soil.

"Modern soil wetters typically have both surfactant and humectant properties - surfactants lower the surface tension between water and the soil particles, which allows rainfall to more readily infiltrate into the water-repellent soil, while humectants are designed to counter excessive leaching in a low 'surface area' sands and aid moisture retention."

The benefits of applying soil wetters at seeding time have been evaluated in Western Australia over the past 10 years, showing that banded wetters are most beneficial for dry sown cereals on repellent forest gravels of the South West with less reliable benefits for break crops.

However, benefits of banded wetters are minimal, or at best sporadic, for dry sown crops on deep sands and there is no benefit with sowing into moist soil for any crop or soil type.

Research on the Eyre Peninsula conducted from 2015 to 2017 found that the two soil wetting agents evaluated could significantly improve wheat, barley and lupin establishment and also benefit grain yield, in two years out of three.

Based on the earlier results from WA and South Australia, the soil wetter trial instigated at Murlong aimed to broaden the range of soil wetter types and combinations evaluated under contrasting furrow placement scenarios.

The impacts of 13 different wetting agents, both surfactants and humectants, in single and dual placement configurations were tested over the 2018 and 2019 seasons, with the treatment costs ranging between $12 and $41 a hectare.

The range of commercial soil wetters evaluated included pure surfactants, surfactant/ humectant (S/H) blends and S/H blends enriched with organics/nutrients.

In 2018, the soil wetter treatments increased wheat crop establishment by 25 plants per metre squared on average, with a range of 0 to 58 plants per square meter.

In 2019, the same treatments increased barley crop establishment by 17 plants/m2 on average, with a similar range of 0-56 plants/m2.

"The impact of soil wetter treatments on crop establishment was similar in both years, as confirmed by a strongly positive correlation between results in each year," Dr Desbiolles said.

"No correlation was found between product performance and $/ha cost, indicating that cost is not a useful indicator of performance.

"Interestingly, all furrow surface applied wetters performed poorly at Murlong, while the two seed zone applied, humectant, products performed better."

In 2018, a decile two year for growing season rainfall, the untreated control had an average wheat grain yield of 1.02t/ha.

In the first year, grain yield responses to soil wetter treatments ranged from 0 to 21 per cent, with a maximum response of 0.22t/ha.

Dr Desbiolles said the earlier break of the season and slightly drier season in 2019 saw larger barley crop responses to soil wetters, with the grain yield of the inter-row sown control averaging 1.10t/ha.

"Yield responses to the wetter treatments ranged from +23pc to +97pc, with a maximum increase of 1.07t/ha," he said.

"In comparison, the on-row control introduced in 2019 yielded the highest, providing a 1.26t/ha grain yield benefit.

"The greater yield responses to soil wetters in 2019 may have been influenced by the stability of the water harvesting furrows produced by the seeding system, compared to 2018 when the challenging post-seeding period resulted in early backfilling of the furrows."

Overall, the grain yield responses across all treatments were similar for both years, with a strong positive correlation between the two data sets, suggesting the better treatments may be recommended to growers in this environment.

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