Researchers gain ground on soil water challenge

Researchers gain ground on soil water challenge for northern grain growers

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The effective capture and storage of water is a holy grail for northern grain growers.

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DAF extension officer David Lawrence says early results suggest that cover crops can increase net water storage across fallows with limited ground cover and deliver dramatic yield increases in subsequent cotton and wheat crops. Photo DAF

DAF extension officer David Lawrence says early results suggest that cover crops can increase net water storage across fallows with limited ground cover and deliver dramatic yield increases in subsequent cotton and wheat crops. Photo DAF

The effective capture and storage of water is a holy grail for northern grain growers who have long strived to harness the productive benefits of every millimetre of rainfall.

It's underpinned enormous change in farming techniques over the years with the adoption of practices like zero tillage, but researchers believe that significant additional productivity gains are possible with a well-managed cover cropping program.

"However, the measured yield gains for these treatments were 950 kg/ha, 1461 kg/ha and 1129 kg/ha respectively, representing increased returns of between $250 and $380 /ha.

"These are quite remarkable results and while unlikely to occur often, may demonstrate the value of retained surface moisture for good establishment."

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While the industry is becoming increasingly more adept at utilising available soil water and improving individual crop performance in dryland systems, the effective capture and storage of rainfall across the whole farming system remain major challenges for northern grain and cotton growers.

For a number of years GRDC farming systems research investments have been assessing ways to improve this system water use, and to achieve 80 per cent of the water and nitrogen limited yield potential in northern cropping systems.

This work adds to past research by GRDC's Eastern Farming Systems project and Northern Growers Alliance (NGA) trials that suggested cover crops and increased stubble loads can reduce evaporation, increase infiltration and provide net gains in plant available water over traditional fallow periods.

At the Bungunya site for example, the biggest yield increases were from the cereal cover crops, especially the late-terminated millet and the sorghum. Photo DAF

At the Bungunya site for example, the biggest yield increases were from the cereal cover crops, especially the late-terminated millet and the sorghum. Photo DAF

"Consequently, cover crops may be a key part of improved farming systems providing increased productivity, enhanced profitability and better sustainability," Dr Lawrence said.

Cover crops are typically used in southern Queensland and northern NSW to overcome a lack of stubble and protect the soil following low residue crops such as chickpea and cotton or following skip-row sorghum with uneven stubble and exposed soil in the 'skips'.

Growers typically plant white French millet and sorghum and spray them out within ~60 days to allow recharge in what are normally long fallows across the summer to the next winter crop.

Research to date has shown that allowing these cover crops to grow through to maturity led to significant soil water deficits and yield losses in the subsequent winter crops.

"However, the Eastern Farming Systems project showed only small deficits, and even water gains, accrued to the subsequent crops when millets were sprayed out after six weeks, with average grain yield increases of 0.36 tonnes/ha," Dr Lawrence said.

"Furthermore, NGA work supported by GRDC is indicating that the addition of extra stubble (from 5-40 t/ha) after winter crop harvest appears to reduce evaporation, with initial studies showing between 19 mm and 87 mm increases in plant available water.

"These gains will be valuable if validated in further research and captured in commercial practice."

For more information on the cover cropping research project, Dr Lawrence's 2019 Goondiwindi GRDC Grains Research Update paper is available here.

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