Chasing water efficient crop rotations

Getting the sequence right could increase profit by up to $400 per hectare

Cropping
NSW Department of Primary Industries crop nutritionist, Graeme Sandral, shows the difference between wheat grown on last year's early-sown canola crop (left) and lentil crop (right).

NSW Department of Primary Industries crop nutritionist, Graeme Sandral, shows the difference between wheat grown on last year's early-sown canola crop (left) and lentil crop (right).

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DPI and CSIRO trial into water efficiency over a whole rotation.

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Water is one of farmers most precious resources and a CSIRO and NSW Department of Primary Industries study is looking at how to make the most of it, not just in one year, but over a whole crop sequence.

The project, co-funded by the Grains Research and Development Corporation, has been run across four sites in southern NSW, including Condobolin, Urana, Wagga Wagga and Greenethorpe.

NSW DPI crop nutritionist Graeme Sandral and his team manage the Condobolin, Urana and Wagga sites, while project lead and CSIRO scientist, Dr John Kirkegaard, looks after the Greenethorpe site.

Mr Sandral said the project, now in its second year, measures the dollars earned per millimetres of rainfall, across multiple sequences to find the most profitable combinations and the decision points that generate highest profit for least risk.

"There are various combinations of crop species, wheat, barley, canola, chickpeas, lentils, lupins, vetch and biserrula all being tested in different combinations, to see how sequence decisions provide the best return on investment over the long term and what risk profile is associated with different choices," Mr Sandral said.

Dr John Kirkegaard said a lot of work had been done on the water use efficiency of individual crops, but not on entire crop sequences.

"We often don't follow up," Dr Kirkegaard said.

"You may have a really good early-sown, dual-purpose crop that's highly profitable in a specific year, but if it leaves the soil really dry and the profile doesn't refill, then the following year has the legacy of dry soil and lower yield potential, which could be managed with improved crop choices."

Mr Sandral said although the trial was only in its second year, they had already begun to see this occur at most of the sites.

"Last year's early-sown canola with high nitrogen, produced roots to at least three metres and used a significant amount of water," Mr Sandral said.

"Now you can see that the early-sown wheat growing on those areas this year is starting to hay off badly.

"Therefore, the income over two years gives you quite a different picture to the income over a single year and we are looking to project this out even further across a range of different seasonal conditions".

Economic benefits of a water efficient sequence

Mr Sandral said the trial was based on studies which showed farmers were not reaching their yield potential when it came to maximising water efficiency across several years.

"We want farmers to focus more attention on conserving soil water," Mr Sandral said.

Dr Kirkegaard said they estimated that better sequencing of crops could be worth an extra $150 to $400 a hectare per year, even when each crop was grown with good agronomy.

"That's the kind of economic opportunity that we're chasing," Dr Kirkegaard said.

He said they did a full year of consultation with farmers in 2017 to design the sequences and and the final designs brought three recent innovations together at each of the sites.

An aerial view of the Wagga Wagga trial site.

An aerial view of the Wagga Wagga trial site.

The first was the use of early-sown wheat and canola with and without grazing.

"Dual purpose crops that can be sown in March can be really profitable, they utilise water really effectively and get their roots down deep," Dr Kirkegaard said.

"But the question is then what we do the following year, when we've dried the soil out."

He said the answer to that question relates to the second area of study, what new crop sequences could be used that could accommodate the early-sown crops that leave drier profiles.

"High value legumes like chickpeas, lentils and barley are starting to get a lot of attention in Southern NSW, especially in these dry seasons," Dr Kirkegaard said.

"They tend to have shallower roots and finish their life cycle quickly so they could be a good option to look at following the high-profit canola or wheat grazing crop."

He said the third area was managing nitrogen in the system, either with legumes or with better fertiliser decisions.

"Generally, in Australia we've been running our organic nitrogen and soil fertility down in intensively cropped soils, and that fertility has historically supported our crops," Dr Kirkegaard said.

"If we're not getting that from pastures, or from grain legumes then we're needing more from fertiliser which has become a significant input cost.

"We're particularly interested in comparing nitrogen provided by legume crops and nitrogen provided by fertiliser."

Results from the first year of the trial

Dr Kirkegaard said they had never put these three elements into the one systems experiment and run it over a number of years.

"We're hoping we can provide farmers with information on the consequences in terms of nitrogen and water supply of various crop management decisions, especially on carry-over effects from one crop to the next," Dr Kirkegaard said.

Mr Sandral said last year it was lentils that were one of the highest returning crops, along with Safflower at the Urana site.

"The lentils also left moisture and nitrogen in the soil profile for the wheat that's grown on them this year," Mr Sandral said.

At Wagga and Greenethorpe the highest return was for early sown wheat, canola or vetch that were grazed in winter and then harvested for hay or grain. At the Condobolin site, chickpeas gave the best profit.

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