MOREE, NSW, farmer Rob Blatchford used a Nuffield scholarship to go looking for a better cover crop than millet, but found more questions than he bargained for.
The emerging science of broadacre cover-cropping has infinite variation, Mr Blatchford found, but one principle in particular struck him: use as many species as you can.
"Some of these people are throwing everything they can find into the mix," he said. "If it grows, they'll plant it."
The more species, the better the soil nutrient cycling and tillage effect of roots in the soil, and hopefully, the less reliant the farmer is on purchased inputs.
As a result, Mr Blatchford returned to his Moree cotton farm with the realisation that he's not just looking for a new species, but a whole suite of them.
A specialist cotton grower, Mr Blatchford has been using French white millet as a cover crop to hold the soil together after the pupae-busting tillage that follows the cotton harvest. Pupae-busting is used to disrupt the life-cycle of the Helicoverpa moth, and is mandatory for cotton growers using Monsanto's Bollguard varieties.
Millet is a handy, cheap cover crop favoured by croppers on the black soil plains, but Mr Blatchford said it only does the one job - providing cover - and doesn't enhance the soil.
He went on his Nuffield looking for a "silver bullet" species to replace or complement millet, probably a leafy, fast-growing legume.
After meeting - among others - French farmer Sarah Singla, a fellow Nuffield scholar, and North Dakota organic farmer Gabe Brown, he realised that this dream-species "probably didn't exist".
In southern France, Ms Singla uses cover crops on shallow, acidic soil to lift fertility. France imposes restrictions on fertiliser use to prevent pollution of waterways and aquifers.
As well as nitrogen-fixing legumes, Ms Singla's cover crops include turnip and buckwheat. The turnip root helps break up her shallow soils; buckwheat's root exudates help liberate locked-up phosphorus in the soil.
Gabe Brown also uses diversity as a tool, aiming for a polyculture mix of tap-rooted and fibrous-rooted species to organically till the soil.
Where possible, he uses native species adapted to cycling nutrients in local soils.
"He believed that cover crops should mirror nature, and where nature was left to grow without intervention, many species grew to cover the land," Mr Blatchford said.
But Moree isn't North Dakota or France.
In North Dakota, Mr Brown's diverse cover crops are killed off by winter snow before his summer planting. At Moree, Mr Blatchford needs to do the killing.
That ruled out one of his early ideas, peanuts, which don't die easily, and limits his options in other directions.
"Natives would be great, but where do you get your seed from?" Mr Blatchford said.
"There's a lot of native vetch growing here, but how do I get enough seed to cover the acres?"
Pressed for time after his Nuffield, he's mixed this year's millet cover crop with vetch. Right now the vetch, a winter crop, isn't handling the hot, dry summer that Moree is experiencing.
But if Mr Blatchford moves up the food chain to commercially available peas or beans, he's up for far greater expense than he has been for cheap millet.
He's wondering whether he moves to a winter cover crop. He's been planting in summer so the soil would store enough moisture between the cotton harvest and cover-crop planting to ensure a good strike.
Winter would widen his species options, but it might also means he has to push out his cash-crop rotations from every two years to every three - "short-term income pain for long-term soil gain".
Mr Blatchford's scholarship, sponsored by Grain Growers Ltd, took him to Brazil, USA, France, Turkey and Ukraine.
It widened his horizons, but also his field of enquiry - and as a result, he's still looking for answers.
Email Rob Blatchford at firstname.lastname@example.org