BY: ANDREW SWALLOW
Like it or loathe it, the term regenerative agriculture has gained quite a following in the past couple of years. Two advocates of its principles, Jono Frew and Peter Barrett, completed a 27-venue tour of New Zealand travelling from Hokianga to Invercargill in a couple of campervans this winter, relaying their experiences and views to audiences of up to 250 people.
They say they did the tour to “help farmers learn that there is a mindset that empowers them to save money and be more profitable. It involves becoming more aware of the implications of our actions on soil microbiology.”
Building soil health is at the heart of what they believe and more active life in soil makes farms more resilient.
Frew kicked off each seminar relaying how he’d come to be a regenerative agriculture coach following a conventional farming then agchem specialist career, before outlining what he now sees as serious shortcomings in many common farming practices.
Soil tests using aggregated samples from the top 7.5 or 15cm were first in his sights. Those sample depths might be appropriate for ryegrass and white clover, but the diverse pasture and crop mixes used in regenerative systems draw nutrients across a much wider profile. Also, tests such as Olsen P only provide a snapshot of phosphate already in plant available, soluble form, not the reserves which healthy plant roots and associated mycorrhizal fungi might access, he said.
That accounts for why he and farmers such as Peter Barrett see pastures and crops perform well without fertiliser even on soils with nutrient test results well below the “optimum” levels indicated on standard reports.
Monitoring plant health through herbage analysis, and not just for the macronutrients N, P, K and S, is his preferred approach.
“We need to start to think beyond just macro nutrients.”
Soil cation exchange capacity (CEC) was useful because it showed how much nutrient a soil could hold, and to determine the ideal ratio of calcium to magnesium. For example, a soil with a CEC of 15 ideally the ratio should about 7 to 1 he said.
“Too much magnesium and you end up with concrete slabs. Too much calcium and the soil’s too fluffy.”
Carbon or organic matter content of the soil was also a key metric because every 1% increase in carbon allowed a soil to hold another 145,000 to 160,000 litres of water*, and it improved structure.
Good structure was vital to “hold and house” soil biology which itself needed a healthy balance of bacteria and fungi, ideally in the order of one to one, he said.
If bacteria dominated, soil would be too fine and compacted. Bacterial dominance was often a symptom of nitrogen fertiliser use and soil would smell bad as a result.
“If you apply nitrogen to the soil, the bacteria go nuts.”
However, some bacteria, including those in root nodules of leguminous plants, fix nitrogen from air and convert it to plant-available ammonia so they’re not all bad, hence the need for balance.
Fungi give soil more structure, and feed off more complex carbon compounds than bacteria. In the case of mycorrhizal fungi, they act as “the internet of the soil”, allowing the roots of plants coated in them to reach nutrients from vast areas – reaching nutrients kilometres away he said.
However, not all plants benefitted from mycorrhizal fungal associations, including brassicas which was why monocultures of them were so dependent on fertiliser for high yield and got hammered by insects.
Cultivations, herbicides, fungicides and some fertilisers all damaged mycorrhizal networks – “super and DAP burn these guys on contact; they absolutely nuke them,” he noted – but whatever was done to destroy them, given the right soil conditions they’d always come back.
Healthy mycorrhizal fungal populations were why growers such as Barrett were producing mixed forage stands yielding more than 10 tonnes drymatter (DM)/ha with no fertiliser despite soil tests indicating some macronutrients were deficient, he added.
Growing diverse mixes of plants helped build soil biology and structure because each plant species released a unique combination of root exudates so would favour different strains of fungi and bacteria. Similarly, the range of root structures across species, from deep, sub-soil fracturing tap roots to more fibrous shallow roots, could enhance soil structure and resilience of crops to drought.
Frew said diverse stands of forage also boosted stock performance.
“Cows ate less drymatter and yet their production increased: we don’t usually see that in March,” he said, showing a video clip of dairy cows grazing a 35-species mix near the Rangitata.
The mix had been direct-drilled into a compacted, poorly producing grass paddock yet within six months it had increased soil organic matter by half a percentage point, as well as producing a spectacular above ground stand, he said.
Species diversity also built resilience into the system, such that when conditions didn’t favour one species, there would be others that would benefit, and the feed grown didn’t have a tight use-by window.
“These crops stand there waiting for when you need them!”
Short, high stock density grazing was the key to using such feeds and some loss to trampling was good because it helped spread cows’ weight, reducing soil compaction and raindrop or sunlight damage to soil surface structure and biology. Longer residuals also meant less interruption of growth.
“In a perennial stand, you want them to just eat the top: eat a third, trample a third, and leave a third to still capture sunlight. When we leave a bit behind, we can just keep on growing,” Frew said.
That continued growth was particularly important underground: remove too much above ground by grazing or cutting and roots not only stopped growing, but they stopped feeding the soil biota that was essential to gathering nutrients and supplying them to the plant, so the whole system suffered.
Surface litter from trampling helped prevent run-off and aided infiltration of rain or irrigation, he added. Infiltration rate could be checked by banging a wide-bore pipe – drain-pipe or wider – into the soil then filling the top to a set depth, typically an inch, and timing how long it took to soak in. He said he’d seen an inch of water disappear in seconds on undamaged soils but still be there hours later on others in need of remediation.
Traditionally, remediation meant coming in with cultivators to remove compaction but direct-drilled deep tap-rooted plants and certain species of worms could do the same thing, enhancing soil structure and biology rather than bashing it to bits.
Barrett, who has been direct-drilling mixes of dozens of species of forage plants to renovate grazing land at Linnburn Station, Central Otago, told the meeting that approach was succeeding where conventional had failed, and he could do three or four times the area for the same cost.
“We can do 850 to 1000ha with what we used to spend on 250ha.”
Sometimes it would take two seasons of mixed annual cover crops to get the soil biology going and crops pumping but it would get there and when it did, a diverse mix of annuals plus perennials was sown so the latter gradually took over to provide a long-term productive pasture of diverse grasses, lucerne, clovers and herbs.
His mixes typically include 20 to 60 species, with at least one from each of five key plant types: grasses, legumes, brassicas, cereals, and chenopods. It had been a process of trial and error working out what worked best.
“We’ve done 5000ha of this now and we have probably made more mistakes than anyone else in NZ whilst also having the most success!”
However, in Maniototo’s often dry summers, such mixes meant he could now build a reserve of standing feed that would stay green long after surrounding grassland had gone grey, and could be used at any point from December through to the following winter.
Since he started with such mixes in 2014, capital stock numbers have remained constant and trading stock has been introduced into the system to use the extra feed to be utilised.
Barrett’s background
Raised in Wellington, Peter Barrett’s the son of a dentist and took on the family owned property in 2012 having run campervan businesses here and in the United States. The station had been run by managers since 1986 when his grandfather died and, as he puts it, with sheep farming not printing cash during that time maintenance of assets had not been proactive and the “asset needed a lot of love.” Pastures needed to be renewed, fences repaired or replaced, houses tidied up.
Initially he followed standard spray-cultivate-drill advice to establish crops and renew pastures but when a ryegrass and clover reseed failed and a fertiliser rep advised him just to do the same again, he thought there had to be a better way.
In 2013 independent soil specialist Graham Shepherd came to Linnburn and taught the staff how they could assess all 200 paddocks on the station and Barrett analysed the results, grouping them into 10 areas.
“I’m big on spread sheets and collecting data.”
Earthworms were poor in numbers, which was “a little alarming”, so Barrett started searching the internet and sought the advice of US cover crop specialist Gabe Brown.
“He said stop sending your money to town: don’t soil test, cultivate or use fertiliser; get extremely diverse seed mixes and put them in the ground!”
And that was Barrett’s “if nothing else” advice to his audience: don’t get bogged down in the detail of soil food webs and carbon cycles; just break the monocrop, fertiliser-dependent system on a small area of the farm by sowing a diverse species mix and go from there.
“You will learn as you go.
“At Linnburn we have reduced our fertiliser spend hugely and we have more green drymatter than ever, and in places we never did, and we have more birds and worms.
“We are far from perfect [and] we have a long way to go but we are now resilient. We do not need to keep introducing inputs to maintain production.”
