Special crops are soaking up the nasties from dairy cows’ pee in an “eye-opening” farm trial which could help clean up New Zealand’s rivers and streams.
The trials on a North Canterbury dairy farm have found that early sown oats and Italian ryegrass take up excess urine deposited by winter grazing cows.
“It has reduced our footprint in terms of nitrogen leaching and we’ve got a forage there that’s capturing not just nitrogen in the soil, but carbon as well,” farmer Tom Turner said.
Urinary nitrogen can leach whenever the rain is such that water moves through the soil to groundwater.
Field operations science team leader Shane Maley has been working closely with Turner.
“We started looking at catch crops and trying to work in a system approach of supporting farmers following winter grazing and trying to have an impact on any nutrient losses potentially after those winter months,” he said.
Catch crops are cool-tolerant cereals that can be planted as quickly as possible after winter grazing.
A spader drill drilling oats in Southland at the beginning of August 2023, following winter grazed swedes. Photo / Shane Maley
Typical catch crops include oats, triticale, ryecorn, Italian ryegrass and faba beans.
“We literally started with three or four strips of oats just to see if it would actually work in the middle of winter,” Maley said.
“Would it grow? Would it take up nitrogen? And to our surprise, it did a fantastic job!”
The same site as above in November and ready for silage removal. The crop produced nine tonnes a hectare. Photo / Shane Maley
There is more nitrogen in the grass than cows can use so the excess is returned to the soil, mainly as urine.
Dairy cows can urinate up to a dozen times a day, with an average volume of two litres each time.
The average equivalent urinary nitrogen application rate is estimated to be approximately 600kg of nitrogen per hectare.
Cows at Woodstock Farm. Photo / Cosmo Kentish-Barnes
Autumn and winter are the highest risk times for nitrate leaching because of the low temperatures, slow plant uptake and higher rainfall and drainage.
“Obviously we were looking at nitrogen losses to begin with, but now we’re also showing that catch crops can actually reduce sediment losses as well,” Maley said.
Results from the trials had been eye-opening, he said.
Cows winter grazed on swedes in this paddock, prior to it being sown with catch crops. Photo / Cosmo Kentish-Barnes
“We’ve reduced sediment movement or losses on-farm by 40%.
“In terms of the catch crop, we’re between 40 and 60% of potential losses of nitrogen which those crops are picking up.”
Woodstock Farm is tucked up against the foothills just south of Oxford.
The spader drill is a game-changer for Tom Turner. Photo / Cosmo Kentish-Barnes
One of its dairy platforms is on flat irrigated land and the other is on sloping down country.
“We’re milking just under 3000 cows, along with 1000 head of young stock across 800 hectares of dairy platform and another 800 hectares of dairy support,” Turner said.
When RNZ’s Country Life visited the farm in early September, a spader drill was sowing oats and Italian ryegrass in behind a 12-tonne dry land swede crop.
A sloping paddock at Woodstock Farm that has been sown in catch crops. Photo / Cosmo Kentish-Barnes
A few years earlier, the paddock would lie fallow until November as it was too wet to get any good results from a conventional cultivator going through.
The spader drill is a rare beast in Aotearoa.
The Dutch machine is designed to work best on heavier soils with not too many stones.
Shane Maley and Tom Turner admire the spader drill's ability to sow crops on muddy ground. Photo / Cosmo Kentish-Barnes
Turner said getting catch crops in early with the spader was not only a win for the environment but also for yields.
“We’re gaining a lot of kilograms of dry matter growing in that period as opposed to being short and buying in, or just having to find other alternatives of a feed source.”
This year, he is putting 50ha into catch crops after winter grazing.
One of the major beneficiaries lives under the ground.
A farm research site in Southland showed the difference between two plots - one that had catch crops and one that did not.
The soil after harvesting the crops with deep roots had a lot more earthworm activity.
The project on Turner’s farm has finished after four years but sowing catch crops to reduce nitrogen leaching and sediment losses is catching on.
