These losses could offset the benefits of reduced leaching losses from nil or restrictive grazing systems as part of housing cows for all or part of the year, he told an investing in off-paddock facilities workshop run by DairyNZ in Morrinsville in November.
“Why have 90-day storage when you’re going to lose nitrous oxide to the atmosphere?” he asked.
“In many instances farmers need less than 90-day storage to satisfy regional councils. They don’t care about nitrogen (N) in the atmosphere. It’s your loss, not theirs.”
Smeaton, a contractor for DairyNZ, said Overseer estimated losses of nitrogen and phosphorus with the second being moderately manageable with riparian strips and good effluent management. But these control measures had little influence on nitrogen leaching, which in the nitrate form was highly mobile. Soils leaked nitrogen vertically with the amount being defined by how much was present, pasture growth and rainfall.
“When cows urinate they typically drop 500-1000kg N/ha in one spot,” he said.
“Ryegrass cannot use all this.”
But algae in waterways loved nitrogen and in wet soils it caused greenhouse gas emissions.
“So standing animals off on an impermeable surface sounds like a good idea,” he said.
To a degree this was true with the idea being that nitrogen would be captured and applied evenly during low-risk periods such as spring.
DairyNZ data showed that with cows off pasture all year there was a 55-65% reduction in nitrogen leaching but total nitrogen losses increased by 10-35%. If cows were off pasture for five months during autumn and winter these losses were reduced to 35-55% and total nitrogen losses were cut from 10% to 5%. If the cows were in barns instead of on crop in winter the reduction in nitrogen leaching could drop to 25%, the same as if in Waikato they were on-off grazed in winter. With restricted grazing for three hours then being stood off for 21 hours in Southland during March, April and May a 41% reduction was measured over a six-month period.
Smeaton said restricted grazing had a disproportionately large effect because it targeted the high risk period of late summer and autumn but this could vary because of rainfall patterns. Urinary nitrogen deposited in autumn was leached out over winter because of higher rainfall and lower evapotranspiration which contributed to more drainage. Lower temperatures meant pastures grew more slowly, using less nitrogen.
It was logical to think that the even return of dung and urine would improve pasture growth but with normal grazing only 30% of a paddock was covered in a year.
“This is good for clover and farmers want it because it’s a cheap source of nitrogen,” he said.
The 30% of coverage grew 50% of the drymatter produced. Modelling based on even recycling showed predicted benefits from no grazing of growth rate increases of 20% but in restricted systems this was reduced to between 2% and 8%.
‘In many instances farmers need less than 90-day storage to satisfy regional councils. They don’t care about nitrogen in the atmosphere.’
However, results of recent field work at Massey University which Smeaton described as curious showed that in the first two years pasture growth was reduced when cows were stood off in wet weather to reduce pugging. This was because nutrients weren’t returned until a large late summer application after some nitrogen and potassium losses had occurred. In the third and fourth years pasture yields were equal to or better than conventional grazing because effluent slurry was reapplied in spring and early summer.
Smeaton said there were potential disadvantages with nil or restrictive grazing systems which were:
• Clover, the cheapest nitrogen source, allowed low-nitrogen areas to remain competitive in the pasture sward. If conventional grazing is used clover has a competitive advantage across 70% of the paddock where it’s free of urine patches.
• Even return of dung and urine from barns and storage ponds could make clover less competitive.
• “Pasture doesn’t grow while the nitrogen is in the storage pond.”
• Increased gaseous nitrogen losses from stored and recycled effluent collected from housed animals.
• Capital and maintenance costs of barns, standoff pads and associated infrastructure had to be considered along with extra operating costs.
Smeaton said systems and farms were all different, including soil type and climate with rainfall patterns having a big effect on the size of the benefits of standing cows off pasture. And while return of effluent to pastures theoretically increased grass growth by two to 20% in practice results could range from negative to positive as it all depended on effluent return management.
While imported feed brought in nutrients which could reduce fertiliser requirements an Overseer budget was needed to check on this.
“Intensification of the farm enterprise to make the costs worthwhile can completely undo the nutrient loss gains,” he said.
“Nitrogen leaching goes back up which is pretty annoying.”
What about higher producing cows?
Farmers need to know when to stop spending money on supplements, Duncan Smeaton says.
Improved feeding of cows should make them more efficient, have better reproductive performance, be healthier, produce more milk per cow and therefore be more profitable. But he said the idea that high-producing cows were more efficient didn’t work in practice as well as it might be thought.
There were obstacles to achieving feed conversion efficiency (FCE) per cow and farm where pasture was part of the diet.
“Substitution is easily ignored but it never goes away,” he said.
The need to get high pasture utilisation and growth for maximum profit meant farmers used as much pasture as they could. But pasture wastage usually went up and quality down when pasture residuals went up.
Cows had to be encouraged to graze to the optimum residual of 1500-1700kg drymatter (DM)/ha.
“This results in higher pasture utilisation and profit but production per cow is below their capability.”
A DairyNZ stocking rate (SR) trial showed FCE loss as SR increased with the conclusion that the optimum stocking rate was 3.1 cows/ha or 76kg liveweight/tonne DM which optimised profit/ha.
Although FCE/cow was best at low stocking rates FCE/farm increased with SR which didn’t affect reproductive performance although it was recommended that higher stocked farms calved later to manage feed supply.
Smeaton said he believed using off-paddock facilities to integrate high levels of supplement feeding into pasture-based dairy systems was very difficult to achieve successfully.
Common outcomes included more substitution, higher pasture residuals, lower pasture utilisation and poorer quality as well as more supplementary feed being made or paddocks being topped.
“If you use less of your feed profitability can decline.”
He suggested that less than 5% of farmers ran successful high input systems which involved:
• Relentless monitoring of feed supply and accurate pasture allocation.
• Daily control by a dedicated, knowledgeable manager.
• Flexible but disciplined use of supplements.
• Good understanding of substitution.
• Knowledge of weighted average feed costs.
• Bought-in supplements fed in low waste systems.
And he cautioned that copying of such systems across multiple farm ownership hadn’t been seen so far.
Farmers shouldn’t replace good quality pasture with supplements to balance it.
“Use supplements for energy only when pasture is deficient.”
If supplements led to high grazing residuals significant substitution should be expected so farmers should always consider total costs and benefits.
“Farmers relentlessly underestimate the cost of feeding out supplements once they hit the farm,” he said.
Substitution was often a lot worse than they thought with recent Irish research showing for every extra 1kg DM of supplement 0.6kg DM less pasture was utilised.
“In spring some farmers are feeding supplement while they’re making silage or topping,” he said.
“A lot of farmers are struggling to keep their residuals under 1700kg DM/ ha.”
Substitution varied with hungry cows substituting less than better fed animals.
“At pasture grazing residuals of more than 1500kg DM/ha it’s very hard to make a profit from feeding supplements unless they are very cheap,” he said.
“For short-term feed deficits the 5% rule works pretty well but don’t forget to include all costs in the cost of feed price.”
The break-even price for supplements such as palm kernel, grass silage and barley varied widely at different grazing residuals depending on how hungry the cows were, which drove substitution.
