Cutting cow numbers not best solution to reducing leaching, says scientist

Cutting cow numbers is not necessarily the solution to dairy farms reducing their nitrogen leaching to protect waterways, a scientist says.
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A high performing central Canterbury dairy farm has shown it is possible to reduce nitrogen leaching by more than 30 per cent while maintaining cow numbers and running a high stocking rate of 4.3 cows a hectare.
Canlac Holdings equity manager Tony Coltman said farmers needed to get on board with reducing their environmental footprint and bring the community with them. «Rather than throwing stones and being negative, let’s get on and deal with it.»
Canlac, near Dunsandel, had exceeded its required nitrogen reduction target four years early while being in the top 5 per cent of dairy farms for financial performance. The 318ha farm , which milked 1367 cows at peak in the 2017-18 season, consistently produces 500 kilograms of milksolids a cow and about 2100kg of MS/ha.
Canlac had already reduced its baseline (2009 to 2013 average) nitrogen loss figure of 83kg/ha to 54kg/ha through improvements in irrigation efficiency, a reduction in nitrogen fertiliser, buying in feed with a lower nitrogen content and introducing plantain in pasture.
DairyNZ general manager new systems and competitiveness David McCall, of Hamilton, said the regional council-imposed nitrogen limits «at first sight look hefty».
Under the Canterbury Land and Water Regional Plan, dairy farmers in the Selwyn-Waihora water catchment must reduce nitrogen losses by 30 per cent by 2022. Dairy farmers in the Hinds catchment face a staged reduction of 15 per cent by 2025, 25 per cent by 2030 and 36 per cent by 2035.
Both catchments, which include intensive dairying as well as other farming, were designated by Environment Canterbury as not meeting water quality targets. Other farming types, like arable and dairy support, have lower reduction targets to meet.
Nitrogen was a key nutrient used extensively by dairy farmers to boost pasture growth, but in excessive quantities it becomes a pollutant, at risk of leaching into groundwater, rivers and streams and degrading water quality.
«I bring confidence and hope that farmers can achieve these limits based on the science we started seven years ago,» McCall told a DairyNZ field day at Canlac.
«Just tweaking our existing systems is not going to get us there.»
Dairy NZ had launched a project where it would link about 30 dairy farmers in the sensitive Selwyn-Waihora and Hinds catchments with scientists to gain knowledge and come up with practical solutions to reduce nitrogen losses, providing an example for others. What worked on one farm may not be the best option on another, McCall said.
The move comes as Greenpeace campaigns the Government to ban synthetic nitrogen fertiliser.
Greenpeace’s sustainable agriculture campaigner Gen Toop said that in New Zealand nitrogen was the driving force behind the grossly bloated dairy herd.
«Since 1990, dairy cow numbers have more than doubled. In the same period the use of synthetic nitrogen fertiliser increased seven-fold. Dairying is by far and away the biggest user,» Toop said.
McCall said stocking rate wasn’t the problem and not necessarily the solution. «It is about matching feed supply and demand, so there is no excess nitrogen kicking around the farming system when we don’t want it, in autumn and winter in Canterbury.»
To manage this, farmers needed to get rid of cull cows early, in autumn, and have a minimum stocking rate in March and April.
In terms of science, «the more nitrogen that comes on to your farm, the bigger the nitrogen surplus you will produce and the more leaching you will have».
At best, 40 to 45 per cent of this was converted into milk, with the poorest conversion on farms about 25 per cent.
In addition to fertiliser, nitrogen also arrived on farm as bought-in feed.
«If plants are taking up that nitrogen there is no problem. So matching the plant requirements with nitrogen is key. There is also the huge dollop of 500 to 700 kilograms of nitrogen that comes in a cow’s urine patch.
«In spring, plants can manage most of that, but if you combine that with plants being slow to grow in autumn and winter, or no plants, then we have a problem.»
While ryegrass and clover had a high nitrogen content, other pasture plants such as plantain which was increasingly being used by dairy farmers had a lower nitrogen concentration. As plantain had a diuretic effect on cows, this enabled a greater spread of nitrogen from urine over pasture. Plantain roots may also inhibit nitrogen from leaching into the soil profile.
High energy feeds, such as fodder beet or grain were also efficient converters of nitrogen.
DairyNZ senior developer farm systems Phillipa Hedley said a cow «doesn’t create nitrogen».
Hedley, who said she was nicknamed «Mrs N» as a farm consultant in the 1980s for advocating nitrogen to boost pasture production, said farmers had got into a system where they followed every pasture grazing round with a nitrogen fertiliser application. «The next thing you have clocked up 300kg of nitrogen a hectare.
«The challenge is to bring your nitrogen applications down while maintaining your productivity. Clover (a nitrogen fixer) will take a while to come into your system, but it will make a big difference to your profit and the environment,» Hedley said.
Coltman said the installation of a second centre pivot, replacing a less efficient irrigator and the extension of the effluent spreading area from 21 to 41 per cent of the milking platform contributed to a significant reduction in nitrogen loss in 2013. Effluent storage was increased so it could be applied when it would achieve the best growth response.
Nitrogen fertiliser applications had also been reduced from 292kg to 224kg/ha a year. «This was achieved by slowing the grazing round, requiring fewer applications, and by maintaining a relatively low rate each time of 27kg to 29kg/ha.
«The total amount of nitrogen fertiliser used was reduced, but the same amount of pasture has been harvested.»
Canlac bought feed, such as maize silage and fodder beet, with a lower nitrogen content and had introduced plantain into pasture.

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Así lo expresó Domingo Possetto, secretario de la seccional Rafaela, quien además, afirmó que a los productores «habitualmente los ignoran los gobiernos». Además, reconoció la labor de los empresarios de las firmas locales y aseguró que están «esperanzados» con la negociación entre SanCor y Adecoagro.

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