Grassroots solution for leaching
A solution to help reduce nitrate leaching could be available at grassroots for farmers. It would involve them doing what they already do well, growing pasture, but adding plantain to the mix. Richard Rennie reports.
AS THE pastoral sector grapples with the slippery problem of diffuse nitrogen losses, part of the solution might lie close to home at a grass roots level.
The Forages for Reduced Nitrate Leaching (FRNL) programme involving DairyNZ, Foundation for Arable Research, Plant and Food, AgResearch and Lincoln University has been trialling how a wide variety of forages could enable the sector to have its grass and eat it too – by reducing nitrate leaching and improving animal production.
The work had focused on studying the ability of mixed-species pastures to increase herbage production and reduce nitrogen leaching from farm systems.
It had yielded some valuable results with species New Zealand farmers were familiar with and already capable of growing relatively well.
A key species shown to deliver positive results in pasture production, animal output and lower nitrogen losses was plantain.
It performed well across those parameters in pasture swards that contain it, perennial ryegrass and white clover.
But FRNL programme leader Ina Pinxterhuis said while the inclusion of plantain in traditional ryegrass-clover swards did have a positive effect on N loss reduction, it was not a simple, silver-bullet solution to the vexing environmental and economic issue.
“We have shown from the work that it is an option and that as a key species plantain can increase drymatter production and reduce urine nitrogen concentration.
“However we are now looking at how much you have to have to see that benefit.
“A lot of farmers have some plantain but often it is not enough as a proportion to have that effect.”
Initial indications were leading scientists to the hypothesis that at least 25% plantain was needed in a sward to have the effect research trials indicated.
“But we have to really define that percentage.”
The trials had shed some interesting and surprising results on the herb consisting of a fibrous, coarse root system and capable of producing up to 19t of drymatter a hectare a year, comparable to ryegrass’ annual yield.
Unlike chicory, it tended to persist longer and had often been touted for its ability to grow in areas where summer feed was limited.
Farmers had planted it in the past to dodge drought’s impact on ryegrasses or to benefit from its higher calcium levels and vitamin content, including vitamin K.
Pinxterhuis said thanks to different root systems and seasonal growth patterns scientists had long recognised multi-species pasture mixes would often have greater annual herbage production than the conventional ryegrass-clover pastures so common on New Zealand farms.
“And what we have found is this combination of a herb (plantain), a grass (rye) and a legume (clover) is the best blend.
“In the past we may have looked at blends with several different species within them including chicory, plantain, lucerne, prairie grass, ryegrass and so on but this trial set out to identify the specific species and their combinations that get the biggest benefits.”
Earlier work indicated the presence of specific, well-adapted and compatible species was more important than the number of species in driving N loss or uptake and herbage production.
Based off modelling using the MOLLY cow model researchers settled on four trial pasture mixes – two with perennial ryegrass and lucerne or lucerne and plantain and two with tall fescue containing the same combinations of the other species.
They found pastures with plantain resulted in 39% less urinary nitrogen concentration in cows grazing it in summer and it was also lower in spring.
Milk production was found to remain almost the same across the four different mixes.
“We found that plantain had a diuretic effect, effectively increasing the volume of urine but also diluting the N concentration.
“Being more diluted meant plants were better able to take up the N within the urine patch. However, it was only effective if plantain in the pasture was above about 25%.”
While a pure plantain sward could deliver even greater reductions, Pinxterhuis said the combination of species delivered a more sustainable feed source, with the presence of legumes helping to fix nitrogen for the grass and herb species.
“And there is the risk of losing one to a pest. For example, we already have plantain moth in the North Island.”
The next step was learning from farmers who grew plantain successfully about how they established and maintained it at higher rates in the pasture.
“We want to look at the nuts and bolts of pasture management, how farmers graze it, do they use longer rotations or leave a higher residual, do they use less fertiliser?”
Commercial monitor farmers in Canterbury were already providing valuable feedback data and researchers were keen to talk to more farmers happy to pass on their experiences with plantain from the North Island.
“We are also working with the Overseer model. You may need something in Overseer to reflect the effects of plantain more accurately.”
Pinxterhuis and her colleagues were excited by the fact plantain was a known, available and affordable option to help the industry reduce its N footprint.
“The challenge is getting that proportion in the pasture mix up and keeping it there.
“Along with using crops like winter oats to mop up N, if they improve your N efficiency and reduce your N surplus it is a win for the environment and your farm business.”
