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In 10: New N loss research shows lower amount of plantain still makes big impact

• DairyNZ

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Can a small amount of plantain in pasture really reduce nitrogen loss on-farm? New research from trials at Lincoln and Massey Universities suggests it can, and the results might surprise you. Kate Fransen shares the latest findings from DairyNZ’s Plantain Potency and Practice Programme and an update on what’s working, how farmers are using it effectively, and what’s next for the programme. 

Find out more about this research programme: Plantain Potency and Practice Programme - DairyNZ | DairyNZ 

Read the latest news story on this research: Latest plantain trial results again show role in reducing nitrogen leaching | DairyNZ 

Have feedback or ideas for future episodes? Email us at talkingdairy@dairynz.co.nz

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Jac McGowan:

Kia ora and welcome to Talking Dairy in 10. I'm your host, jack McGowan from DairyNZ. Today we've got an interesting update about our research into reducing nitrogen loss from plantain use in pasture. This project has just finished its fourth year and new trial results show that even a little plantain can make a real difference. Joining us today is Kate Franson, who leads the DairyNZ Plantain Potency and Practice Programme, which is jointly funded by DairyNZ Ministry for Primary Industries through the Primary Growth Sector Fund, pgg Rights and Seeds and Fonterra. Kate, it's so great to have you here. Thanks, jack. Cutting straight to the chase, kate, you've got the latest trial results in from Lincoln and Massey. What did they show?

Kate Fransen:

Well, at our Lincoln University Research Dairy Farm trial over three years we measured nitrogen leaching from ryegrass clover pastures with and without plantain. To measure the leaching we've used suction cups, which are little ceramic cups with little tubes in them that we're able to measure the nitrogen in water as it goes towards the groundwater, and they're installed under each of the paddocks. The proportion of plantain in the sward was lower than what we were targeting. We had an average of 17% and it ranged from 12% to 25% through the three years of the trial. But it's been pleasing to see that even at those lower levels we've still had a large reduction in leaching. So nitrate leaching from the pastures with plantain was 26% lower than the ryegrass clover treatment. The results from our Massey side have been pretty similar. So they've also had a 26% reduction in leaching from a treatment with 25% plantain. So it's really encouraging results, jack.

Jac McGowan:

Why did you end up with a lower percentage of plantain than you were hoping for in Canterbury?

Kate Fransen:

Yeah, so plantain's been challenging to maintain in pastures. So we know that plantain lasts about two to three years now. It's not a long-term perennial. So while it started out at around sort of 30%, it gradually declines and so we've been topping it up in the pastures using some undersowing and oversewing of the pasture swords with plantain seed and that's sort of the levels that we've been able to maintain, around that average 17%.

Jac McGowan:

So you said that in both locations you had a 26% reduction in N-leaching. How did that compare to modelled predictions?

Kate Fransen:

Yeah. So our overseer model currently accounts for the effect of plantain on nitrogen levels in the urine patch. We call that the animal effect. On average this gives around a 0.6% reduction in leaching for every 1% plantain. So if we look at our results from Lincoln, with our 17% plantain, that would have accounted for around 10% reduction in leaching, whereas our measurements showed an average of 26% reduction. Okay, so what's accounting for that extra 16 odd percent? Well, we know from our lysimeter and nitrous oxide trials that have been done in the past that plantain can further reduce leaching through mechanisms that are going on in the soil. So we know that there's reduced drainage under plantain, so less water going below the root zone, which then takes less nitrogen with it. And we also know that there's a slowing of the conversion of ammonium, which is sort of the stable form of nitrogen, to nitrate, which is the stuff that leaches. So our research is currently really focused on understanding and quantifying those mechanisms with the aim of the full effect of plantain being reflected in that overseer model.

Jac McGowan:

Right. So it sounds, based on that, like there's been a shift in thinking around how much plantain is needed in pasture to achieve a large reduction in nitrogen leaching. What's the new insight and how achievable is that on farm?

Kate Fransen:

Yeah, so there was an early animal trial on plantain which concluded that you need 30% plantain in a pasture s ward to have this statistically significant effect on urinary nitrogen. So that was an animal trial run in a metabolism stall facility. But our more recent research is showing these sizable reductions in leaching at levels as low as 12% as an average across a farm. Now our plantain partner farmers we've got about 20, up to 25 at times throughout the program partner farmers across New Zealand and they're showing that 10 to 20% plantain is an achievable target. That's what they're achieving at the moment across their farms.

Jac McGowan:

Okay, so you're already working with farmers that are making it work. What are some of the successful approaches you're seeing across regions?

Kate Fransen:

Yeah. So some of the examples in Rotorua where farmers are using ecotain plantain to meet their nitrogen leaching limits. They're achieving up to 20% across their farms just through broadcasting two to three kilos of seed each year with their annual phosphorus fertiliser. They do this by either adding the seed into the top of the fertiliser truck or spinning it on with a fertiliser spreader. Prillcoat seed is often used to increase the weight of the seed and help give it a more even spread. As it spins out of the fertiliser truck, the increased weight means that you need to double the seeding rate. So to get three kilos of seed you need to spread six kilos per hectare of prillcoat. Right yeah, broadcasting works particularly well in Rotorua, from what we've seen, where pasture swathes are a bit more open on those light volcanic soils over there. Moving to Southland farmers are regrassing in Southland about every seven years and they're maintaining around eight to 10% plantain across their farms just by including it in the re-grassing mix about three kilos per hectare. Plantain's a pretty small seed, so it's important that you don't sow it too deep, and some of these Southland farmers have had particular success where they've prepared the seed bed by cultivation and they're just using a roller drill, so dropping the seed on the surface and rolling over it. And that's just using a roller drill, so dropping the seed on the surface and rolling over it, and that's been really successful in getting quite high percentages of plantain.

Kate Fransen:

The proportion of plantain in new grass paddocks, pretty universally across New Zealand we're seeing around 20 to 40%, up to 50% after around six to 12 months.

Kate Fransen:

It's not a long-term perennial like ryegrass, so it's lasting two to three years in pastures before it starts to decline.

Kate Fransen:

So these farmers in Southland, similar to what I talked about with our LURDF site, lincoln University Research Dairy site, they're currently trialing broadcasting seed to top up those paddocks that they've sown and also just broadcasting across the whole farm to see if they can get plantain established that way. Lastly, in Canterbury farmers are able to maintain around 10% plantain and up to 15% plantain across their farms through a combination of including it in their regrassing mix and broadcasting quite low rates in Canterbury, around one to two kilos per hectare of seed across the whole farm with fertiliser each year. And in Canterbury we found once again, broadcasting does work best where the swords are a bit more open. This year some of our Canterbury farmers are increasing their seeding rate when they're broadcasting just to see if that gives them some higher percentage in those broadcasted paddocks. So that gives you a bit of an idea, jack, as to sort of the different things that are going on around the country and the sort of rates that we're getting hopefully.

Jac McGowan:

Yeah, cool, Thank you, Kate. Now looking ahead what's next for this programme?

Kate Fransen:

Well, now that we're confident that plantain is an effective tool for reducing leaching, we're turning our attention to adoption in nitrogen-sensitive catchments. So some examples of catchments we're working closely with at the moment are Edendale in Southland, amuri in North Canterbury, waikakahi in South Canterbury, rotorua Lake and Upper Waikato. In a few of these catchments we're hoping to measure the effect of plantain adoption on nitrogen in groundwater and streams. Some of these catchments, like Muri and Waikakehi in particular, are quite unique because they've got sort of hydrologically isolated so we can measure all of the groundwater coming off them and see what the mitigations like plantain are doing directly to that groundwater and in the streams.

Kate Fransen:

As mentioned earlier, we're also looking to further understand how plantain works in the soil so the full effect can be quantified in the overseer model. That's a huge focus for our program at the moment. And finally, agritonic plantain, which is the cultivar marketed as Ecotain, is what we've used in our trials. So we're really confident that that cultivar works to reduce nitrogen leaching. What we're now doing is looking to roll out a plantain cultivar evaluation system which aims to provide confidence in the use of a range of plantain cultivars for reducing nitrate leaching and we're hoping that future research may also help us to include other species, like chicory, into our evaluation system as well. So, yeah, those are the key focuses for the program for the next couple of years, jack.

Jac McGowan:

You talked about the different methods of maintaining plantain in the sward or increasing the amount of plantain in the sward that you were seeing being successful in different regions. Where can farmers find that information?

Kate Fransen:

So there's some basic information on our website. So look for the plantain page on our website and you'll find some information there. There's a more detailed page on our website specifically about the Plantain program and some of the results that we've been getting. You'll see some links there also to some of our farmer case studies. We're increasing the amount of case studies at the moment on our website, so there's more examples available.

Jac McGowan:

Brilliant Thanks, kate. And thanks so much for joining us on this episode of Talking Dairy in 10. If you'd like to know more, we'll link to more information in the show notes. Thanks for tuning into this episode of Talking Dairy. Make sure to hit follow so you can keep up to date with our latest episodes. You can also keep up with Dairy NZ News on Facebook, instagram and LinkedIn, or go to our website and sign up for our fortnightly Dairy NZ News emails. As always, if you have any feedback on this podcast or have some ideas for future topics or guests to have on the show, please email us at talkingdairy at dairynzconz Mā te wā mauri ora. Catch you next time.