Plantain is becoming an attractive option for New Zealand dairy farmers to reduce their environmental footprint without needing to compromise milk production, make major changes to the farm system, or make a significant capital investment in infrastructure. 

We know farmers need to see evidence that plantain works and they need to understand how to implement it successfully. That evidence is building – and with it, confidence in plantain – thanks to around 10 years’ research, summarised in this article. 

Plantain, specifically the cultivars Tonic and Agritonic (marketed by Agricom as Ecotain), has been consistently shown to reduce nitrate leaching. We saw that in the Forages for Reduced Nitrate Leaching and Greener Pastures projects, and research now continues via the DairyNZ-led Sustainable Food and Fibre Futures Plantain Potency and Practice programme. Meanwhile, research at Massey University, AgResearch and the NZ Agricultural Greenhouse Gas Research Centre has also shown Ecotain plantain’s potential to reduce nitrous oxide (N₂O) emissions. 

Plantain is currently recognised as a nitrate leaching mitigation option by regional councils in Canterbury, Horizons, Southland and Bay of Plenty, where nitrate leaching limits are in place. 

What reductions can be expected?

The amount of nitrate leaching reduction you can achieve from using plantain will depend on the soil, climate, and farm system set-up. 

After its first two years, a Plantain Potency and Practice farmlet trial at Massey University, Palmerston North, has shown it is possible to reduce nitrate leaching by between 20 and 60% from grazed pastures containing 30-50% plantain (Agritonic cultivar)1 compared to traditional perennial ryegrass/white clover. Early results from a second study at Lincoln University, Canterbury, on lighter soils under irrigation, are showing similar trends. To date, there has been no difference in milk production between treatments on either farm.

How does Ecotain plantain reduce nitrate leaching?

Based on the research, it appears plantain reduces nitrate leaching via four mechanisms

Mechanism 1:

Urine dilution effect Nitrate leaching occurs due to a high concentration of nitrogen (N) in the urine patch. 

When Ecotain plantain is included in the cow’s diet, the number of urination events and total urine volume increases. Consequently, the urinary N concentration decreases. 

A meta-analysis of animal experiments showed urinary N concentration dropped, on average, by 30%, depending on the conditions and the proportion of Ecotain plantain in the diet, due to 17% greater urine volume and 22% reduced total N excretion2. Why is there an increase in urine volume? At least in part, it is because animals fed plantain ingest more water from the pasture. Ecotain has, on average, around 30% lower dry matter content than perennial ryegrass3. Where Ecotain makes up more than 30% of the diet, water intake through the feed alone exceeds animal requirements⁴.

It is possible there are other factors contributing to a diuretic effect of plantain. We are investigating these in the Plantain Potency and Practice Programme.

Mechanism 2:

Animal partitioning effect Nitrogen consumed by ruminants is partitioned into different pools, including milk, faeces and urine.

 Exactly how much N goes into each output depends on the animal’s diet. When Ecotain plantain is included in a cow’s diet, the portion of N intake partitioned to urine falls, and the amount partitioned to faeces and milk rises, compared to perennial ryegrass. That is due to a lower proportion of soluble proteins and a higher carbohydrate to protein ratio^3,4.

Mechanisms 3 and 4:

Direct and indirect soil N retention effects Research using lysimeters has shown Ecotain plantain may retain N in the soil, giving plants more time to use the excess N in a urine patch, and reducing loss via leaching and N2O emission. 

Lysimeter studies in the Forages for Reduced Nitrate Leaching programme showed nitrate leaching from urine patches was significantly reduced (70-80%) under Ecotain, even when the urine was from cows grazing ryegrass/ clover pastures5. We believe this is due to release of plant secondary compounds from the roots and litter that slow down the rate of nitrification, i.e., the conversion of ammonium to the more soluble nitrate. This effectively gives the pasture more time to use N before it’s lost from the root zone. 

This effect may be further enhanced with the addition of urine from cattle or sheep grazing Ecotain (the indirect N retention effect). Soil microcosm incubation studies showed a significant drop in the nitrification rate from urine derived from dairy heifers and sheep that grazed plantain monocultures, compared with ryegrass/clover mixtures^6,7,8. 

Currently, Overseer’s estimates of nitrate leaching do not reflect any effects on nitrification rate, but research suggests these effects are potentially large. The Plantain Potency and Practice Programme will improve our understanding of the soil mechanisms, and the extent of the effects under different proportions of Ecotain in pasture, for different soil types and climates. 

Various studies have shown there is less water drainage below the root zone under Ecotain pastures. This is another potential contributing mechanism to reduced leaching⁵.

Plantain in Overseer 

When plantain is modelled in Overseer, farmers can expect to see, on average, a 6% reduction in nitrate leaching for every 10% of plantain in the pasture. However, the estimated reduction will vary between farms. This is because of different soils and climate, and differences in use of supplements, which determine the proportion of plantain in the diet ingested. 

Currently, Overseer estimates the reduction in nitrate leaching resulting from changes to urinary N only. We expect the magnitude of these modelled reductions to increase when the soil effects of plantain are also accounted for, after the current research programme is completed. 

How plantain affects GHG emissions 

Plantain has been shown to reduce N2O emissions from the urine patch by up to 50% in pastures with 30-50% plantain (Agritonic cultivar)1 . As with nitrate leaching, the reductions were attributed to direct plant/soil effects and an indirect effect from urine from animals grazing plantain. We need to better understand the mechanisms of these effects before N2O emissions reduction from plantain can be included in models like Overseer.

Cultivar differences

Greener Pastures research provided some evidence that plantain cultivars vary in their ability to reduce nitrate leaching. Differences have been shown for urine dilution in sheep6 and nitrification inhibition properties of urine from sheep fed plantain^6,7. 

There is evidence that Tonic and Agritonic (Ecotain) plantain are effective at reducing leaching, but we need to know more about the other cultivars. As such, the Plantain Potency and Practice Programme is developing an evaluation system to test the effectiveness of other cultivars.

Initial experiments^{9, 10} showed methane emissions per kilogram of dry matter eaten fell significantly when the diet included plantain, but this was associated with either greater feed intake or lower digestibility of the feed. We need more data to better understand if plantain is an option to reduce methane emissions per kilogram of product or per hectare

Plantain pasture and milk production 

Improved plantain cultivars were originally released for greater feed availability in dry summers, to use as a short-term pure crop, or in mixedspecies pastures. This was especially successful in sheep and beef dryland systems.

More recent data from commercial dairy farms in Tararua reiterated this benefit. A 10% greater annual yield was achieved from ryegrass/plantain/clover and 13% greater yield from plantain/ clover mixtures than from the standard ryegrass/clover mixture. This was mainly achieved from greater yields in summer and autumn:

• In summer a 16% yield increase was achieved from the ryegrass/ plantain/ clover mix, and a 54% increase from a plantain/clover mix
• In autumn a 10% and 13% increase was achieved from these same mixes¹¹

The meta-analysis of animal experiments2 also showed an average increase in milk yield of 0.07kg MS/cow/day when plantain made up a proportion of the diet. That was because of a higher yield in the late lactation experiments. 

Challenges with implementation

Even though plantain has been used on New Zealand farms for decades, and its environmental benefits are promising, implementation challenges remain. 

Key challenges include establishing and maintaining target levels of plantain in mixed pasture swards; limited chemical options for control of broadleaf weeds; plantain moth and grass grub pests in some areas; and occasional palatability issues, seen primarily when rounds get longer in late autumn/winter. 

The Plantain Potency and Practice programme is further investigating methods of establishment and management to achieve and maintain meaningful plantain content in multispecies pastures. A partnership with farmers in different regions, and their local agronomists, is helping with developing more measures to control weeds and pests, aided by results from earlier plant breeding¹².

Risks and opportunities

Research in the Plantain Potency and Practice programme has confirmed milk from plantain-fed cows does not pose any risk to human health, and that there are no significant changes to gross milk composition. 

There are potential benefits, though. Milk from plantain-fed cows is higher in Omega 3, which suggests there is an opportunity for this milk to be marketed to consumers as a value-added product. 

Research continues into risks and benefits for milk products (taste, texture etc.), checking for the risk of accumulation of heavy metals (cadmium) in offal, and assessing the benefits, risks and associated management for animal health.

References

1. Navarrete, S., P. D. Kemp, J. B. Pinxterhuis, E. M. K. Minnée, and K. E. Fransen. 2023. Evidence of environmental benefits of plantain pastures. Proceedings of the XXV International Grassland Congress, Covington, Kentucky, USA.
2. Nguyen, T., S. Navarrete, D. Horne, D. Donaghy, and P. Kemp. 2022. Forage plantain (Plantago lanceolata L.): Meta-analysis quantifying the decrease in nitrogen excretion, the increase in milk production, and the changes in milk composition of dairy cows grazing pastures containing plantain. Animal Feed Science and Technology 285, 115244. https://doi.org/10.1016/j. anifeedsci.2022.115244
3. Minnée, E. M. K., B. KuhnSherlock, J. B. Pinxterhuis, and D. F. Chapman. 2019. Metaanalyses comparing nutritional composition of perennial ryegrass (Lolium perenne) and plantain (Plantago lanceolata) pastures. Journal of New Zealand Grasslands 81:117-124. https:// www.nzgajournal.org.nz/index. php/JoNZG/article/view/402/61
4. Minnée, E. M. K., C. M. T. Leach, and D. E. Dalley. 2020. Substituting a pasture-based diet with plantain (Plantago lanceolata) reduces nitrogen excreted in urine from dairy cows in late lactation. Livestock Science 239, 104093. https://doi.org/10.1016/j. livsci.2020.104093
5. Carlton, A. J., K. C. Cameron, H. J. Di, G. R. Edwards, and T. J. Clough. 2019. Nitrate leaching losses are lower from ryegrass/ white clover forages containing plantain than from ryegrass/white clover forages under different irrigation. New Zealand Journal of Agricultural Research 62:150-172. https://doi.org/10.1080/0028823 3.2018.1461659
6. Judson, H. G., P. M. Fraser, M. E. Peterson, and G. R. Edwards. 2018. Specific genotypes of plantain (Plantago lanceolata) vary in their impact on sheep urine volume and nitrification in the urine patch. Journal of New Zealand Grasslands 80:125-128.
7. Peterson, M. E., P. M. Fraser, C. R. Anderson, N. I. Joyce, and H. G. Judson. 2023. Soil nitrification inhibition with plantain (Plantago lanceolata). Proceedings of the XXV International Grassland Congress, Covington, Kentucky, USA.
8. Judson, H. G., P. M. Fraser, and M. E. Peterson. 2019. Nitrification inhibition by urine from cattle consuming Plantago lanceolata. Journal of New Zealand Grasslands 81:111-116.
9. Minnée, E., D. Dalley, M. Bryant, C. Leach, and E. Bagley. 2018. The effect of plantain in the diet of dairy cattle on methane yields and nitrogen excretion. Report prepared for NZAGRC-PGgRc. Available on request.
10. Della Rosa, M. M., E. Sandoval, D. Luo, D. Pacheco, and A. Jonker. 2022. Effect of feeding fresh forage plantain (Plantago lancelolata) or ryegrass-based pasture on methane emissions, total-tract digestibility, and rumen fermentation on nonlactating dairy cows. Journal of Dairy Science 105.
11. Dodd, M., J. B. Pinxterhuis, P. Hedley, L. Keenan, A. Duker, and A. Moorhead. 2023. Proceedings of the XXV International Grassland Congress, Covington, Kentucky, USA.
12. Box, G. M., H. G. Judson, and A. V. Stewart. 2023. The development of environmentally functional plantains. Proceedings of the XXV International Grassland Congress, Covington, Kentucky, USA.