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Plantain, specifically the Tonic and Agritonic cultivars, helps farmers reduce their environmental footprint by decreasing nitrate leaching without requiring major infrastructural changes. Studies show that it can reduce nitrate leaching from a dairy system by between 20-60%. The page discusses how plantain changes nitrogen cycling, which lowers nitrogen concentration in urine and partitions more nitrogen to faeces and milk. It also retains nitrogen in soil, giving plants more time to utilise it, thereby reducing nitrate leaching and nitrous oxide emissions. However, the effectiveness varies depending on the specific cultivar of plantain used.
Plantain is becoming an attractive option for farmers to reduce their environmental footprint without compromising production, requiring major changes to their farm system, or making a significant capital investment in infrastructure.
Plantain is recognised as a nitrogen leaching mitigation option by regional councils in Canterbury, Horizons and Bay of Plenty. ECan has information on how to get credit for using plantain to meet nutrient limits in areas where nutrient rules are in place. The DairyNZ Plantain Visual Assessment Guide and the Plantain Cultivar Evaluation System are available for meeting regional council requirements. Contact your regional council for further information.
Plantain, specifically the cultivars Tonic and Agritonic (marketed as a blend as Ecotain™) have consistently shown reduced nitrate leaching through the Forages for Reduced Nitrate Leaching and Greener Pastures projects, and research now continues via the Plantain Potency and Practice Programme. Research at Massey University and through the NZ Agricultural Greenhouse Gas Research Centre has also shown potential for Ecotain™ plantain to reduce both nitrous oxide and methane emissions.
The amount of leaching reduction achieved will depend on the soil, climate, and farm system setup.
After its first two years, a Plantain Potency and Practice farmlet experiment located at Massey University in Palmerston North has shown it is possible to reduce nitrate leaching from a dairy system by between 20 and 60% from pastures containing 30-50% plantain (cv. Agritonic). Early results from a second study at Lincoln University in Canterbury on lighter soils under irrigation, is showing similar trends to the Massey site, with a 38-50% reduction in nitrate leaching from 24% plantain pasture for the 2022 season to date. This is an exciting result, though requires confirmation with more data.
When modelled in Overseer, farmers can expect approximately 7-20% reductions in nitrate leaching for a farm containing 30% plantain. The magnitude of these modelled reductions is expected to increase when the full effect of plantain is accounted for in Overseer, following the completion of the current research programme. See the section below on Plantain in Overseer FM for further details.
Figure 1. Nitrate leaching from ryegrass/white clover (RGWC) and Ryegrass/white clover/plantain pastures with varying levels of plantain (PL) in a dairy system at Massey University. Note the higher level of leaching in 2021 is due to higher rainfall. Also note, due to supplementary feeding, the % of plantain in the diet in this system was lower than the figures presented (around 20% for the 30%PL and 30% for the two higher plantain treatments).
Several regional councils require farmers to show evidence of achieving their consented N loss limits. Plantain is one tool that can help farmers do this and DairyNZ has been asked to provide guidance on which cultivars have been shown to be effective at reducing N leaching.
To date, virtually all published evidence of the effectiveness of plantain for reducing nitrate leaching has used the Ceres Tonic or Agritonic cultivars of plantain. Agritonic is marketed by Agricom as Ecotain™, while Ceres Tonic is no longer commercially available. There is evidence of variation between different cultivars for some of the drivers of N leaching described below2,3.
A new DairyNZ-led Evaluation System is available for assessing the effectiveness of cultivars for changing N cycling in a way expected to reduce N leaching. This Evaluation System is being developed further to simplify the assessment process.
DairyNZ recommends that cultivars of plantain should meet the Effective standards of the Evaluation System, before being recommended for N leaching reduction. See the Plantain Evaluation System page for details and the current list of Effective cultivars.
Over the past decade, research has provided strong evidence that Tonic and Agritonic plantain (referred to here for simplicity as Ecotain™) can reduce nitrate leaching and nitrous oxide emissions. The plant is thought to work in four ways as shown in Figure 2 below.
Figure 2. Nitrogen cycle and the four modes of action of Ecotain™ plantain.
When Ecotain™ is included in the diet, the number of urination events and total urine volume increases, and consequently the urinary nitrogen concentration decreases.
Animal experiments have shown that on average, urinary nitrogen concentration decreases 28% depending on the conditions and the proportion of Ecotain™ in the diet9. The reason for the increase in urine volume is, at least in part, due to increased water consumption. Ecotain™ has on average around 30% lower dry matter content than perennial ryegrass6. Where Ecotain™ makes up more than 30% of the diet, water intake through the feed alone exceeds animal requirements7.
There may be other factors contributing to the diuretic effect of plantain. These are being investigated as part of the Plantain Potency and Practice Programme.
Nitrogen consumed by ruminants is partitioned into different pools including milk, faeces, and urine. The portions of N in each output increase or decrease depending on the diet. When Ecotain™ plantain is included in a cow’s diet, the portion of nitrogen intake partitioned to urine decreases, and the amount partitioned to faeces and milk increases when compared to perennial ryegrass7,5.
Figure 3. Proportion of N partitioned to urine, faeces and milk under different levels of plantain in the diet.
The following modes of action may contribute to the partitioning effect:
Lower soluble N, and rumen degradable protein (RDP) and higher rumen undegradable protein (RUP) in Ecotain™ than in perennial ryegrass. Soluble and degradable N are quickly converted to ammonia when digested and when ammonia exceeds what can be used immediately by the rumen microbes it is absorbed into the blood and excreted as N in urine. RUP passes through the digestive tract and can be metabolised or excreted as faeces.
Differences in the ratio of dietary N to non-structural carbohydrates (NSC). Ecotain™ has less structural carbohydrates (measured as neutral detergent fibre, NDF) and more NSC than perennial ryegrass. NSC are an important source of energy for rumen microbes to turn dietary N into microbial N that the cow can use to make product (meat/milk). Where the ratio between NSC and total N intake is increased, more N will be partitioned to faeces compared to urine.
The effect of plant secondary compounds found in Ecotain™ to reduce ammonia production during rumen fermentation, and therefore potentially reduce N excretion via urine.
The Plantain Potency and Practice programme is working to understand more about these processes and account for their contribution to reducing N loss.
Research using lysimeters has shown that Ecotain™ plantain can retain nitrogen in the soil, providing plants with more time to use the excess nitrogen in a urine patch, and reducing loss via leaching and nitrous oxide gas.
Lysimeter studies in the Forages for Reduced Nitrate Leaching programme showed that nitrate leaching from urine patches was significantly reduced (70-80%) under Ecotain™, even when the urine was from cows grazing ryegrass/clover pastures1. This is thought to occur due to root exudation of plant secondary compounds that slow the rate of conversion of ammonium to the more soluble and unstable nitrate, effectively giving the pasture more time to use nitrogen before it is lost to leaching or as gas.
This effect may be further enhanced with the addition of urine from cattle or sheep grazing Ecotain™ that also inhibits nitrification in soil3,4,10 (the indirect N retention effect).
These two soil effects are currently not reflected in Overseer (which predicts leaching) but research suggests their effects are potentially large. The Plantain Potency and Practice Programme is working towards understanding how these soil mechanisms work, and the extent of the effects under different levels of Ecotain™ and in different soil types/environments.
Two studies have shown reduced drainage of water below the root zone under Ecotain™ pastures, and this is another potential contributing mechanism to reduced leaching1,13.
The total effect of the proposed four modes of action of Ecotain™ plantain cannot yet be simulated in models. However, it is possible to estimate the effect of reduced N concentration in the urine patch through dilution, and reduced urinary nitrogen excretion via partitioning, using available data sets. Modifications to Overseer FM have been made to accommodate these effects11 as described below. The N retention effects will be added to Overseer when the research data is available, and this will likely increase the modelled N loss reduction.
Work is currently underway in the Plaintain Potency and Practice Programme to model the full effect of plantain in Overseer.
In the standard Overseer calculation, the proportion of N partitioned to urine = 30 + 11.9 multiplied by the %N in the feed. To accommodate the plantain effect on partitioning, this equation is adjusted on a sliding scale. For a sward rich in plantain (over 60%), the Overseer value is multiplied by 0.8. For a sward with 30% plantain, the Overseer value is multiplied by 0.9.
The dilution effect in Overseer is dealt with in terms of urine patch N load. For a standard pasture, urine patch N load is 750 kg N/ha. This is adjusted for plantain pastures on a linear sliding scale, where the N load of pastures with over 60% plantain is 450 kg N/ha and for pastures with 0% plantain is 750 kg N/ha. The dilution effect has a greater impact on reducing N loss than the partitioning effect.
As with any practice, the N leaching reduction predicted by Overseer FM at the block or farm scale as a result of including Ecotain™ will depend on a number of factors e.g., the amount of Ecotain™ in individual paddocks, the proportion of the farm sown to Ecotain™, the proportion of pasture in the diet, and the starting N loss.
The graphs below show several runs of OverseerFM on case study farms in the Lower North Island (Tararua district) and Canterbury. The range in N loss reduction from these runs is between 2.4% and 8.7% for every 10% of the pasture consisting of Ecotain™.
Figure 4. N loss predictions from Overseer at 0 to 30% of plantain for 5 case study farms in Canterbury (Hedley unpublished).
Figure 5. N loss predictions from Overseer at different levels of plantain for 5 case study farms in the Tararua district (Hedley unpublished).
Plantain has been shown to reduce nitrous oxide (N2O) emissions from the urine patch by 53% in pastures with 30% plantain (Agritonic cultivar)1,2. This finding is from two experiments (below). More work is currently underway to provide a greater understanding of the potential for plantain to reduce N2O emissions.
The 53% reduction in N2O emissions was achieved when urine was applied from cows grazing 30% Ecotain™ pastures. The nitrogen content in the Ecotain™ urine was equivalent to 750 kg N/ha, while the ryegrass/clover control was equivalent to 1000 kg N/ha (Figure 6).
In a second experiment, urine from cows grazing ryegrass/clover pastures was applied to all treatments and was equivalent to 610 kg N/ha. This experiment also showed a reduction in N2O emissions from Ecotain™ pastures. This indicates that the soil N retention effect described above (in relation to leaching) is also likely to work for reducing N2O emissions.
Other work looking at the effectiveness of plantain for reducing N2O emissions is ongoing at Massey University and as part of the NZ Agricultural Greenhouse Gas Research Centre. More data is required before N2O emissions reduction from plantain can be included in models such as Overseer.
Two studies have been conducted to investigate the effect of plantain on methane emissions, but more data is required to confirm any benefit. The first study15 showed that methane yield increased in heifers fed diets including plantain due to increased dry matter intake, but methane production per unit of dry matter eaten was reduced by 30% with 45% plantain in the diet. In a second study16, methane emissions per unit dry matter intake were lower for cows fed 100% plantain compared to ryegrass. This was largely explained by a lower digestibility (feed quality) of the plantain in this experiment compared to ryegrass.