What the research says
Plantain, specifically Ecotain™, has 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 emissions and methane.
What N leaching reductions you could expect
Experiments located at Massey University in Palmerston North have shown it is possible to reduce nitrate leaching by between 20 and 60% from pastures containing 30-50% Ecotain™ plantain. The amount of leaching reduction from Ecotain™ will depend on the soil, climate, and farm system setup.
Why Ecotain™?
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. These cultivars are marketed by Agricom as Ecotain™. There is evidence of variation in the effectiveness of different cultivars for some of the drivers of N leaching described below2,3. A new Evaluation System is available for assessing the effectiveness of cultivars for achieving reduced nitrate leaching. DairyNZ recommends that cultivars of plantain should meet the standards of this Evaluation System, before being recommended for environmental purposes.
How Ecotain™ plantain reduces nitrate leaching
Over the past decade, research has provided strong evidence that Ecotain™ plantain can reduce nitrate leaching and nitrous oxide emissions. The plant is thought to work in four ways as shown in Figure 1 below.
Figure 1: Nitrogen cycle and the four modes of action of Ecotain™ plantain.
Action #1: Dilution effect
When Ecotain™ is included in the diet, the number of urination events and total urine volume increases, and consequently the urinary nitrogen concentration decreases.
Action #2: Partitioning effect
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.
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Figure 2. 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, 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 fermentation8, and therefore potentially reduce N excretion via urine.
The Plantain Potency and Practice programme is working to understand more about these processes.
Actions #3 and 4: Direct and indirect N retention effects
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.
Plantain in Overseer FM
The total effect of Ecotain™ plantain cannot yet be predicted 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 therefore been possible to accommodate these effects11 as described below. The N retention effects will be added to Overseer when the required data is available, and this will likely increase the magnitude of 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.
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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™.
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N loss predictions from Overseer at different levels of plantain for 5 case study farms in Canterbury (Hedley unpublished).
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N loss predictions from Overseer at different levels of plantain for 5 case study farms in the Tararua district (Hedley unpublished).
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Can plantain have an effect on my GHG emissions too?
Plantain has been shown to reduce nitrous oxide (N2O) emissions from the urine patch by 53% in pastures with 30% Ecotain™1,2. This finding is from one experiment. More work is currently underway to provide a greater understanding of the potential for plantain to reduce N2O emissions.
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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 4).
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.
Figure 4: N2O emissions from urine patches with urine applied from cows grazing different proportions of plantain in the Waikato (A) and cows grazing perennial ryegrass/clover pastures in Southland (B), ref.12
