Large and small-scale trials are testing the merits of plantain in pasture. Anne Lee reports on work under way at Massey University.
Plantain and its powers to reduce nitrate leaching have been the focus of studies at both ends of the scale spectrum at Massey University.
From the detailed effects of plant compounds and the microscopic activity in the rumen to full-scale paddock trials measuring what’s in the drainage water after a full season’s grazing by dairy cows, Massey University institute of agriculture and environment head Professor Peter Kemp and his team are looking at what’s behind plantain’s powers.
Late last year Agricom launched Ecotain – the new brand name for plantains that have the right levels of bioactive compounds to cut potential nitrate leaching.
Both Tonic plantain and AgriTonic come under the Ecotain umbrella and have proven they have the necessary attributes.
Numerous trials have found cows grazing Tonic plantain have significantly lower urinary nitrogen levels (33% less when grazing 50-50 ryegrass plantain than ryegrass white clover) and lysimeter trials have found reduced nitrate leaching under the urine patch. (Dairy Exporter, November 2017, p38-40).
Kemp says plantains are well known to have three bioactive substances in them – aucubin, acteoside and catalpol.
The comparative amounts of these appear to be important in determining whether the plantain cultivar can help reduce the amount of nitrogen in cow urine. Kemp says Massey University technician Chris Rawlingson has become an expert in extracting and analysing the compounds to the extent new cultivars in breeding programmes can now be efficiently screened to check they have the right mix.
Massey University post-doctoral researcher Dr Soledad Navarrete’s PhD study looked closely at the bioactives – their levels in Tonic plantain through two growing seasons and their effects on the production of ammonia in the rumen.
She found that while catalpol levels were almost negligible, aucubin and acteoside increased significantly through the growing season, peaking in May.
Although at similar levels in October, by January the levels of acteoside were almost 10 times that of aucubin.
The timing of the increase is a great fit for plantain’s ability to combat nitrate leaching as the level of bioactive compounds in the plant rise to coincide with the times when the risk of nitrate leaching is greatest.
Urinary nitrogen deposited over late summer and autumn has the greatest potential to be washed through the soil as nitrate because there’s both a higher chance of seasonal autumn and winter rainfall and pasture plants are growing at a slower rate so are taking up less nitrogen.
Navarrete’s second study looked at the effects of increasing amounts of acteoside and aucubin on net ammonia gas production during in vitro rumen fermentation.
Kemp explained that by measuring ammonia production it was possible to gauge how efficient digestion was.
The more ammonia the less efficient and the more likely nitrogen was being excreted in the urine.
Navarrete took rumen fluid from cows and added either chicory, which has no bioactives, or Tonic plantain, taking gas readings for the next 24 hours.
The plantain digestion produced 40% less ammonia gas than the chicory over the 24-hour period.
Navarrete also added the amount of aucubin and acteoside found in the plantain to both the chicory and plantain digestion processes.
Gas production dropped in the chicory and also dropped in the plantain.
Volatile fatty acids are produced by rumen bacteria when they digest and break down carbohydrates in plant material. They’re used as an energy source and for milk and meat production.
Navarretes’ study found acteoside helped with the production of some volatile fatty acids whereas the addition of aucubin didn’t.
However, aucubin has been implicated in the diuretic effects associated with plantain that help dilute urinary nitrogen concentrations.
Kemp says it seems both chemicals are needed in specific amounts and it may be that getting the balance of both right is particularly important.
Farm system scale study
Massey number four dairy’s impressive plumbing infrastructure set up during P21 trials is being put to good use measuring the nitrate levels in drainage under paddocks grazed by cows.
Kemp says three different pasture types are being tested:
- Ecotain only.
- Ecotain with red and white clover (50% Ecotain 50% clovers).
- Ryegrass – white clover.
Kemp says the Ecotain with red and white clover mix is one some farmers are using already, particularly in areas without irrigation as the Ecotain gives good summer production.
Five replicates of each pasture treatment have been set up with 0.8ha in each grazing plot.
Each has its own isolated drainage system which takes any drainage water to a collection point where the flow is subsampled and each sample collected daily.
The nitrogen loss in the drainage water is measured as are nitrous gas emissions and the nitrogen present in cows’ urine, dung, milk and blood.
Fonterra is also analysing the milk composition from each treatment.
Sixty cows are involved in the study and are grazed on about 1ha of each pasture treatment for five to six days to acclimatise the animals before they go on to the experimental area to graze for two days each month.
“We know what happens at an experimental level now – there have been a lot of trials carried out here and at Lincoln that are giving consistent results – but we want to see what happens in a normal grazing situation over a whole season.
“Sometimes nature can do strange things when you scale experiments up in the paddock. There can be interactions or effects we didn’t anticipate.”
Two grazings were carried out at the end of last season and drainage water collected and analysed through the winter to ensure the whole system was working as it should.
This season the trial is being run in earnest with animal data being collected along with nitrous gas emissions.
Drainage sampling will happen as drainage occurs which isn’t likely until later in autumn and through the winter.
Alongside the farmlet study nitrous oxide measures and recordings of nitrogen fractions in the soil are being measured in the non-drained area.
PhD student Jimena Rodriguez is carrying out that study using urine from cows grazing plantain.
Nitrous oxide is a potent greenhouse gas so any reductions in nitrous gas emissions could give plantain another big tick in terms of its environmental benefits.
The farmlet trial is a spinoff of work done in the Greener Pastures project funded by Callaghan Innovation.
Much of the funding for the farmlet trial is coming from Massey University with some input from Fonterra.
Kemp says the next step would be to sow one treatment in an Ecotain, ryegrass, white clover mix which farmers are already adopting.
Other studies have suggested that to get a meaningful reduction in nitrate leaching at least 30% of the pasture should be plantain.
Results from the farmlet study should be available later in the year.
