By: Anne Lee

Only a few months into a large-scale research trial on plantain and its abilities to lower nitrate leaching, Lincoln University scientists are already working on answering the new questions arising from the trial.

Lincoln University professor of livestock production Pablo Gregorini says the farm systems trial at the university’s Ashley Dene Research and Development Station involving 273 cows aims to not only measure numerous production and environmental metrics but learn how to best manage pastures with plantain in them.

It’s comparing two rates of nitrogen fertiliser, different stocking rates and different pasture mixes – one containing a 50% plantain and 50% ryegrass white clover mix and recording when and how much supplement is fed, daily milk production, milk composition, monthly body condition score, weekly pasture covers, pasture quality information and nitrogen concentration in urine, faeces and milk urea.

Lysimeters are also being used to measure nitrogen concentrations in drainage water.

There are 80 cows on each of the lower stocking rate (three cows/ha), lower nitrogen (150kg N/ha/year) blocks and 113 cows on the higher stocking rate (five cows/ha), higher nitrogen (300kg N/ha/year) treatment.

Gregorini says the large-scale system trial builds on the component studies already carried out at Lincoln, much of it through the Forages for Reduced Nitrate Leaching study.

This new Lincoln University study is in its first season and the expectation is information will be gathered over at least two years.

Along with the cows on the farmlets it’s incorporating the use of computer model technology.

Gregorini was the lead developer of a complex cow computer model named Mindy (named after Gregorini’s wife) during his time at DairyNZ.

He’s used Mindy to help set up the trial design and has more recently used it in a study with Lincoln University professor of dairy production and dean of the university’s agriculture and life sciences department Grant Edwards.

That soon-to-be-published study, has sought to answer some of the questions already arising from the farm systems research after scientists and the farm’s management noticed differences in milksolids levels.

“We asked Mindy, what if we feed you plantain every other day or every five days or even every 10 days?

“Then we asked what if we feed you plantain at those frequencies, but we feed it to you after morning milking or after the afternoon milking?”

“We took it further and said ok what will happen if we feed you at those times and plantain makes up 25% of your diet or 50% of your diet?”

The complexity of Mindy means that she can answer those questions not only in terms of what it will do to her milk production but how it will affect her urinary nitrogen concentration and other outputs.

“What we’re doing with this kind of modelling is to take the science we’re doing now, using the resources and information we already have, and find the answers to more questions – to squeeze the orange a bit more.

“Long story short is that the modelling shows we can explain a significant amount of the variability in milk production by looking at the timing and frequency of when and how much plantain is fed.

“So it’s not just about the amount of plantain we are feeding it’s also about when we are grazing it,” Gregorini says.

The system trial and the modelling are bringing together what he calls the technology of inputs and the technology of processes in that the studies are investigating the input itself, namely the plantain and its effects, as well as the processes involved in feeding it – the when and how much.

Armed with that sort of information the next step for the scientists is to then test the model with the real thing.

So watch this space to see where the science goes next.

Gregorini says some exciting projects are already lined up for this year.

As far as the farm systems trial results go he says to date they’ve found the plantain was slower in terms of pasture growth rate in the spring so more supplement was fed early and by mid-December cows grazing the 50% plantain, 50% ryegrass white clover block had still used more supplement per cow than the cows grazing at a similar stocking rate on the ryegrass white clover only pasture with the similar (150kg N/ha/year) nitrogen inputs.

But cows on the plantain mix pasture had produced more milk than the other two treatments on a per-cow basis even though the higher stocking rate treatment had been fed more supplement than cows on the plantain mix sward.

It’s still very early days for the trial but while the full season’s information will be important the differences through the season are just as important from a practical farm management and environmental perspective.

Our land, our water 

Lincoln University’s Ashely Dene Research and Development Station is home to a detailed study on the interactions between soil, plant and animal microbiomes as part of the larger, national science challenge project, Our Land Our Water. Gregorini is Lincoln University’s principal investigator for the project and explains that the detailed Gaining Ground study is more specifically looking at understanding the interactions between soil, plant and animal microbiomes so as to help drive sustainable pastoral productivity.

A team of researchers from Lincoln University, AgResearch, Landcare Research and Otago University are using a small number of cows out of the farm systems trial to look more deeply at what’s going on with the microbiomes at different annual nitrogen fertiliser rates.

Gregorini says the hypothesis is that the use of nitrogen in a ryegrass white clover production system is controlled by the composition, activity and soil, plant and animal microbiomes interaction mediating nitrogen transactions.

Over two periods of 10 days through the season – one in November and one later in the season 10 cows from each group in the farm systems trial were split into two smaller groups of five and run on three different areas, each ryegrass white clover but with different rates of nitrogen fertiliser.

Gregorini says cows are grazed on areas with fertiliser application rates of either zero, 150 or 300kg N/ha/year.

Measures taken over those 10 days will look at pasture production, milk production and milk composition with detailed sampling on milk urea nitrogen, urinary nitrogen and faecal nitrogen.

Lysimeter data will also be used to complete the nitrogen balance. All of that information will flow through to DairyNZ senior scientist Pierre Beukes and his team to carry out whole farm modelling.

From those 10-day samples of information he will be able to develop a whole season, whole farm model that will provide a greater farm system view of what effect the three nitrogen rates have.

Gregorini says soil, plant and rumen DNA and RNA extractions will be taken and rumen samples from all of the animals will be analysed to look at not just what bacteria and other organisms are present but also how many there are, what their activity is and how they may be interacting.

The study will help build the larger picture and understanding of what is happening within farm systems and how common farm practices can be influencing different aspects within the whole animal, plant, soil connection.