Lessons on reseeding from Moorepark

Glyphosate, or Roundup as it is commonly known, is in the news a lot lately. Various lawsuits have been filed in the US against the manufacturer on health grounds. Some EU countries have banned the use of Roundup in crops used for agriculture. Farmers are rightly worried as Roundup is an effective weed killer.

In the grassland scene, farmers mostly use Roundup during the reseeding process – to kill off the old sward before cultivating. But just how important is Roundup in the reseeding process? While not designed to answer that question, the reseeding demonstration at the Moorepark open day gave us a clue.

At the 2017 open day, 0.25ac plots of recently reseeded fields were on display. The plots were all reseeded with the same variety earlier in the year. One plot was sprayed with Roundup and post-emergence spray and another was not sprayed at all. The appearance of the sward or, more importantly, the appearance of weeds was not too dissimilar between the plots but there were docks appearing in the unsprayed section.

Cleverly, the researchers at Moorepark decided to leave the plots as they were. The wires were taken down and they were managed as part of the rest of the field for 2017 and 2019. Then, in preparation for the 2019 open day which took place in early July, the reseeding plots were replicated and the wires were put back up around the 2017 plots.

The difference between the sections is unbelievable. The unsprayed section from 2017 is now a mass of weeds, mostly docks. The sprayed section from 2017 is still clean, with no docks visible. However, because the 2017 demo looked at both Roundup and post-emergence spray together, it’s hard to say whether it was the Roundup, or the post-emergence spray that caused the sprayed sward to be so clean.

I think it is absolutely vital that the post-emergence spray is applied

The demo carried out this year has extra treatments, breaking it down into Roundup only, post-emergence spray only, no spray and both Roundup and post-emergence spray. From looking at these treatments, albeit only a few weeks after sowing, you would say that the post-emergence spray has the bigger benefit in terms of weed control compared with the Roundup-only treatment. However, it is early days yet.

“I think it is absolutely vital that the post-emergence spray is applied. If you have a relatively clean sward with not too many docks and not much scutch, etc, you might get away without Roundup if everything else is done well and post-emergence spray goes out at the right time.

“We haven’t done an experiment looking at this issue though,” says Teagasc researcher Deirdre Hennessy.

Obviously, cost comes into the equation too and many farmers decide not to do a post-emergence spray as it adds cost to the reseeding job, both in terms of the chemical cost and the contractor cost of spraying.

At the Moorepark open day, the full cost of reseeding with both Roundup and post-emergence spray was put at €799/ha. The full cost of no Roundup but post-emergence spray was put at €724/ha, a saving of €75/ha. The costs were the same for Roundup but no post-emergence spray at €724/ha. The cheapest option, not spraying at all, worked out at €660/ha.

Farmers will have to wait until the 2021 open day to see the difference between the 2019 reseeding treatments. It should be noted that this was only a demonstration and not a controlled experiment on the efficacy of spraying treatments.

Over the four years of the study from 2014 to 2017, the inclusion of clover in the sward improved milk solids yield per cow by 48kg, increased grass growth by 1.2t/ha and increased overall profitability by €305/ha. However, the range in performance differed between the years as the rate of clover in the sward reduced over time.

In 2014, there was 37% clover in the swards, this was down to 25% for 2015, 18% for 2016 and 15% for 2017. Increases in milk yield and grass growth declined in each year of the experiment as the percentage of clover declined. There was no difference observed in grass ploidy, so tetraploids and diploids had similar milk production and clover content characteristics.

Importantly, both the grass-only and grass clover treatments were on the same level of nitrogen fertiliser at 250kgN/ha.

Next study

In the next study, set to run from 2019 to 2021, the researchers will be looking at the effect of different levels of chemical nitrogen (150kgN/ha v 250kgN/ha).

A concerted effort will be made to keep the clover in the swards at optimum levels through over-sowing of white clover and reseeding. The optimum level in the sward is set to be 20% to 25% clover.

Milk yield

At the Moorepark open day on 3 July, the cows on the grass-clover sward at 150kgN/ha were milking 1.70kgMS/cow, while those on grass-only swards at 250kgN/ha were milking 1.59kgMS/cow, while on the same level of concentrate feeding and pre-grazing yields were the same at 1,400kgDM/ha.

Curtin’s – the systems research farm at Moorepark – is trying out multi-species swards. The mixed sward contains red and white clover, perennial ryegrass, chicory, plantain and timothy. One of the 17 blocks of paddocks at Curtin’s was sown down to multi-species swards in 2018.

Farm manager Caroline O’Sullivan is managing these swards more or less the same as other swards on the farm, with the exception of fertiliser use. The multi-species block, along with other high clover paddocks, are on a half rate of nitrogen during the summer months. So instead of getting the standard 250kgN/ha as per most of the farm, these paddocks are getting closer to 150kgN/ha over the course of the year.

The Irish Farmers Journal walked through the multi-species sward last week. There are six paddocks within the block – one paddock for each of the six treatments on the farm. Caroline had four of the six paddocks closed up for silage. The other two paddocks were grazed about two weeks ago.

The rationale behind multi-species swards is that they are more diverse and have different strengths and weaknesses so they complement each other.

Plantain has also been shown to reduce the nitrogen content in urine

For example, clover is highly digestible and fixes nitrogen. Timothy has good early spring growth. Chicory and plantain are two herbs that are high in minerals and are fairly resistant to drought.

Plantain has also been shown to reduce the nitrogen content in urine. Each of the species have different rooting depths so they improve drainage and soil diversity also. With different flowering stages the multi-species swards provide more food for insects.

However, when I visited the site, I was disappointed with what I saw. The swards looked hungry and open and there appeared to be a high level of stemmy grass and fibre material in the sward. Perhaps it was just a time of year issue, but everything looked a bit stressed. We will report on this further at the end of the year.

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