Challenging times for grasslands

by Mariecia Fraser

Most farmers are aware of the Recommended Lists of grasses, legumes and other crops – there’s usually plenty of publicity as they’re launched every couple of years.  But fewer farmers and land managers are familiar with how the testing is done. 

A standard trial format is carefully imposed across all six sites that are involved in generating the data used to create the rankings for England and Wales.  This makes sure that all the varieties being tested are treated in the same way.  However, the format used has a number of crucial limitations.  Firstly, the testing is all done at sites with excellent growing conditions in terms of soil and climate.  Secondly, rather than using real animals, grazing is ‘simulated’ by cutting with mowers every three weeks.  This means that all the material is removed at a standard height, which doesn’t represent the impact of real grazing since animals are always removing material selectively. Thirdly, the test plots all receive high application rates of nitrogen fertiliser. 

The format of the testing means that the varieties demonstrate the maximum yields they are capable of, which is the main measure they are subsequently ranked on in the Recommended Lists.  But what happens once the same grasses are expected to perform in less than optimal growing conditions, i.e. those more typical of those found on upland farms? 

To use an analogy; how well is a Ferrari going to do on a rough old farm track?  Will it still be performing well in all conditions, or is a Landrover a safer bet long-term?

And of course, ‘grass seed’ as sown on farm is almost always made up of a combination of different varieties (e.g. a mix of different ryegrasses), and usually a combination of different plant species (e.g. a mix of different grasses and clovers).  So in real swards we have a situation where competition between plants for nutrients, light and water will mean some will thrive while others struggle.  Added to this are the effects of selective grazing, particularly by sheep – some plant species will be heavily targeted while others are largely avoided. 

Given the jump from testing to the on-farm world it’s not surprising that sward stability is almost inevitably poor, with key species being lost after only a few growing seasons.

Plus, these days productivity is just one factor that grassland is judged on.  We also need pastures to support above- and below-ground biodiversity, store as much carbon as possible, cope with dry conditions if there’s a drought, and reduce rainfall run-off when the storms come.  If subsidy schemes shift to a greater emphasis on delivery of ‘public goods’, these measures could have a much greater influence on support payments.

This is the background to a major new project on grassland mixtures that we began the experimental work for last year.  The project is part of a multi-million pound research programme at IBERS, funded by the Biotechnology and Biological Sciences Research Council (BBSRC), aimed at improving the economic, productive and environmental sustainability of crops in the face of climatic and political change.   

Plots being sown at the site 70 m above sea level at Trawscoed. This site represents very good growing conditions.

Our grassland research is testing the effects of multiple stresses on grass and legume mixtures over seasons and years, and is taking place across four sites along a ’challenge gradient’.  We have sites at altitudes of 70 m and 150 m above sea level at the university’s Trawscoed Dairy Research Centre, and sites at 230 m and 340 m above sea level at Pwllpeiran.  Detailed surveys have shown the underlying soil chemistry of the different sites are broadly similar, but that nutrient levels decline with altitude.  Weather stations are providing detailed information on the extent to which temperatures, rainfall, wind speed and other meteorological parameters also change across the gradient.

The top site, at 340 m above sea level, under snow in March this year.

At each location replicate plots of two alternative seed mixtures have been sown; both very similar to mixtures available commercially.  The first is mostly ryegrass with a modest clover component and is typical of a mix aimed at delivering consistent production of high digestibility forage across the growing season (species mix: different ryegrasses, timothy, white clover and red clover).  The second is a more diverse mixture targeted at lower input systems (species mix: different ryegrasses, timothy, meadow fescue, red fescue, meadow grass, crested dogstail, white clover, red clover and lotus).

Each plot has been split into four sub-plots which receive different management regimes; 1) continuous grazing by sheep, 2) rotational grazing by sheep, 3) 3-week cutting (i.e. ‘simulated grazing’), and 4) conservation (silage) cutting (at 6 week intervals).  All the plots were established according to best practice industry guidelines, and the managements imposed also reflect best practice.  This means that the rates of fertiliser nitrogen applied are representative of those on farm.

Plot harvesting underway.
Managements were first imposed in April and this photo was taken in July. It shows a clear difference in clover content between the ‘simulated grazing’ cut and real grazing.

Detailed measurements of the impacts of site and management regime on herbage biomass, sward height and botanical and nutritional composition are being made across seasons and years. To understand the interactions between environmental conditions, the different combinations of plant species and the management regimes imposed, the very latest DNA and molecular techniques are being used to monitor genetic shifts within plant populations as well as the impact of the grazing preferences of the stock.  This will enable us to track the way different sward components respond to varying degrees and frequencies of biomass removal.  The related impact on the nutritional value of the forage is being explored using a variety of metabolomic techniques.  All this lab work is also being complemented by the use of cutting-edge imaging technologies using multi-spectral cameras to map three-dimensional changes in the sward over time. 

Ultimately all the findings will form the basis of new approaches to developing and testing mixtures that deliver stable and persist multi-functional swards.  Results from the project will feed directly into plant breeding programmes at IBERS.

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