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The role of mixed species forage in climate change mitigation and resilience

In a recent NIAB and SRUC study of the opportunities and barriers to forages for UK livestock productivity and sustainability, a wide range of currently underused forage crops and major challenges to forage production were reviewed. Some of the key themes that came through our investigations were the need to improve nitrogen use efficiency in grass and forage cropping, along with a growing interest in the use and value of mixed species swards.

This article first appeared in NIAB Landmark, issue 48, December 2021


Weather

Some of the greatest challenges to forage production identified were the prolonged wet and dry weatherspells that have been experienced more frequently in recent years. The Met Office projects that UK winters will continue to become warmer and wetter with hotter, drier summers. Summer rainfall will be less frequent but more intense, with more droughts expected. Prolonged wet weather leads to waterlogged soils which restricts root function, whilst hot, dry summers increase drought and temperature stress and stunt or stop plant growth. Baked soils have slower water infiltration rates and increased surface run off. Increased temperatures and increased CO2 content in the atmosphere mean crops will need to adapt to the new climatic conditions with greater tolerance to stressful conditions needed.

In prolonged wet weather, permanent pasture with well-developed sward bases cope best with carryinglivestock. Shorter term, youngleys will benefitfrom keeping stock off, where possible, to avoid longer term damageto soil structure and ongoing sward productivity. Prolonged dry weather will require resting grazing as much as possible, grazing swards less hard before moving on and rotating around fields or grazing blocks within larger fields.Leaving higher residueswill aid better sward survival and recovery.

Whilst perennialryegrass continues to be the most productive, relatively hardy and widespread grassland species, other species may have more of a role in the drive for climateresilience. Cocksfoot is a grass species that can become dormant in dry summers, especially useful for plant survival undersevere drought onland where this is a particular risk.Tall fescue has high water-use efficiency and a deeper, more extensive root system for endurance to summer droughtwith good spring yields in average rainfall levels.

Swards including deep rooting legumes such as sainfoin, lucerne and red clover, rigorous rooting permanent pasture grasses such as meadow fescue, cocksfoot and smooth-stalked meadow grass as well as ley grass speciestimothy, Festuloliums and herbs chicory and ribwort plantain (ribgrass) will be most resilient to prolongeddry weather as well as providing the nutritional benefits of legumes, including higher mineral levels whilst also reducing worm burdens.

Legumes

Ruminant livestock production systems face the challenge of producing more meat and milk to meet increasing world demands whilst reducing use of inputs. On the continent, forage crops are often grown in simple or complex mixtures, annual legumeswith cereals and perennial legumes with grasses. Grass– legume mixtures can produce 40% higher yields than monocultures of each species, depending on the species combination and usually provide improved nutrition than grass alone.

Using forage legumes that can fix their own nitrogen can reduce overall GHG emissions due to decreased fertiliser use (and the emissions associated with its production). Each kg of ammoniumnitrate produced by the Haber–Bosch process consumes 58 MJ of energy and emits 86 kg CO2 equivalents in the form of nitrous oxide. The IPCC suggest that for every 100 kg of N-fertiliser added to the soil, 10 kg of N is emitted as nitrous oxide (N2O) which is 300 times more potent than CO2.


Legumes offer great potential for sustainable intensification at many different stages with the soil-plant-animal- atmosphere system, most effective at 30- 50% inclusion in mixed swards. Voluntary intakes of forage legumes are 10-15% greater than that of grasses of similar digestibility. As well as the reduced use of mineral nitrogen fertiliser, other benefits of including forage legumes in swards and mixtures include lower emissions of carbon dioxide, nitrous oxide and methane both from the farm as a whole and per unit of milk or meat production, lower production costs, reducing bought-in protein feeds, increased forage production, increased nitrogen use efficiency, higher forage nutritional value, improved feed conversion efficiency and improved livestock health and performance.

The inclusionof legumes into short- term grass leys could increase the sequestration of carbon into the soil organic matter. Legumes can also enhance biodiversity and support soil organic carbon by reducing decomposition by producing decay resistant substrates.

In addition, legumes may benefit and adapt to higher atmospheric CO2 concentrations and to changing climatic conditions.

Condensed tannins

Methane production decreases with inclusion of the condensed tanninforages such as the legumes sainfoin and birdsfoot trefoil and the herb chicory in ruminant diets. Condensed tannin activityhas been found to reduce nitrogen excretion by protecting dietary protein from degradation in the rumen for more efficient digestion and absorption further down the digestive tract.The tannins also shift nitrogen excretion from urine to faeces, reducing the rate of volatilisation and leaching. Reducing methane production will also improve the efficiency of productive ruminants and decrease their carbon footprint.

Sainfoin produces high quality forage at reasonably high yields in alkaline and drought-prone soils. Inclusion of 20% sainfoin within a lucerne stand has been found to prevent bloat and improve digestibility in sheep. Increased digestibility has also been found where sainfoin is included in grass mixtures including cocksfoot.


Sainfoin can also be particularly beneficial via its anthelmintic effectwhen fed before and after lambing when immunity of the mother and newborn is low. The condensed tannins in sainfoin can also stimulate the immune response to produce more T-cells, particularly important as parasites are inherently immune-suppressive. Condensed tannins are also effective against flystrike in sheep, as they produce drier faeces, preventing flies from laying their eggs.

Further development

Breeding focus on forage crops across Europe is on increasing geneticdiversity, crossing in species to increase variation for key traits that aid adaptability in changing climatic conditions such as the resistance to fungal diseases where temperature and rainfall shifts increase their range and viability.

Increased, more precise, use of organic fertiliser and decreasing losses and leaching of applied nutrients is essential to increase nutrient use efficiency in grassland systems. Plant communities with higher speciesdiversity are expected to use resources more efficiently making mixed cropping a promising strategy for sustainable intensification. Furtherwork is neededto assess species compatibility within a wide range of mixtures.

Developing speciesand breeding varieties more tolerant to climate stresses are expected to play a crucial role in climate change adaptation and mitigation strategies. The increased role of legumes in ruminant systems will support more sustainable and competitive ruminant production systems and along with grass leys in arable rotations, their importance and value are expected to become more widely embraced in the future.

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