Multi-Species Swards

3 May 2023

Multi-species swards are another name given to herb and legume rich leys. It is a grass ley typically containing a minimum of six or more species that grow simultaneously. Increasing the diversity of grassland has benefits to both livestock and the wider environment alike.

Why grow a multi species sward?

For many years the establishment of perennial ryegrass and clover leys has been considered the automatic choice for almost all ruminant livestock producers. However, over recent years awareness of the benefits of herb and legume rich leys have made them become more popular.

There is early but increasing evidence that despite the forage yield per hectare from multi species swards sometimes being lower, livestock can grow faster, achieve a higher feed conversion rate and thus have higher Daily Liveweight Gain (DLG). The diversity of species within a herb-rich sward can often provide trace elements that can be limited in a ryegrass system. Choice of species can influence the nutritional value of a sward, with legume species such as clovers able to provide high protein values both in the field and as a forage product. Therefore a more nuanced focus on margin per hectare rather than outright yields of forage dry matter demonstrates the attractiveness of this system.

The yield of a conventionally farmed perennial rye grass ley is likely to outstrip a herb and legume rich ley in a tonne per hectare measurement. However, there may be other benefits such as increased sward resilience during sub-optimal growing conditions and a longer growing season due to the diversity of species. The average Metabolisable Energy (ME) density of a herb and legume rich ley (11.5 MJ ME) can be very similar to that of a perennial ryegrass ley (12 MJ ME). Furthermore, the variable costs of growing herb rich leys can be much lower as there is often a reduced input requirement; many ‘traditional’ grassland species are deeper rooting and therefore less ‘hungry’ for applied nitrogen.

Perennial Ryegrass Ley

Positives:

Rapid to establish and fast growing
Readily responds to N applications
High energy conversion
High yielding in first 2 years

Negatives:

Demands Nitrogen supplementation
Poor uptake of trace elements
Shallow rooting
Less stress tolerant

Multi-species swards

Positives:

Improved soil structure & soil carbon
Increased palatability
Greater rooting mass
Greater trace element & mineral access
Increased stress tolerance & resilience to drought
Longevity of sward
Faster growth rates from livestock
Anthelmintic properties
Improved biodiversity

Negatives

Potentially reduced yield potential
Slower to establish
Less responsive to N application
Chemical weed control difficulties

Practical considerations with the establishment of herbal leys

Many principles of establishing a multispecies sward are very similar to those of establishing a conventional grass ley. Consideration of the previous cropping and the seed mix that is being drilled will help guide what mechanical intervention is required.

Minimising soil disturbance and the disruption of established biological networks already functioning in the soil must also be considered. Ensuring that the status of the soil is known before undertaking cultivation can mediate disrupting an already functional system. Therefore, digging a small soil pit and inspecting the soil profile for compaction or other limiting features will demonstrate whether mechanical intervention is required. Soil disturbance can often be unnecessary beyond that of ensuring good seed to soil contact.

Cultivation is not only costly for time and fuel expenses, but also results in carbon release back into the atmosphere; as such, it is important to consider the wider environmental and economic costs before undertaking cultivation. There are many farmers who are using alternative methods of improving plant diversity which include overseeding, slot seeding and direct drilling.

Making good soil contact with the seed is essential to a successful germination and achieving a good establishment. Small seeds need to be on or very near the surface so therefore broadcasting may be recommended. After drilling, consolidation is important to maximise this seed to soil contact, so rolling is highly recommended. Do not confuse soil consolidation with compaction. Compaction will occur if field work is undertaken when soil moisture levels are elevated or at a level when the soil is plasticised.

The following questions are worth assessing in advance of the establishment process:

1) What is the condition of the soil, is there soil compaction, and at what depth in the soil horizon?

If Yes – this should be addressed, therefore a machine that goes beneath this depth of the compacted layer may be required. You could consider sub soiling, chisel ploughing, or mouldboard ploughing etc. Or would soil management such as a deep rooting cover crop help to mediate the problem

2) What soil type do you have, is it easily friable, what are soil moisture levels like? Is there a particular time of year when it is more workable?

3) What are the Soil Organic Carbon levels? Are they already high and is the soil structure good – select establishment method to aid or maintain this soil condition.

4) What is the current and historic cropping for the field, are you working a stubble or an established grass ley?

5) Can you control weeds with a stale seed bed or integrating livestock grazing? Or do you have a significant injurious weed infestation that may require chemical assistance?

6) Are you looking to grow with a nurse or companion crop?

7) What machinery and cultivation kit do you have access to, would using a specialist contractor be more economic?

Timing of establishment

Herbs and legumes require higher soil temperatures than grass to germinate, 8 – 10°C is recommended. Early and late season establishment with more marginal temperatures will lead to greater grass dominance within the ley. Therefore, establishments from mid-April through to the end of August will benefit the herbal and legume species establishment. Soil moisture and rainfall events after establishment are also important to the success of the ley.

Grazing management of your herbal ley

Grazing herbal leys using set stocking systems can rapidly degrade the diversity in the sward as livestock will selectively graze their preferred species, preventing the plants from successfully establishing

Rotational grazing is therefore highly recommended to sustain the diversity of a mixed species sward. The recommendation is that a group of animals should not be in the same area for more than 3 days. Ideally grazing or cutting should occur when most species have finished flowering to aid seed return, resulting in grazing at much longer sward heights. The animals should be removed or back fenced off the grazed area to allow the sward to regrow and recover. This helps sustain the sward diversity and sustains soil structure and soil health as there is lower risk of compaction. Rotational grazing with a 28+ daybreak also increases the overall yield of the sward across the year.

The inclusion of cutting for conserved forage can have the same effect. However, over time it will lead to certain herbs being favoured over others, but this just increases the diversity across the farm as whole.

Useful resources:
Agricology Herbal Lay Webinar Series
British Grassland Society Webinars
SWARM Knowledge Hub- Diverse Forage

SWARM Knowledge Hub- Multispecies Swards