Managing Grassland Under Organic Systems
25 October 2024
The principles of organic farming place food quality, human health, environment, animal welfare and socio-economic aims at the core of their production systems. Organic farming regulations promote practices which do not involve the use of synthetic or manufactured products in crop production.
Due to the restrictions around the use of inorganic compounds such as fertiliser and agrochemicals, management of crops under an organic system requires a greater emphasis on working in harmony with natural processes. This involves ensuring biological processes such as nitrogen fixation and nutrient cycling are optimised and adopting management practices such as exploiting the genetic advantages of different plant species.
An effective organic grassland system is dependant on 5 key areas:
Soil management
The fundamentals of crop production, whether on a conventional system or an organic system, all depend on a soil environment which is not limited by compaction, ineffective drainage, poor fertility or poor biological activity. Soils which have layers of compaction will affect the ability of growing plants to develop strong roots and access water and nutrients, impacting yield and plant health. A shortage of soil organic matter and any restrictions in how water flows through soils will result in soils which are less resilient.
If water cannot flow through the soil profile, they become waterlogged, creating an anaerobic soil which limits the roots of plants and their ability to absorb nutrients. Soils with low soil organic matter levels struggle to retain nutrients and water during prolonged periods of dry weather. Plants are then at an increased risk of stress from a lack of water and nutrients and risks disease developing or crop failures.
Figure 1. Visual Assessment of soil structure (VESS) guide
To find out more about assessing soil health see Healthy-grassland-soils.pdf (fas.scot)
Top Tips
- Rotate fields which are cut for silage to prevent compaction from repeated machinery use.
- Use the soil type of fields to help determine how they are managed and what crops are best suited to those sites.
- Ensure drains and ditches are maintained to provide adequate field drainage.
Crop choice and rotation
Under an organic farming system pesticides cannot be used to control weeds, and inorganic nitrogen cannot be used to manipulate growth. Crop choice, seedbed preparation and timing of sowing are imperative to ensure the new crop establishes faster than any weeds which may compromise plant population. Where a new crop is being sown it is critical that those plants have the soil conditions and fertility which enable them to establish quickly and out-compete any emerging weeds.
Cereal crops either as a standalone crop or with grass under sown are useful as they establish quickly and compete with weeds. A cereal crop also offers an opportunity to remove weeds with the crop when it is harvested leaving a seedbed which can be drilled into directly and minimising any further soil disturbance in which weeds would germinate. An under sown cereal crop will benefit from being sown with a leguminous plant partner such as spring barley and peas to provide nitrogen to the cereal crop and subsequent crop.
Grass and red or white clover are the most widely used crops in organic livestock systems. Both red and white clover are perennial plants, with red clover persisting for 3- 5 years and white clover significantly longer if managed well. When combined with a perennial ryegrass sward under the correct management there is opportunity to grow a high yielding crop, with high metabolizable energy and protein content and a high degree of flexibility in how it is harvested, either in silage or through grazing. These swards are also suited to different livestock categories and offer year-round use. Clover and perennial ryegrass swards require optimum soil conditions and base fertility to ensure that they have the availability of nutrients to thrive. Careful management of grass canopies and the intensity of cutting and grazing is also required.
You can find out more about managing red and white clover here: Maximising Clover in Grass Swards | Helping farmers in Scotland | Farm Advisory Service (fas.scot)
Herbal leys or multi species swards have increased in popularity due to the high-quality forage that the combination of grass, herb and legume offers to livestock. Establishment of herbs and legumes is challenging as often the competition from weeds can be too great with germinating plants smothered. The successful establishment of a grass, herb and legume sward will be determined by control of weeds in the years prior to its establishment so it is important to plan a rotation which is aimed at providing the best opportunity for a new ley to establish.
To find out more about using a herbal ley visit: Why Grow Multi-Species Swards? | Helping farmers in Scotland | Farm Advisory Service (fas.scot)
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Top Tips
- Cereal crops offer a valuable nurse crop when establishing new leys of grass. A cereal companion can help to compete against weeds and if harvested as a wholecrop provides an opportunity to cut and remove any annual weeds which have germinated. Sow the cereal component at half rate to ensure the grass which is under sown gets sufficient sunlight.
- Inclusion of another legume in a wholecrop mix such as peas or lupins can also help to fix atmospheric nitrogen and leave some N for the newly established grass post-harvest. Choose a cereal and legume mixture with similar maturity dates and harvest early to allow under sown grass time to recover.
- Assess the weed burden of each field on a case-by-case basis to identify those fields which may require heavy cultivation to plough down any weed seeds and those with a lower weed burden which are better left undisturbed or may be rejuvenated with a minimum till or direct drill method. Avoiding overgrazing and poaching in wet conditions and maintaining soil fertility will help keep the grass sward competitive and prevent space for weeds to establish.
- Grass and clover swards are the cornerstones of organic forage production, monitor soil fertility closely and follow key grazing principles to maximise this crop. A clover content of 30% should be targeted to provide optimum N through fixation.
- Herbal leys with legumes offer a high-quality forage which can fix its own nitrogen. Ensure weeds are controlled before sowing a herbal ley as these swards can be slow to establish and quickly become overpowered by weeds.
Crop and soil nutrient management
As with all crops the requirement for major nutrients such as potash and phosphate depend on the soil requirements and the crop yield. Recommendations do not differ between those made for grassland in a conventional system as they are related to the yield of crop, which is removed, but the sources of that nutrient required are more limited.
Under an organic system any soils with a low status for P and K will impact crop yield far more than in a system where nitrogen can be used to enhance growth. It is critical that there is an accurate account made for the removal of P and K in crop yields and its replacement with organic manures or rock-based products. Similarly, where soil pH is below the recommended level the impact of this on soil health and crop yield and health will be elevated.
Recommendations for phosphate, potassium and sulphur applications to grassland can be found in Technical Note 726 – Fertiliser recommendations for grassland: fas.scot/downloads/tn726-fertiliser-recommendations-for-grassland-scotland/
Advice on liming Scottish soils can be found in Technical Note 656 – Soils information, texture and liming recommendations: fas.scot/downloads/technical-note-tn656-soils-information-texture-liming/
Top Tips
- Soil sampling should be carried out every 4 years, or more frequently for higher value crops or where offtakes have been higher than anticipated. Soil samples are the most accurate measure of the available nutrient levels in the soil.
- Analysis of organic manures and preparation of a nutrient management plan will help to ensure organic manures are targeted to the areas which require it most.
Weed control
Weeds compete with plants for water, sunlight and nutrients limiting the yield of the sown crop. Whilst it is unrealistic to strive to have no weeds on farms, a regular programme of control should be adopted to limit their impact on crop and livestock output.
A competitive crop is the main tool which can be used to limit weed ingress in organically managed grass swards and crops. Optimum soil health and fertility are critical in ensuring the desired crop establishes quickly and grows vigorously.
It is important to understand the life cycle of weed plants to ensure any control which is through topping or grazing is done at the appropriate time and prevents that weed from reproducing and spreading more seeds.
Thistles and docks are arguably the most common weeds affecting grassland systems. Docks are particularly prolific with each plant shedding up to 60,000 seeds which can be viable in the soil for up to 80 years. 16% of weed seeds are viable 6 days after flowering with 90% of green seeds viable 18 days after flowering. Dock roots have regenerative buds on the root crown down to a depth of 10-12cm and can resprout due to their deep roots and nutrient reserves. This demonstrates the importance of digging out or cutting docks before flowering to prevent further spread. The dormancy of seeds should also be a factor considered when deciding if a full reseed and full cultivation are the best option.
Creeping thistles affect the utilisation of grass as livestock are often reluctant to graze around them, but they can also create an entry for harmful soil borne bacteria such as orf to get into livestock, affecting livestock growth.
More information about the physiology of key grassland weeds can be found at: fas.scot/downloads/tn643-weed-management-grassland/
Top Tips
- Prevention is better than cure – dig out or top weeds to prevent flowering and spread of seeds.
- Carry out an annual sward assessment to monitor the weed infestations and ingress of weed grasses to help determine timing for any reseeding.
- Avoid poaching and overgrazing to prevent areas of bare soils which can become dominated by weeds.
Sward management
Modern ryegrasses which form the basis of productive swards respond well to rotational grazing. Ryegrass plants which are grazed when the plant has 3 leaves, which is typically 8cm and then grazed down to 4-5cm, can recover faster as there is still some leaf to intercept light and root reserves are not diminished. The ability to recover faster gives these swards the ability to compete with weeds, but it also encourages tillering and longevity of the sward. Rest periods between grazing should reflect grass growth and will vary throughout the year, from 21 days during peak growth to 100 days in winter.
Canopy management in grass swards ensures the emerging daughter tillers and clover leaves get enough sunlight to thrive. Managing the height of grass swards and consequently the sunlight which reaches the base of the sward in Spring and Autumn is essential to promote new growth and development in clover and grasses. Regular grazing also prevents a build up of dead material at the base of the sward which affects the quality and utilisation of grass. A build up of dead material can also result in areas of bare soil emerging which gives weeds an opportunity to develop.
If working with herbal leys, these swards will require a longer rest period and should only be grazed down to 7cm to prevent damage to the growing points on herbs such as chicory and red clovers. Avoid overgrazing or poaching grassland with affects productivity and competitiveness of the sward.
Figure 2. AHDB Understanding grass growth for beef rotational grazing
For more information on rotational grazing visit fas.scot/downloads/rotational-grazing/
Top Tips
- Ensure grasses are grazed well in the spring to let sunlight into the base of the sward to emerging grass tillers and clover plants.
- Monitor the species of grasses within swards to help determine when it may be appropriate to reseed.
- Use topping as a method to manage grass growth during peaks and prevent weeds shedding seeds.
Lorna Galloway, SAC Consulting
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