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Herbal Leys and Perennial Crops

This page explores the different herbal ley mixtures in the CHCx3 trials and their carbon capture potential. Additionally, it explores the carbon capture potential and agronomy of perennial wheat grass, Kernza

Image source: Cotswold Seeds

Background

Herbal leys are ‘temporary’ diverse forage leys (usually redrilled after ~ 4+ years to maintain diversity/vigour). They consist of a mixture of grasses, legumes and herbs/forbs and range in complexity from simple to highly complex mixtures containing different species; and varieties within species. The herbal ley trials within this project include three different mixtures with increasing complexity and a standard grass/clover ley control. The use of species and variety mixtures provides variation in terms of: palatability, nutrient content, growth habit, maturity date, rooting depth and sward architecture. Different components may perform better than others depending on weather conditions (temperature and moisture) and season (plant life cycle). This diversity supports a wider range of invertebrates, small mammals and birds. Herbal leys support more complex soil microbial biodiversity and contribute to soil structure and health. In CHCx3 we are assessing their potential to capture carbon from the CO2 from the air into the soil. In the past, herbal leys were grown more widely before the availability of inorganic nitrogen allowed predominantly grass swards to produce higher forage yields.

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Benefits of herbal leys
 

Resilience

Deeper and diverse rooting plants access water held throughout the soil profile, particularly at lower depths, thereby surviving well and continuing to grow in hot summer drought conditions. Good rooting penetration aids both water retention and infiltration/drainage, improving survival for all sward members in prolonged wet conditions. The impact is greater once the sward is well established.

Biodiversity

Flowering herbs and legumes provide pollen and nectar for invertebrates including crop pollinators. Invertebrates are a food source for small mammals and birds, invertebrate larvae being a particularly important food source for growing chicks.

Livestock

A diverse range of forage plants in the diet of cattle and sheep provides a wider range of minerals and nutrients, supporting healthy functioning, growth and production. (Care must be taken in selecting plant species for grazing breeding ewes, which may be affected by plant compounds, such as phytoestrogens in red clover, which can influence their oestrus cycle).

Soil Health

Range of rooting types and depths work further through the soil profile, physically and chemically/biologically supporting and improving soil structure and microbial activity, sequestering carbon. It can take up to four years for sufficient root development to have the maximum impact on soil structure and fertility. Herbal leys perform best if retained for a minimum of 3 years.

Agronomy

Rainfall/moisture

Species selection will need to consider soil moisture preferences, species such as cocksfoot and lucerne thrive in drier soils but struggle in wet soils whereas timothy and white clover thrive in moist soils but can quickly dry out.

Soil type & pH

Soil pH affects nutrient availability and rate of release from organic matter and soil reserves. Species such as meadow fescue and alsike clover can tolerate soils with pH down to 5.5, whereas species sainfoin and lucerne need pH of above 6.3.

Soil depth & bedrock

Deeper rooting species will make good use of nutrients and moisture lower in the soil profile but may struggle in shallower soils. Calcareous soils on chalk bedrock are ideal for cocksfoot and birdsfoot trefoil whereas a higher sand content is preferable for red clover and tall fescue

Challenges

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01

Establishment

Different species germinate and establish at different times and rates, sowing depth, moisture and temperatures levels will influence this so sowing date and conditions are important.

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Species persistence

Persistency of sown species may be variable, there may be certain soils and fields where some species will thrive and others don’t get a hold. Where stewardship options are established and funded through SFI, there may be a requirement to maintain particular species or plant types at a certain inclusion rate within the sward.

02

Weeds

Weed control though herbicide use is difficult due to the wide range of plant species present that may be sensitive to the active ingredients. Achieving a stale seedbed beforehand will be beneficial. The wide range of species, once well established should minimise weed encroachment. Spot spraying and possibly weed wiping and hand hoeing may be beneficial for any problem patches.  

04

Timing of cutting

Species will mature at different rates, the digestibility of some decreasing substantially as plants mature whilst others are slower to mature so timing of cutting for silage/haylage will need to balance biomass with feeding quality and ease of handling.

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