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Crops and Soils Bulletin June 2023 – The Benefits of Grass Leys in Arable Rotations

20 June 2023

This article is produced as a part of the FAS Crops & Soils Bulletin. Subscribe now to receive the full report in your inbox monthly.

The humble grass ley, often overlooked, often mismanaged and often left out of rotations. Some people may say it is not so humble when you look at some of the establishment costs! However, the benefits grasses and legumes bring in a rotation can far outweigh the establishment costs and season(s) loss of some cropping as they are key to sustaining: future yield of many cash crops, the resilience of the plants in the rotation and the soils health. This brief article aims to look at what benefit this management action can have and what one should look out for to effectively establish this temporary ley and take advantage of it.

Establishing temporary grass in the cropping rotation involves converting arable land to grass for at least 1 growing season but can be up to 5 years depending on the soil type and the farmer’s objectives (Grass leys can be kept longer than 5 years but is classed as ‘permanent’ after this age). It is necessary to select the correct grass/legume species for the single/many purposes of the role it will play in the rotation. For example, will it be grazed to provide a protein source for the stock and at the same time rest the field and build up SOM (soil organic matter). Or will it be grown to bring up the natural mineral nitrogen in the soil so you can reduce your artificial nitrogen input for the next crop. Or will the main reason be to be used as part of an integrated crop management (ICM) plan to supress nuisance weeds that are plaguing the cash crops.

Some examples of the benefits of a grass ley:

a) Breaks Pathogen Life Cycles - Growing temporary grass reduces pathogen populations by breaking their life cycle through displacement from host plants.
b) Increases Beneficial Microorganisms - Temporary grass enhances beneficial microbial populations that compete with pathogens hence reducing their virulence.
c) Improves Soil Quality - Growing temporary grass improves soil organic matter content which increases nutrient availability, water retention capacity, and porosity.
d) Reduces Pesticide Use - Using temporary grass reduces pesticide use since the field has been ‘reset’ with the grasses suppressing many types of pests naturally, hence reduces environmental pollution.
e) Enhances Biodiversity - Growing temporary grass promotes biodiversity by providing
f) Provides Feed and Fertiliser - Allows livestock to either graze or have the foraged conserved for them, which also provides the opportunity to have the field either naturally or mechanically dunged which improves nutrient availability for the next crop whilst feeding the soil biology.

The grass/legume species selected, and method of establishment will determine how long you want the ley to last and at what cost. For example, if one was short of silage ground for a couple of seasons and needed to establish a short-term silage ley, by selecting the varieties and species that are bred specifically for this purpose will provide you with the greatest chance of achieving the tonnes of dry matter from the crop, but also will result in that ley only growing for the few season(s) it was bred for without competing with the next crop in the rotation. It goes without saying that the species selected should be appropriate to the climatic conditions of the field. There is no point selecting species however great they are in their rooting system, high nutrition or nitrogen fixing abilities etc., if they are not suited for your soils and your location.

Boots in Grass

Establishment of a grass ley can be done in many ways, whether under sown as a catch crop (which has greening EFA benefits), mintilled and put in with a one pass in the spring or ploughed and conventionally sown in the autumn it all comes down to the sowing type recommendations of the seed, operators sowing ability and knowledge of the local conditions and the farmers policy of tillage. New grass leys are a hungry crop and needs access to nutrients to thrive, check out the technical notes below on how you can make sure the crop can have its ideal nutrition levels met.

Grass also needs sufficient moisture to establish and while generally we are not short of it in Scotland, we have experienced droughts recently and this stress will affect their growth progress and in turn reduce their effectiveness in maintaining soil structure, fertility and whatever use they were selected for. Also, it is important to also think about the desiccation plan of the grassland prior to the next crop being established, as depending on the farm’s policy the options to do so may be limited.


In summary, arable farmers should have grass leys in their rotation. However, one must be clear about the purpose of the ley, be informed on the species selected, have a cost-effective method of establishment and have a plan for utilisation and removal before preparations are made for the next crop. Do not miss out on the benefits from a grass ley!

Speak to your local advisor or agronomist before making decisions around rotation changes as in some cases bringing in a grass ley might be less advantageous depending on the type of following crops and the historic pest issues.

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