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Maintaining healthy soil for growing grass and forage crops

As we move firmly into autumn, and with an eye to the winter storms ahead, now is the right time to set aside some time to review soil health and planning to optimise your soils’ fertility and resilience for the seasons to come.

 
 

The soil is one of the most important assets farmers have. Growing grass and forage crops require soils to be maintained so that they have good soil structure, water retention and nutrient availability. In soils that are healthy places for plants to grow, the interactions between chemistry (pH, nutrients), physics (soil structure and water balance) and biology (earthworms, microbes, plant roots) are optimised for each particular place and environment.


Soil provides the essential link between the components that make up our environment through:

  • Exchanging gases, such as carbon dioxide, with the atmosphere

  • Regulating the flow of water and rainfall in the water cycle

  • Providing nutrients for plant growth by degrading organic matter and transforming chemical fertilisers

  • Storing, degrading and transforming organic materials and contaminants that are applied through animal and human activities or deposited by flood waters and aerial deposition.

Managing and protecting soil is therefore an essential part of protecting the environment as a whole.


Maintaining healthy grassland soils, by improving soil structure and conserving biological activity, will support better plant growth, forage quality and thus profits and will also minimise the negative impacts on the environment which can follow poor soil management. Where soil structure is frequently poor this will lead to a 10-20% reduction in grass growth, equating to around 1-2 t DM/ha. Poor structure can lead to reduced quality forage with reduced ryegrass and clover content and more weeds. A sward with 70% ryegrass will average over 11.5 MJ; over 1 MJ higher than a sward dominated by weed grasses, this reduction in quality can reduce liveweight gain significantly. With good soil condition coupled to excellent grazing management, a lamb can gain 300 g per day; however, lambs often gain only 170 g per day from pasture. Soil structural limitations may be one reason for poor yields or forage quality even where pH and nutrient availability is apparently optimum; if roots can't get to the nutrients the grass can't use them.


Draw a map


The first step is to draw a map of the soils you have. This doesn’t have to be fancy and use technical terms – identifying the stony steep bits and the places which get soggy after a week’s rain is the kind of thing I’m thinking about. You might print out a farm map, then look at it alongside satellite images from your choice of navigation software and apply your own knowledge of how the land behaves to “colour in” areas that behave similarly. You should also note any sensitive features, like historic features, watercourses or wildlife habitats. For most farms, a list of soils usually has five to ten groupings. The grouping works a bit like that for animal species and then breeds within the species; in a soil scientist’s map you’ll see reference to soil types (these have big differences between them like species) and soil series (these may be of different types, but can also be only slightly different to another series e.g. based on a small difference in stoniness or topsoil depth). But your own map doesn’t necessarily need to use these terms, it can stick with your own descriptions. This map can very quickly become the heart of your soil management plan. For each soil you have identified, keep some notes on slope, soil texture (light, medium, heavy) and what you have observed about run-off of water after heavy rain and/or soil movement through erosion. The risks of run-off and erosion are increased if the soil surface is bare – so the map should inform planning if you are thinking of how and where best to integrate arable forages and the best approaches for reseeding.


Soil assessment


Once you have a map, you can also think about linking this to a programme of soil health assessment. This brings together measurements of the soil chemistry (pH, nutrients) from soil samples with in-field assessment of soil structure and biology (earthworms, plant roots). The ideal time to do the soil health ‘check-up’ is when the soil is both warm and moist, so either from mid-autumn or as the soil warms up in the spring – whichever timing you choose it is best to stick with it so you compare like with like from year to year. Identify some spots that will give you a picture of the soil groups and management practices you have on farm – I think most farms need about 20-30 to give a good picture. Because soil properties change slowly, you don’t need to sample each site every year, so about once in five years is usually about right, unless you are making a major change to management. So, this will mean you have something like five sites on your list to look at in detail each year; and when I say in detail, you only need about half an hour to get a good look and some reference photos. But a good soil management plan will also get extra notes added regularly, based on observations during the year. You might note an area where compaction has occurred around a ring feeder or pick out an area where grass growth has been poorer (or better) than expected. In these areas, you might want to slot in an extra sample during the health check to help understand why.


A spade is the key tool for carrying out soil assessments


Digging a hole and handling the topsoil and subsoil to identify soil texture (light, medium, heavy), structure, compaction and earthworm activity, provides essential information to guide future management. We often call these tests the VESS – Visual Evaluation of Soil Structure.

Visual Evaluation of Soil Structure (VESS) showing:

Image 1: Compaction in topsoil layer due to grazing in a wet period. Good structure beneath.

Image 2: Good crumb structure to spade depth; the same block was used to count worms and we found 49 in total with a good range of species in the 20x 20 x 20 block.

(Photographs credit- Stockdale)


If you couple this with soil sampling, you can also check whether the nutrient management plan you have in place is doing the job you intend in terms of maintaining pH, preventing acidity and addressing shortfalls and surpluses in key nutrients. If any nutrients are in short supply, plant development will be compromised and overall yield disappointing. This routine soil health check can help direct you towards other more focussed soil testing to help decide whether any additional nutrients are required, allowing a targeted approach to manure and fertiliser use, saving time and money. There are a range of excellent resources that have been developed to help farmers with nutrient management. Look out for the AHDB guide - Improving Soils for Better Returns and the assessment sheet for soil structure - Healthy Grassland Soils. These are things that a farmer can do for themselves; but it’s also good to share your thoughts and ideas with others, so if you are part of a local grassland society or discussion group, you might want to make a soil walk the focus of a farm walk together.


Add soil management to your to do list


It's also important to link the map and any assessments to a ‘to do’ list. The best time for action depends on the problem; in many cases, what’s needed is patience and perhaps some fencing to let the sward and soil recover together overwinter. Active growing roots are the best way to maintain good soil structure. In some cases, metal might be needed to address severe compaction, but this needs to be done when the target layer is dry enough to fracture – structuring operations can smear the soil and do more harm than good when done in the wrong conditions. In most situations this is likely to be in the mid-late spring or, for subsoil, in late summer. But if you are mole draining then you want wet soil in the moling layer – so that is often a spring operation. Always try and follow a restructuring operation with an application of well-composted muck. Farmers, advisors and scientists got together as part of the UK Soil Health Initiative and have produced guides to help with soil management - Managing Soils for a Sustainable Future – including one targeting lowland and one for upland livestock farms.


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