Soil health has risen to the top of the agenda for the agricultural industry over recent years.

At the recent Farmers Weekly Soils in Practice event on a Lincolnshire farm, experts gathered to offer information and advice on better soil management. Adam Clarke picks out some take-home messages.

1. Defining a healthy soil

With more than a thousand physical, chemical and biological properties to measure within a soil, Cranfield University soils expert Jane Rickson explains that it is extremely difficult to define a “healthy” soil in simple terms, but growers are advised to focus on improving the “Pivotal 5” of structure, organic matter, biota, nutrients and water-air balance. This will help achieve higher and more consistent crop yields and quality.

Unhealthy soils are much easier to define. They are usually suffering from degradation by, among other things, erosion, compaction and organic matter decline. Halting any degradation and improving the Pivotal 5 is said to be a key component of “sustainable intensification” in the future.

See also: How science and technology could save our soils

2. The importance of organic matter

Although on average organic matter makes up just 5% of a soil’s constituents, it is the “engine” that drives all the major functions, according to Adas principal soil scientist John Williams.

These functions include aggregation and structure, water storage and movement and carbon storage. In addition, it provides a food source and habitat for soil biology, which dictate nutrient cycling and the fertility of a soil.

There are several options for improving organic matter, including reverting to permanent grass, introducing rotational grass, using cover crops or adding organic manures to land.

Introducing grass might not be suitable or practicable for some, while cover crops haven’t been shown to offer significant short-term increases in organic matter.

Defra-funded research shows adding organic manures is the most effective way of raising organic matter and nutrients in soils in the short term, but there are some significant differences in types of manure and their effect on soil functionality.

Farmyard manure breaks down rapidly in the soil, so more needs to be applied over a longer period to build organic matter, but it better supports all the physical and biological activity in a soil by feeding all the beneficial bugs.

Green compost is slightly different, with its lignin-based make up seeing higher retention and greater increases on bulk soil organic matter. It does boost physical and biological activity, but to a lesser degree than farmyard manure.

In addition to improvements in structure and biology, Yara’s Mark Tucker said building soil organic matter also has significant nutritional benefits too.

Higher levels help hold on to levels of potassium, calcium and magnesium in the soils, provide a source of nitrogen and maintain availability of micronutrients for crops. In addition, mineralisation of phosphate and sulphur from organic matter can help farmers reduce artificial fertiliser inputs.

3. Measure to manage

Knowing the status of a soil’s health and targets for improvement are essential to better management and in a practical field-based session, Cranfield University’s Lynda Deeks encouraged farmers to implement routine soils inspections and gather data to benchmark impacts of farm operations.

Several observations can be made both in the field and by sending off samples to the lab, all centred around a field history log (see table) and the “pivotal 5” of structure, organic matter, biota, nutrients and water-air balance.

In addition to building data from a routine field history log, several other measurements can be taken to help keep track of soil health:

Soil organic matter – Samples can be sent away to the lab for analysis. In the field colour can be a good indicator of organic matter level, so photos taken of a soil profile with a white balance reference can provide a good benchmarking tool for any changes. In Scotland, there is a smart device app available for this purpose.

Biota – mustard extraction or hand sorting can help count earthworm numbers, with guidance available on AHDB’s GREATsoils website, CO2 burst kits can help indicate soil microbal activity and measuring depth and spread of root systems can indicate if plants are getting the most out of the soil in terms of water and nutrients.

Nutrients – laboratory analysis will give by far the most accurate measurement of soil nutrients, although test strips for nitrate, ammonium and pH are available for field-based assessments.

Structure – Soil structure assessments can be made using either the Visual Evaluation Soil Structure (Vess) method or Visual Soil Assessment (VSA). Information of these can be found on the Scotland’s Rural College (SRUC) website or Leaf website, respectively.

Rills (small streams) or gullies are indicators of structural problems and should be recorded. A penetrometer is also a useful tool for assessing/locating soil compaction problems.

Water/air – Drains should be checked for flow during the winter and infiltration can be measured using a single ring, which is filled with water and time taken for it to soak away observed.

SoilQuest’s Stuart Alexander also highlighted the usefulness of precision-farming techniques, such as electro conductivity (EC) scanning for soil texture, that enable growers to target soil assessments and management in different zones.

4. Cover crops

From Agrii’s research work at its Stow Longa trials site and on host farmer Andrew Ward’s land near Leadenham, Lincolnshire, the agronomy company’s research and development manager Steve Corbett has demonstrated the benefits of cover crops for improving soil structure, particularly on heavy soils.

However, he warned that they aren’t a silver bullet for correcting soil structure issues and roots should be combined with steel to get maximum benefit from cover cropping.

A step-by-step plan is essential, with early cultivation, appropriate species, good establishment and destruction all factors that need to be considered to ensure the following crop is sown into a friable “drilling zone” and grassweed issues haven’t been exacerbated.

5. Cutting compaction

Soil compaction is a major problem in UK agriculture as it reduces crop yields and water infiltration, plus increases the draught forces required to cultivate land, ramping up a farm’s diesel bill.

Compaction has an estimated economic cost of about £0.4bn/year across England and Wales.

Reducing axle loads and switching to low ground pressure tyres are the best ways of minimising compaction, according to Harper Adams University’s Dick Godwin, while opting for tracks on heavy kit such as harvesters also helps. Changing from a plough-based system, where 85% of the ground is trafficked, to min-till (65%) or direct drilling (45%) will also reduce soil being damaged by wheels.

Controlled traffic farming (CTF) – where implements are kept to strict lanes using GPS guidance – is another effective way of reducing compaction, with Niab Tag research suggesting a 10-15% yield increase after adopting the system.

6. Avoid recreational tillage

Choosing the appropriate cultivation method at the right time and with good agronomic reason is key to avoiding unnecessary soil structure damage and can save time and money, too. Simon Brown of kit maker Amazone said there are five golden rules for avoiding “recreational tillage”:

• Only go as deep as necessary – this will depend on factors such as grassweed pressure, with shallow cultivations ideal where trying to avoid bringing viable seed to the surface.
• Be as flexible as possible – choose a cultivator that has plenty of depth adjustment, options on implement combinations and different tine and disc options to match to condition or intended outcome.
• Manage soil moisture – the choice is to preserve it or lose it. In the autumn, minimal disturbance is advised to avoid losing too much, while in the spring soil may require moving to dry it out.
• Incorporating residues – incorporating straw helps to trigger the residue breakdown process. As a rule of thumb, you need 1.5cm of tillage depth for each tonne per hectare of straw. Where baling and removing, lighter cultivation will suffice.
• Timeliness – taking advantage of any moisture by cultivating immediately after combining is advised to create a stale seed-bed. Don’t work too fine too early, or it could cause structural problems if the weather turns wet.