Soil health has risen up the agenda rapidly in recent years, making dramatic headlines in the national press.
Chris Martin, head of soil health at Agrovista, describes soil as ‘one of the most over used and overlooked resources’ on the planet.
Chris Martin suggests that unless a different approach to soil is adopted by all sectors within agriculture, the consequences could be dire.
He says: “The combination of synthetic chemistry, horsepower and fossil fuels has allowed us to bully soils.
Fertilisers and crop protection chemicals are not working as well as they used to and farmers are finding that to obtain the same yields, they are having to increase levels of inputs.
“So more fertiliser is applied to realise the same growth and extra cultivations are required to achieve the desired seedbed.
And the more we try to improve the situation by applying extra inputs or using more machinery, the worse it becomes.
“I liken the soil to an insect hotel where we create a stack of spaces for organisms to live in but then we come along with machinery and the trafficking squashes it.
We are driving a wrecking ball through it,” Mr Martin adds.
He points to the intricate inter-relationship between the physical, chemical and biological characteristics of soil, so that if one is compromised, they all ‘move out of kilter’.
Defining good soil health as the ‘ability to function effectively over a long period of time’, he says the water-retaining properties of soil are an excellent indicator of its resilience.
“I talk about the three Rs when describing the relationship between soil and water; receive, retain and release.
If a soil is to perform these three roles, it has to be in good condition.” Mr Martin refers to regenerative agriculture, where soil is the ‘number one priority’, noting that although not every farmer will fully embrace this approach, some of the principles apply to everyone.
“In the UK, we have 741 individual soil series or associations and often there will be several different soil types in the same field.
In previous generations, hedgerows would often have demarcated the boundary between the changes in characteristics and our forefathers would have had to adapt their farming methods accordingly.
“Now, we have accumulated the technology and so some farmers may no longer worry about understanding the limitations of the soil.
Previous generations would not have had these tools but now we need to learn their way of farming again because chemicals are no longer working as they used to,” Mr Martin says.
He highlights the importance of organic matter but adds it has been exhausted in many soils and the only way of putting it back is to add carbon.
The problem of degraded soils is not limited to arable systems either, according to Mr Martin, who counters the myth that ‘grass is great for soil health’ with a cautious response of ‘not always’.
He says: “If grassland is managed badly, we see the same problems.
Compaction from trafficking of heavy machinery when silage-making, or localised poaching by livestock.
“Applying large amounts of slurry to the same fields repeatedly each year will hasten selection for very narrow populations of soil biology.
Earthworm numbers will plummet under these conditions and it was Charles Darwin who referred to them as ‘nature’s ploughs’ for good reason.
“Too much slurry will poison the soil and will cause it to become anaerobic.
Very often we see a lock up of nutrients, especially phosphate, as a consequence.
We calculate P balance sheets for some farms and the results are startling, often because of the large amounts of phosphate contained in feed.” The starting point for improving soil health on any grassland farm is to ‘test, test, test’, Mr Martin says, because it provides essential insight without which a farmer is ‘guessing’ when applying manures or fertiliser.
He strongly recommends a comprehensive soil analysis which includes every essential nutrient and all the most important trace elements.
“A comprehensive soil test costs only slightly more than a basic one, working out at a few pence per acre, but the results are relevant for five years.
The basic analysis is perhaps even dangerous because it does not give the farmer enough information to make decisions.
“Whenever an Agrovista agronomist visits a farm for the first time they will carry out a provisional soil check to assess the state of the soils.
This starts with a simple visual evaluation by putting a spade in the ground to examine the soil profile.
“There is no substitute for a spade, it is one of the most under-utilised pieces of equipment on a farm.
Digging a hole allows us to examine the physical structure of the topsoil and the subsoil.
“We look at the grass sward species composition, looking for weed species to provide pointers to problems such as a low pH, nutrient imbalance or compaction.
“Combining the results of the soil analysis with the visual assessment allows us to gain a picture of the physical, chemical and biological balance in the soil.
These three factors are inextricably linked,” Mr Martin adds.
“Our agronomist will prepare a report for the farmer, highlighting short-term measures to improve the soil and longer term solutions, depending on his aspirations for soil and cropping.
“The first thing on grassland soils is usually to make sure the pH is correct.
While the target pH for grassland is normally recommended to be lower than that for arable fields, a pH of 6.5 is still optimum to ensure the main nutrients are available to the plant and so the soil biology can work properly.
“If pH is too low, we will recommend the best type of lime to use, depending on the calcium:magnesium ratio in the soil.
If pH is too high, we may need to look at phosphate liberation technology to help to make the phosphate available again within the soil.
“The detailed soil analysis will also reveal deficiencies in essential nutrients such as calcium, which is vital for all life forms and provides strength to the soil, plants and animals, and, of course, is a main constituent of milk.
“The calcium:magnesium ratio in soil is critical and will influence whether the soil is too tight when magnesium levels are too high relative to the calcium, or the reverse where the soil may be too loose.
“Other elements such as molybdenum, copper and manganese are vital for plant growth and animal health.
Farmers spend a fortune on supplements containing these but if they are in the right quantities in the soil in the first place, this should not be necessary.
“The carbon:nitrogen ratio indicates whether the soil biology is functioning properly.
Where slurry is applied regularly to soil, because it contains large numbers of microbes, the nitrogen will be metabolised very quickly.
This slows down the build up of carbon which is vital for soil health.
“In these situations we will usually advise farmers to apply box muck or another material high in carbon to bring the ratio back into line.
It is about being more targeted when applying manures, rather than simply ‘getting rid’ of them,” Mr Martin adds.
Looking to the future, Mr Martin believes technology could hold the answers for grassland farmers who are looking to improve their soils.
While advances such as controlled traffic and precision farming are now widely employed in the arable sector, they are rarely adopted on livestock farms.
Mr Martin thinks there is potential for these solutions to help address compaction and nutrient imbalances, as well as embracing the learning of our forefathers because in some respects, they may have been better farmers than us.
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