Recent news headlines warn the state of our soil is now a serious threat to the environment and crops. But they also say good-quality soil can help save the planet. “No country can withstand the loss of its soil and fertility”, said Michael Gove in 2017, raising fears there are just decades of UK farming left. What are the powers and dangers of this dark material, and how worried should we be?
Soil is everywhere, in our parks, gardens, farmland, beneath our feet and under our pavements. But this extraordinary and valuable substance is often overlooked and dismissed as ‘dirt’.
We fundamentally rely on soil. It produces 95 percent of our food, be it the crops we eat, or grasses and other plants to feed animals for meat. And this is just one aspect of the goodness of the ground.
“Soil is one of the most underrated and little understood wonders on our fragile planet”, said Professor Bridget Emmett of the UK Centre for Ecology and Hydrology.
It is vitally important we take stock of this and, where we can, preserve this vital commodity. It was not until I did a Master of Science at Cranfield University in 2002 under the watchful eyes of Professor Dick Godwin and his team that included Dr Alex Vickers & DR Ian James, that I fully appreciated the science behind the soil. As a practicing turf professional / parks manager I was acutely aware of the importance of soil management when it came to maintaining managing sports surfaces and parks and open spaces.
I can vividly remember one of our first tutorials when Alex described the nature and properties of soil. It was then that I and a batch of grounds professionals that included the likes of Dr Colin Mumford, David Warner, Andy McLeod, Colin Robinson and Steve Prinn to name a few, were introduced to the vast subject of soil science.
Understanding the nature and properties of soils is a must for any turf professional. Once we know what type of soil and its composition we are dealing with, we can manage it within its geographical location. In fact, one of the best books to help you understand the complexities of soil management is the 960-page The Nature and Properties of Soils by Nyle C. Brady and Ray R. Weil.
Why is soil crucial to us?
Watch The Miracle of Soil below, a short animation to explain the power of soil and the need to care for its health.
To grow, plants need not only minerals from soil, but also carbon dioxide from air in order to make food by photosynthesis – and some of this carbon goes into the ground. Soil stores an extraordinary amount of carbon – three times the amount in the atmosphere and twice the amount in trees and forests. While soil can store or ‘sequester’ carbon, it can also lose it when degraded. The loss of the carbon in poor soils contributes to the rise of carbon dioxide in the atmosphere, one of the gases that causes climate change. In just one gram of soil, it’s estimated there could be 50 thousand species of micro-organisms, and in a single teaspoon there are more individual micro-organisms than the world’s entire human population.
Crucially, this rich ‘soil-web’ of underground life creates an open structure. This allows rainwater to seep into the ground, storing moisture for plants to make crops grow well, even in times of drought. It also prevents flooding, an important function as global warming makes extreme and uncertain rainfall more prevalent in the UK and around the world.
We must be more careful in the treatment of our soils. It usually takes around 1000 years to produce an inch depth of topsoil by natural weathering processes. We can move literally tonnes in a matter of minutes using modern earth moving machinery, we just need to be more aware of the consequences of eradicating our precious soil resource.
Knowledge and understanding of soil physical properties has always been important for professional turf managers when making decisions about maintenance operations and when carrying out reconstruction works. Precise soil knowledge, including information on boundaries between soil types, should result in more efficient use of fertilisers, pesticides and improved management practices, thus ensuring that the final managed outputs result in the production of economically safe, consistent, playable natural sports turf surfaces.
Soils can vary in many ways, both physically and chemically on a local or regional scale. Many factors, including original parent material source, climate, weathering processes, topography or history of the land use influence their properties. This soil variability gives rise to all the different soil types universally classified by soil texture composition. Soil composition (soil texture) is determined predominantly by mineral particles and organic matter content and can be classified by the percentage of sand, silt and clay mineral particle content.
The strength and permeability of any soil is determined by its structure, soil type, drainage capacity and how well it is managed. Soils will perform differently governed by the amount of water, root mass and air there is in the soil matrix.
Determining soil texture can help you learn about possible restrictions and advantages of the soil. Soil texture is related to weathering and the parent material. The three basic texture classes are sand, silt, and clay, though many soils are a combination of these textures.
In the UK we have at our disposal a number of organisations that can help us identify what soils we have. One of them is the UK Soil Observatory that provides a soil mapping service that helps identify the predominant parent material soil by geographical location. However, taking a number of localised soil samples from your pitches will easily identify your soil type. Once you have taken some soil samples and sent them off for analysis you will need to test for particle size and nutrient status.
Once you have determined your soil type based on the soil results of giving you a percentage of clay silt and sand using a soil textural triangle you can identify what type of soil you have and how best to manage and maintain it to sustain plant growth.
The Soil Texture Triangle, as shown on the image, helps us classify the soil type, these percentages are determined by undertaking a PSD, particle size distribution analysis.
The definition of soil texture is the relative proportion of sand, silt or clay in a soil. The terms sand, silt, and clay refer to relative sizes of the soil particles - sand, being the larger soil particle, feels gritty; silt, being moderate in size, has a smooth or soapy texture; clay, being the smaller size feels sticky.
Topsoils are complex arrangements of mineral particles, air, water, organic matter, living organisms and nutrients. The proportion of these elements is not always critical, however it is important that a soil contains all these elements in one form or another.
Topsoil is a major component of almost all natural sports turf facilities, the exception being pure sand constructed facilities. Its primary role is to provide a medium for grass growth that is both sustainable and stable. This sustainability and strength only comes about when the soil has a good structure.
Soil, naturally, is separated into layers called horizons. These horizons are described as topsoils and subsoils. Topsoil material is generally darker due to the impact of the organic matter that has incorporated itself within this layer. This organic matter is also responsible for enhancing the physical properties of the soil such as tilth, structure, water infiltration and water holding capacities.
The topsoil horizon plays a major part in plant growth and biological diversity as well as some hydrological processes. Topsoil is the interface of air, minerals, water and life (soil organisms), which all interact with one another to support and maintain a soil structure.
The four major components of soil are air, water, mineral matter and organic matter. The relative proportions of these components greatly influence the behaviour and productivity/performance of the soils.
The ideal volume composition of a loam topsoil, for example, would be a pore space of 50% air and water, with 45% mineral matter and 5% organic matter. The proportions of air and water will fluctuate as the soil becomes wetter or drier.
However, we need to find better ways of safeguarding our precious soil resources. We must not lose sight of its true immense value to the planet and begin finding better ways of protecting and manage this valuable resource for future generations.
Information displayed on the WWF website states, half of the topsoil on the planet has been lost in the last 150 years. In addition to erosion, soil quality is affected by other aspects of agriculture. These impacts include compaction, loss of soil structure, nutrient degradation, and soil salinity. These are very real and at times severe issues.
The effects of soil erosion go beyond the loss of fertile land. It has led to increased pollution and sedimentation in streams and rivers, clogging these waterways and causing declines in fish and other species. And degraded lands are also often less able to hold onto water, which can worsen flooding. Sustainable land use can help to reduce the impacts of agriculture and livestock, preventing soil degradation and erosion and the loss of valuable land to desertification.
We can undertake several steps to help preserve soil erosion these include maintaining permanent vegetation, reduce farming and gardening activities, plant cover crops. As the name suggests, cover crops provide a protective cover for soils in between the main plantings. Their function is the same as the function of permanent vegetation. They protect soils from rain and wind, slow down runoff and encourage water infiltration.
Mulching bare soils, increasing organic matter, controlling water runoff, sustainable grazing and Afforestation, the planting of trees. All these activities over time will certainly reduce the loss and erosion of our precious soil.