Crop rotation, seaweed extracts, lime, and a range of organic materials can all improve soil health and crop yields. Professor Geoff Dixon shows you several ways to improve your soil.

Rapidly rising costs of living are affecting all aspects of life. Increasing costs of fertilisers are affecting food production, both commercially and in gardens and allotments.

Wholesale prices of fertilisers have jumped four-fold from £250 to £1,000 per tonne within six months. All forms of garden fertilisers are now much more expensive. Crops, especially vegetables, only thrive if provided with adequate nutrition (see nitrogen-deficient lettuce below). Consequently, fertiliser use must become more efficient.

Nitrogen deficiency in lettuce.

Healthy, fertile soils achieved through good management are key to this process. That ensures roots can take up the nutrients needed in quantities that result in balanced, healthy growth.

Soil pH is a major regulator of nutrient availability for roots. Between pH 6.5 to 7.5, the macro nutrients, nitrogen, phosphorus, and potassium are fully available for root uptake. Below and above these values, nutrient absorption becomes less efficient.

>> How much soil cultivation do you need for your vegetables? Find out more in Prof Dixon's blog on cultivation.

As a result, soluble nutrients are wasted and washed by rainfall below the root zones. Acidic soils can be improved by liming in the autumn. Sources of lime derived from crushed limestone require up to six months to cause changes in soil pH values. Lime should be used in ornamental gardens with caution as it can result in micronutrient deficiencies.

Iron deficiency in wisteria.

Soil health and fertility are greatly increased by adding organic materials such as farmyard manure and well-made composts. Increasing soil carbon content helps mitigate climate change while raising fertiliser use efficiencies.

Beneficial soil biological life such as earthworms, insects, benign bacteria and fungi are greatly encouraged when you increase soil humus content. Using crop rotations, which include legumes, raises natural levels of soil nitrogen. This is a result of legumes’ symbiotic relationships with nitrogen-fixing bacteria.

Leafy vegetables such as brassicas require large amounts of nitrogen and, hence, should follow legumes in a rotation. Avoiding soil compaction encourages adequate aeration, benefiting root respiration and providing oxygen for other organisms.

Organic materials are of great value in ornamental gardens when applied as top dressings in late autumn or early spring. This provides two benefits: a slow release of nutrients into the root zones as decomposition occurs, and prevention of weed growth.

Inorganic fertiliser use can be further minimised by using proprietary seaweed extracts. These contain macro- and micro-nutrients plus several natural biostimulant compounds that aid healthy ornamental plant growth and flowering (illustration no 3 rose Frűhlingsgold).

Rose frűhlingsgold

Written by Professor Geoff Dixon, author of Garden practices and their science.

Think of Earth as an apple and the soil as the peel. Now, imagine that more than 70% of this apple’s surface is covered in water. That veneer of peel suddenly seems very small indeed.

Dig beneath the surface and you realise that the world’s soil resources aren’t as plentiful as you first thought. When you take into account all of the uninhabitable, non-arable land on our planet, including the snow-bound poles and deserts, you’re left with just 3% of total landmass to grow all the fruit and vegetables we eat.

After reminding her listeners of some stark facts at the Soil resources in the UK: overlooked and undervalued? webinar, Jane Rickson, Professor of Soil Erosion and Conservation at Cranfield University, reminded us that soil is a precious, finite resource. “We’re dealing with a very thin resource that has to deliver all of these goods and services.”

You just need to think of your breakfast, lunch, and dinner to realise just how important soil is. Of all the food we eat, 97% comes from terrestrial sources. However, in recent decades, the many benefits brought by soil have been taken lightly. Apart from providing food, animal fodder, and a surface for football, it plays a vital role in climate change mitigation.

‘Soil is excellent for climate change mitigation,’ said Professor Rickson, recipient of the prestigious Dr Sydney Andrew Medal for 2021. ‘We know that healthy soils can support vegetation and crops and plants in taking out atmospheric CO2.’

A cross section of soil layers. Unless you live on fish and seaweed, it’s likely that almost all of your food sources will come from terrestrial sources.

However, she and her colleagues at Cranfield University have unearthed some unsettling facts about the state of our soils. She mentioned that 12 million hectares of agricultural land worldwide is lost each year due to soil degradation. In the UK, soil erosion rates can be as high as 15 tonnes per hectare per year, with soil formation rates only compiling at a rate of 1 tonne per hectare per year; and, based on current rates of erosion, some soils could disappear completely by 2050.

So, what is being done to arrest this problem? The obvious mammoth in the room is climate change, with extreme weather events such as flash floods precipitating a huge amount of soil erosion. Obviously, climate change mitigation measures on a national scale would help, but adjustments to farming practices could also improve soil resilience on a more local level.

A lot of work is also being done to reduce the intensity of farming to improve soil health. The aim, according to Rickson, is to maintain a fertile seedbed while retaining maximum resistance to soil degradation. There are lots of different ways to do this.

One approach being taken is cover cropping, whereby a crop is grown for the protection and enrichment of the soil rather than for immediate sale. This enriches the soil and helps prevent soil erosion. Another approach is strip-tillage – a minimum tillage system that disturbs only the portion of the soil that contains the seed row, with the soil between rows left untilled. She also mentioned the benefits of soil improvement, with poultry manure and mushroom compost used to improve soil health by Benedict Unagwu among others.

Cover crops such as vetch and oats improve the structure and fertility of the soil.

It is difficult not to have sympathy for farmers at the moment. Climate change falls heavily upon their lands, and they must battle flooding and drought to keep their farms financially viable. Professor Rickson often speaks to the farming community about soil health, with the focus placed on realistic solutions. As one farmer told her: ‘It's hard to be green when you’re in the red.’

Perhaps soil doesn’t capture the imagination the same way as an oak forest or a field ablaze with wildflowers, but its mismanagement is costing us a fortune. She estimated that the combined annual economic cost of soil degradation in England, Scotland, and Wales is £1.5 billion.

According to Professor Rickson, the US is probably the home of soil conservation following the harsh ecological lessons learnt from the Dust Bowl disaster of the 1930s. However, she believes the UK has plenty of knowhow in the area.

‘The UK has an opportunity to be world-leading in this,’ she said. ‘I think we are as good as anyone. Our scientific community understands soil and is really pushing the boundaries in terms of soil science.’