The Nitrogen Economy of the Soil - Practical Version

Your Soil May Already Be Releasing £140/ha of Nitrogen Each Year

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Most soils already contain several thousand kilograms of nitrogen per hectare, yet modern farming still relies heavily on fertiliser nitrogen produced through energy-intensive industrial processes and global supply chains. Nitrogen fertiliser markets have started moving again, driven by energy prices, geopolitics and tightening global supply. That raises an important question for farmers: How dependent should crop production be on imported nitrogen? As fertiliser prices move again, conversations about nitrogen are becoming more common across the farming community. Some of the most useful discussions are happening not in advertisements or marketing material, but between farmers comparing results, sharing observations and asking simple questions about how crops actually access nitrogen in the soil. When input prices become volatile, practical agronomy tends to move back into focus. This article examines where crop nitrogen ultimately comes from and why biological processes in the soil are becoming increasingly important.

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Version 2 – The Nitrogen Already in Your Soil (Practical)

Fertiliser markets have started to move again. Reports suggest ammonium nitrate has moved back towards £450–£500 per tonne, largely driven by rising energy prices and geopolitical tensions affecting global supply.

Nitrogen fertiliser has always been closely tied to energy markets because it is produced using the Haber–Bosch process, which converts nitrogen from the air into ammonia using natural gas.

When gas prices rise, fertiliser prices usually follow.

For farmers this creates a familiar frustration. Nitrogen fertiliser is essential for crop production, yet its price is largely controlled by factors far beyond the farm gate.

But fertiliser is only part of the nitrogen story.

Most agricultural soils already contain large amounts of nitrogen stored within soil organic matter. This nitrogen has built up over many years from crop residues, roots, manure and biological activity.

In many cases the amount of nitrogen already sitting in the soil is greater than the amount applied each year as fertiliser.

The reason crops cannot immediately use this nitrogen is because it is locked within organic material. Soil microbes gradually break down that material and release nitrogen in forms that plant roots can absorb. This process is known as mineralisation.

It happens continuously in healthy soils.

Depending on soil type, organic matter levels and weather conditions, mineralisation can release significant amounts of nitrogen during the growing season. In many arable soils this natural process supplies a meaningful share of the nitrogen a crop eventually uses.

In other words, the soil itself is already contributing nitrogen to the crop.

Fertiliser nitrogen is often used to top up this biological supply rather than replace it entirely. However, crops do not capture all the fertiliser nitrogen applied. Some is inevitably lost before the plant has a chance to use it.

This is why improving nitrogen efficiency has become such an important focus in modern crop nutrition.

Soil biology plays a key role in this process. Certain microbes can contribute small amounts of atmospheric nitrogen, but more importantly soil microbes drive the recycling of organic matter and the release of nutrients around plant roots.

The most active part of the soil is the rhizosphere, the narrow zone surrounding plant roots. Roots release sugars and other compounds that feed microbes, creating a busy microscopic ecosystem where nutrients are constantly being transformed and recycled.

Encouraging healthy biological activity in this zone helps crops access nitrogen that already exists within the soil.

This does not mean fertiliser suddenly becomes unnecessary. Modern farming will continue to rely on fertiliser nitrogen for the foreseeable future.

But it does change how we think about nitrogen.

Rather than seeing fertiliser as the only source of crop nutrition, it is often more accurate to view it as one part of a wider nitrogen system that includes soil organic matter, microbial activity and plant roots.

Most soils already contain thousands of kilograms of nitrogen per hectare locked within organic matter. The real challenge is not whether nitrogen exists within the soil, but how efficiently it is released and captured by the crop during the growing season.

Bio-N has now been used on thousands of hectares across the UK to support nitrogen efficiency in both arable and grassland systems. By strengthening the biological processes that release and recycle nitrogen in the rhizosphere, it helps crops make better use of the nitrogen already present within the soil.

Many growers are now using Bio-N as part of their nitrogen strategy to reduce fertiliser dependence without compromising crop performance.

Steve Holloway

Technical Manager