The Nitrogen Surplus and the Nutrient Balance Flow Chart

Surplus nitrogen

The nitrogen surplus refers to nitrogen-based compounds that are not used up in agriculture. This is calculated by subtracting the volume of nitrogen compounds used as inputs (including in the form of feed concentrates and fertilisers) from the amount of nitrogen that is fixed in animal products (meat, milk, eggs) and plant products (arable crops and horticultural crops). The volume of nitrogen-based compounds removed from the agricultural sector – for example, through exports and manure processing – is also taken into account. The surplus nitrogen may either remain in the soil or disappear into the atmosphere. A large nitrogen surplus has an impact on nature and the environment, including eutrophication (water pollution caused by excess nutrients) and the acidification of soil and surface water.

The nitrogen surplus is divided into nitrogen that is released into the atmosphere and nitrogen that ends up in the soil. The agriculture-related nitrogen surplus in the Netherlands stood at 295 million kilograms in 2024: 75 million kilograms of nitrogen entered the atmosphere and 220 million kilograms ended up in the soil.

Nutrient Balance Flow Chart

Movements of nitrogen in agriculture (inputs, outputs and feedback loops) are visualised in the Nutrient Balance Flow Chart. The full version contains 102 different quantifiable items, but this article uses a simplified version of it, which will be explained item by item. The most important sources of nitrogen-based compounds are feed concentrates (used in livestock farming) and artificial fertilisers. Nitrogen-based compounds exit the agricultural sector in the form of animal products (meat, milk and eggs), plant products (crops, vegetables, fruit and ornamental plants), or through the sale of manure outside the agricultural sector, such as for export.

The Nutrient Balance Flow Chart for 2024 includes the following components:

Feed concentrate (384 million kilograms of nitrogen)

Feed concentrates are used to make livestock feed with a high nutritional value. They are divided into single-ingredient concentrates, such as cereals and pulses, and mixed feed concentrates. Mixed feed is the collective term for dry livestock feeds that are made up of various concentrates. Some are moisture-rich feed concentrates, which are used to make feed with a high moisture content. Feed concentrate is used in pig farming and poultry farming, and also as a supplementary feed for cattle, horses and sheep.

Roughage (input: 260 million kilograms of nitrogen; harvest: 253 million kilograms of nitrogen)

Roughage comprises non-perishable products grown specifically for livestock feed, which undergo no - or little - processing. Examples of roughage include fresh grass, silage, hay and silage maize. Roughage has a relatively low nutrient content per unit of weight. It is used to feed cattle, horses and sheep.

Silage is made from grass that is mown in spring or summer. The mown grass is collected, often in a large pit, and then covered with plastic. Grass can also be packed into plastic bales in the field directly after mowing to make silage. Cattle, sheep, goats, horses and donkeys also graze directly on fresh grass in the field. Hay is grass that has been mown and dried in the sun. It is a form of roughage and can be particularly useful during periods when fresh grass is scarce. There is a clear difference between hay and silage. The latter contains considerably more moisture. The dry matter content of hay is around 85 percent, while silage is around 40 percent dry matter. Fodder maize is maize grown primarily for animal feed; during harvesting, the stalks and unripe cobs are chopped into small pieces, stored in a large heap and left to turn into silage. Cattle and other livestock eat this as roughage. Pigs and poultry do not eat roughage, only feed concentrate.

Change in stocks of roughage (7 million kilograms of nitrogen)

In the case of roughage, there is a feedback loop in the nutrient balance flow chart: nitrogen removed from agricultural land is returned directly to livestock in the form of roughage (silage, pasture grass, hay and fodder maize). In 2023, 283 million tonnes of nitrogen was harvested in the form of roughage. Of this, 267 million kilograms of nitrogen was consumed by livestock in the form of roughage and thereby reused in the agriculture sector, and 16 million kilograms of nitrogen was stored in the form of roughage (in silage bales and silage pits, for example). The difference between what is used and what is harvested is the change in stock level. In 2024, less roughage was harvested due to wet weather conditions, but 253 million kilograms of nitrogen was produced. However, 260 million kilograms of nitrogen was returned to the livestock sector as roughage. In this case, the stock was therefore lower by 7 million kilograms of nitrogen (in the form of bales and silage).

Artificial fertilisers (201 million kilograms of nitrogen)

This is fertiliser that is produced artificially in a factory and can be applied to agricultural land. Artificial fertilisers may consist of a single type of fertiliser (single-component fertilisers) or a mixture (multi-component fertilisers). They are available in solid or liquid form and are used as a soil improver and source of nutrients for crops.

Animal manure (excreted: 449 million kilograms of nitrogen; used on agricultural land: 332 million kilograms of nitrogen)

Manure excreted by cattle, pigs, poultry, horses and ponies, sheep and goats, rabbits and furred animals. The excretion of manure is the process by which livestock produce faeces and urine. Animal manure is usually stored for several months, either inside livestock sheds or outside. For cattle, sheep, horses and ponies, this total includes the amount of manure that these animals produce while grazing outside. It is used as a soil improver and a source of nutrients for crops. The manure produced in livestock sheds is applied to the soil in various ways or stored. The manure produced by livestock in the field ends up directly on the ground.

Sale for non-agricultural use (63 million kilograms of nitrogen)

Some of the manure produced in the Dutch agriculture sector is used outside the sector. For example, it may be used by non-commercial farms, nature reserves or private individuals, or it may be processed and exported abroad (manure imports from other countries are subtracted from manure exports). The majority of animal manure exports go to Germany. Imports of manure are much more limited than exports, and consist mainly of horse manure, which is used in the Netherlands as a substrate for cultivating mushrooms.

Plant products (75 million kilograms of nitrogen)

Nitrogen that leaves the agricultural sector through crop production. This excludes nitrogen that is reused in the livestock sector in the form of roughage (fodder maize, grass, etc.). Plant-based products can be divided into arable crops and horticultural crops. The main arable crops are potatoes, sugar beet and wheat. The main horticultural crops are ornamental plants (i.e. flowers), onions, tomatoes, mushrooms, apples and pears.

Animal products (195 million kilograms of nitrogen)

Nitrogen that leaves the agriculture sector in animal products such as meat, milk and eggs. This excludes manure.

Deposition (Total deposition: 34 million kilograms of nitrogen)

Nitrogen deposition refers to the processes by which the nitrogen in reactive nitrogen compounds in the air is deposited onto soil and into water. Deposition is discussed in further detail in Deposition of nitrogen compounds. For the purposes of the Mineral Balance Flow Chart, this means how much nitrogen is deposited on agricultural land in the Netherlands. The mineral balance flow chart distinguishes between the deposition of nitrogen from agriculture in the Netherlands that is deposited on agricultural land in the Netherlands (19 million kilograms of nitrogen) and nitrogen that comes from outside agriculture in the Netherlands (15 million kilograms; from industry, transport and other countries). A total of 34 million kilograms of nitrogen was applied to agricultural land in the Netherlands in 2024.

Other sources (22 million kilograms of nitrogen)

Nitrogen inputs into arable land that do not originate from animal manure, artificial fertiliser or atmospheric deposition. These include nitrogen that is fixed naturally from the atmosphere (nitrogen can be fixed directly by bacteria living symbiotically in some plants such as peas, alfalfa and clover), compost, seeds and planting stock, sewage sludge (from sewage treatment works) and beet pulp (a by-product of sugar beet processing).

Surplus nitrogen released into the atmosphere (75 million kilograms of nitrogen)

In the Nutrient Balance Flow Chart, the nitrogen surplus released into the atmosphere is calculated by subtracting nitrogen deposition from agricultural sources from nitrogen lost through volatilisation. Nitrogen lost through volatilisation concerns emissions of ammonia (NH₃) and other nitrogen compounds into the atmosphere. In agriculture, the main problem is ammonia emissions, while emissions of other compounds such as nitrous oxide (N₂O) and nitrogen oxide (NO) account for only a small proportion of emissions. Nitrogen emissions are released from livestock sheds and manure in storage; together, these amount to 54 million kilograms of nitrogen. They also occur in the field, when manure in applied and as crops mature; a combined total of 40 million kilograms of nitrogen. These two figures are added together, and deposition of nitrogen from agriculture of 19 million kilograms is subtracted from this in order to determine the surplus nitrogen released into the atmosphere. More information on nitrogen emissions can be found in Nitrogen emissions into the atmosphere; more information on deposition can be found in Deposition of nitrogen compounds.

Surplus nitrogen released into the soil (220 million kilograms of nitrogen)

The nitrogen surplus is the net amount remaining after all nitrogen inputs have been subtracted from nitrogen outputs in agriculture. Inputs include concentrated feed, fertiliser, deposition and a number of other minor sources. Outputs include plant and animal products, and sales of manure (mainly for export). What remains is the total nitrogen surplus (shown in blue and grey in the flowchart). By subtracting the surplus nitrogen released into the atmosphere (shown in blue) from this, the surplus nitrogen released into the soil (grey arrow) is what remains.

Utilisatio

‘Utilisation’ is a word that is frequently used in connection with the nutrient balance. It is defined as the percentage of total nitrogen inputs into agriculture (minus the application of manure outside agriculture) that ends up in animal products (such as meat, milk and eggs) and plant products (vegetables, fruit, ornamental plants).