What are organic fertilizers?

In short: organic fertilisers are fertilisers made from organic matter – plant or animal – such as compost, vermicompost, pelleted manure and poultry litter, guano, and blood, feather, bone or fish meal. They supply plants with nitrogen, phosphorus, potassium and micronutrients while adding humus to the soil and improving its structure. Their nutrients are released slowly as the organic matter decomposes. Polish legislation distinguishes them from natural fertilisers (farm manures: solid manure, slurry and liquid manure straight from the farm), and they differ from mineral fertilisers in, among other things, their variable composition and slower action. The best results usually come from combining organic and mineral fertilisation.

What are organic fertilisers?

Organic fertilisers are products made from organic substances of plant or animal origin that supply plants with nutrients and improve soil properties. They contain organic carbon, from which humus forms in the soil, as well as macronutrients (nitrogen, phosphorus, potassium, calcium, magnesium, sulphur) and micronutrients (including iron, manganese, zinc, copper, boron and molybdenum).

The nutrients in organic fertilisers are largely bound in organic matter. Plants can take them up only after soil microorganisms have broken this matter down, which is why organic fertilisers act more slowly, but for longer, than mineral fertilisers.

In the EU, the requirements for organic fertilisers placed on the market are set out in the Fertilising Products Regulation (EU) 2019/1009. A solid organic fertiliser must contain, among other things, at least 15% organic carbon and a declared minimum content of nitrogen, phosphorus or potassium. Fertilisers may also be authorised for the domestic market under national rules.

How do organic fertilisers differ from natural fertilisers (farm manures)?

In everyday language the two terms are used interchangeably, but the Polish Act on fertilisers and fertilisation draws a clear distinction between them:

• natural fertilisers (farm manures) – solid manure, slurry, liquid manure and poultry droppings produced on the farm and intended for agricultural use without processing; they do not require market authorisation, but their use is restricted by, among other things, nitrates rules,
• organic fertilisers – products made from organic substances or their mixtures, e.g. compost, pelleted manure and poultry litter, animal meals, vermicompost; when placed on the market they must meet quality requirements and have a declared composition.

Pelleted manure bought at a garden centre is therefore an organic fertiliser, whereas manure from a heap on a farm is a natural fertiliser.

What types of organic fertilisers are there?

Organic fertilisers are most often classified by the origin of the raw material. Their composition varies and depends on the raw material and how it has been processed.

Organic fertilisers of animal origin

This group includes:

• processed manure and poultry droppings – composted, dried and pelleted, free from unpleasant odour and weed seeds,
• guano – the droppings of seabirds or bats, very rich in nitrogen and phosphorus,
• vermicompost (worm castings) – organic matter processed by red wiggler earthworms, with a good structure and gentle action,
• animal meals – blood meal (a fast-acting source of nitrogen), feather meal (slow-release nitrogen), bone meal (phosphorus and calcium) and fish meal (nitrogen, phosphorus, micronutrients).

Animal meals are processed animal by-products, so they are subject to EU animal by-product rules – they must undergo appropriate treatment, and livestock must not be grazed on pasture fertilised with such products for at least 21 days. We cover the individual meals in the articles Fish meal: how to use it as an organic fertiliser?, Blood meal – overview and Feather meal – overview.

Organic fertilisers of plant origin

The most important plant-based fertiliser is compost – plant matter (leaves, grass, vegetable and fruit scraps, branches) broken down by microorganisms. This group also includes composted bark and sawdust, pomace and stillage from the food industry, seaweed fertilisers and green manures – plants such as lupin, white mustard or phacelia, grown in order to be ploughed in to enrich the soil with organic matter.

Approximate nutrient content of popular organic and natural fertilisers:

Fertiliser	Nitrogen (N)	Phosphorus (P₂O₅)	Potassium (K₂O)	Action
Cattle manure (fresh)	approx. 0.5%	approx. 0.3%	approx. 0.7%	slow, improves soil structure
Pelleted chicken manure	approx. 3–4%	approx. 2–3%	approx. 2–3%	relatively fast
Compost	approx. 0.5–1.5%	approx. 0.3–1%	approx. 0.5–1%	slow, high in humus
Vermicompost	approx. 1–2%	approx. 1–1.5%	approx. 1–1.5%	gentle
Blood meal	approx. 12–13%	trace	trace	fast source of nitrogen
Feather meal	approx. 12–14%	trace	trace	slow nitrogen release
Fish meal	approx. 8–11%	approx. 4–6%	approx. 1%	moderately fast
Bone meal	approx. 3–5%	approx. 15–20%	trace	slow source of phosphorus and calcium

The actual composition depends on the raw material and the technology used – always check the manufacturer’s declaration when buying.

How do organic fertilisers differ from mineral fertilisers?

Mineral (synthetic) fertilisers are industrial products with a precisely defined nutrient content in forms readily available to plants, e.g. ammonium nitrate, urea, superphosphate or muriate of potash. The main differences:

Feature	Organic fertilisers	Mineral fertilisers
Origin	plant and animal matter	chemical synthesis or mined raw materials
Nutrient content	low to medium, variable	high, precisely defined
Speed of action	slow, spread over time	fast
Effect on soil	increases humus, improves structure and biological activity	supplies no humus; misuse can acidify the soil
Application rates and transport	large quantities, costly transport (except meals and pellets)	small rates, easy to transport and spread
Risk of nutrient losses	nitrogen leaching if applied at the wrong time, ammonia emissions	leaching when over-applied

Bear in mind that urea is an organic compound, but as a fertiliser it is a synthetic product and is classed as a mineral nitrogen fertiliser – read more in the article Benefits of using urea as a fertiliser.

Can organic and mineral fertilisers be combined? Yes – this is the most common and recommended practice. Organic fertiliser builds soil fertility, while mineral fertiliser tops up nutrients when crop demand is highest. When planning application rates, the nutrients supplied with the organic fertiliser must be taken into account. However, manure should not be mixed or applied at the same time as lime, as this causes large nitrogen losses in the form of ammonia.

What are organo-mineral fertilisers?

Organo-mineral fertilisers are products in which organic matter (e.g. compost, peat, lignite, leonardite, poultry manure or animal meals) is combined with mineral fertilisers. They combine the advantages of both groups: they supply humus-forming organic matter as well as readily available nutrients in defined amounts.

Under the EU Fertilising Products Regulation, a solid organo-mineral fertiliser must contain at least 7.5% organic carbon and declared amounts of nutrients. It usually comes as granules, which are easy to apply with a fertiliser spreader. Organo-mineral fertilisers are used in vegetable growing, orchards, nurseries, on lawns and in gardens, as well as for pre-sowing fertilisation of field crops.

How and when should organic fertilisers be applied?

The method of application depends on the type of fertiliser, the crop and the soil. The key principles:

• soil analysis – before fertilising, it is worth checking nutrient content and pH to avoid over-fertilising the soil,
• timing – manure and compost are most often applied in autumn ahead of spring crops or in early spring; pelleted fertilisers and meals before sowing or planting and as a top dressing,
• rapid incorporation into the soil – manure and ammonia-containing fertilisers must be ploughed in or mixed into the soil as soon as possible after spreading to limit nitrogen losses,
• rates – manure usually every 3–4 years at 20–40 t/ha; in the garden, compost at 3–5 kg/m²; meals and pellets according to the manufacturer’s recommendations,
• regulations – natural fertilisers may supply no more than 170 kg of nitrogen per hectare per year; closed periods for fertilising also apply, as does a ban on application to frozen, waterlogged or snow-covered soils.

In home gardens, organic fertilisers work well for vegetables, fruit trees and bushes, ornamental plants and lawns. Vermicompost is most commonly used for pot plants.

What are the advantages and disadvantages of organic fertilisers?

Advantages:

• they increase humus content and improve soil structure and its capacity to retain water and nutrients,
• they support soil biology – microorganisms and earthworms,
• they release nutrients gradually over a longer period,
• they make use of waste and by-products from agriculture and the food industry,
• many of them are permitted in organic farming.

Disadvantages:

• variable and relatively low nutrient content, which makes precise fertilisation difficult,
• slower action – they may not meet crop demand during periods of intensive growth,
• large application rates and transport costs in the case of manure and compost,
• odour and the risk of pathogens and weed seeds if the fertiliser has not been properly processed,
• risk of nitrogen leaching and ammonia emissions if applied at the wrong time or in the wrong way.

Organic fertilisers are therefore not automatically “safe” – they too can over-fertilise the soil and pollute water with nitrates.

Can organic fertilisers be used in organic farming?

Yes, but only those listed in the EU organic production rules. Permitted inputs include manure and poultry droppings (except from factory farming), compost, vermicompost, guano, blood, hoof, horn, bone, feather and fish meal, as well as certain natural mineral raw materials, e.g. ground rock phosphate or lime.

Synthetic nitrogen fertilisers, including urea and ammonium nitrate, may not be used in organic farming. An organic farm should base its fertilisation primarily on crop rotation, legumes, green manures and natural fertilisers (farm manures) from its own holding.

How do you choose an organic fertiliser?

When choosing an organic fertiliser – whether for a farm or for fertiliser production – it is worth considering:

• composition – the content of nitrogen, phosphorus, potassium, organic carbon and micronutrients, matched to soil analysis results and crop needs,
• form – powder, granules, pellets or liquid; granules are easier to spread and store,
• safety – sanitisation (no pathogens or weed seeds) and heavy metal content within limits,
• market authorisation – compliance with the EU Fertilising Products Regulation or a national authorisation and, for organic crops, approval for use in organic farming.

Foodcom supplies fertiliser and feed manufacturers with raw materials of organic origin, including fish meal, feather meal and blood meal, as well as mineral fertilisers such as urea. For specifications and availability, contact our sales team.