Alternative circular fertilisers have a high importance in organic agriculture. Since synthetic mineral fertilisers are not permitted in organic agriculture (EU organic regulation 2018/848) and sources like rock phosphate are not popular, organic farmers heavily rely on alternative circular fertilisers to maintain balanced nutrient levels and ensure soil health.
Many organic arable and livestock farms in most EU countries suffer from negative nutrient balances, particularly lacking Phosphorus (P), which limits production performance. However, Nitrogen (N) availability in soil is not a critical issue because the demand for N can mostly be met by planting legume crops that fix atmospheric nitrogen. While organic farming protocols generally limit the application of N through fertilisation, the same cannot be said for P. Organic farmers need to be more aware of negative phosphorus balances as this can lead to a decrease in production yields over the long term.
To identify nutrient deficiencies, organic farmers can monitor the vigour of legumes; a decrease in vigour is an initial warning sign. When nutrient deficiencies appear, organic fertilisers like biogas digestate are ideal sources for both P and N, helping to build regional nutrient cycles through biogas plants. The local availability of these nutrients can make organic agriculture more sustainable and profitable, thus more attractive to primary sector entrepreneurs.
Compost, on the other hand, usually does not contain high levels of phosphorus, but its low market price makes it a very convenient way to balance soil nutrients. Compost, with some restrictions on the feedstocks and further limitations on a few characteristics, can be effectively used in organic farming thus generating many additional benefits for the soil, such as improving organic matter levels and soil fertility. Spent mushroom substrate is also a valuable soil amendment in organic agriculture, having a similar effect as compost.
Moving to the latest generation of circular fertilisers, recovered struvite (NH4MgPO4·6H2O) offers a new opportunity for many organic farmers to access phosphorus from non-synthetic fertilisers, especially when no P-rich digestate is available regionally. Struvite’s slow release of phosphorus aligns with organic principles and soil health recommendations, making it suitable for organic farming. Its good fertilisation properties have been demonstrated in real field conditions. However, more tests are needed to validate and protocol struvite applications in organic farming environments. Although the European regulatory framework has recognised that struvite meets EU organic standards (EU 2023/121 Implementing Regulation) in January 2023, most organic farmers are still unaware of its characteristics and potential uses.
Feather meal, whether from organic or non-organic poultry livestock, is a niche organic fertiliser currently mostly used in organic horticultural crops.
As for sewage sludge, a circular fertiliser whose use in agriculture varies among EU member states, it is not permitted in organic agriculture.
For more information about the impact assessment of the aforementioned circular fertilisers, don’t miss the FER-PLAY report on the “Multi-assessment of impacts, trade-offs and framework conditions,” available from September 2024 in the Resources section of the FER-PLAY website.
