Granular Organic Fertilisers

Project activities focus on the development of two types of organic fertilisers

Arable soils in Estonia tend to be acidic, have a low humus content and poor biodiversity levels. To reduce these shortcomings, we are developing innovative granular fertilisers based mainly on the recovery of industrial waste. The aim is to improve plant nutrition, ensure higher and more stable yields and a smaller ecological footprint per production unit.

In the framework of this project, together with research institutions we are developing and testing two types of organic fertilisers:

  1. Lime-based granular fertilisers enriched with essential soil nutrients
  2. Granular organic fertilisers enriched with fungi (Glomeromycota)

Soil microorganisms like Rhizophagus irregularis (photo in right), which form arbuscular mycorrhiza (AM), help crops to absorb nutrients (especially phosphorus) that are immobile in the soil. 

These mycorrhizal fungi also increase plant  tolerance to stress  caused by exceptional weather conditions (drought, heavy rains etc) and improve their pathogen resistance.  

Rhizophagus irregularis under microscope.

Preparation of test batches of prototype fertilisers for lab and pot tests at National Institute of Chemical Physics and Biophysics (NICPB) using their granulator.

Granulation is the process by which a powder or other bulk material is bonded into particles of 1-10 mm in size by means of a binder. The added value lies in the enrichment of the  granules with  nutrients, microorganisms and other adjuvants that improve soil quality.

The requirements for these pellets also depend on the production technology. The granules must remain stable from the time they are prepared until they reach the soil. The aim is to make the active substances in the pellet available for plants and for soil organisms. Fertilisation efficiency depends on the way in which the pellets are spread economically per unit area of ​​the field – both with even and location-based spreading techniques.

Granular organic fertilisers help expand and provide choice alternatives for farmers, improving plant nutrition and yields. In addition, they offer greater flexibility in terms of transport, spreading and application. All this reduces risk of soil trampling, nutrient loss and leaching problems. Granular fertilisers have a long-term effect, which makes it possible to save time and lessen workload, e.g. rounds of fertilisation in crop rotation, and also reduce trampling the soil.


  • Prototypes of fertilizers are subjected to laboratory analyses, incubation  and plant tests in controlled environment and in greenhouse in order to assess their effectiveness and impact on the environment. 
  • Both inorganic and organic industrial residues are used as  in fertiliser preparations. By-products of the food industry are mainly tested as binders.
  • Next, with the most promising prototype fertilisers production tests and demo experiments are carried out.
  • The effect of  prototype fertilisers are evaluated in field and production trials.
  • Agrotechnical experiments, as well as the cost-efficiency analysis is carried out to find the most economically viable solution for the farmer. 
  • The aim is to find out the impact of new fertilizers on the yield of organic crops, the soil, the environment, and to assess their profitability.

The photos above show the cultivation of mycorrhizal fungal inocula in the laboratory of the University of Tartu. The isolates were grown in trap cultures on corn. Of these, fungal strains with high potential were selected. 


  1. Appropriate ratios of feedstock materials and parameters of the granulation process were developed at NICPB. To optimize the production process, drying speed, strength, durability of the granules were determined and the water solubility tests of the pellets were performed (photo shown on the right). 
  2. In order to guarantee the development of a lime-based fertiliser suitable for organic farming, alternative materials in addition to oil-shale ash have also been included in the research.  
  3. For fertilisers inoculated with mycorrhizal fungi, isolates were obtained from the University of Tartu and their partners. 24 species and 35 isolates were pooled for the selection process. 
  4. After cultivation of corn under sterile conditions, root colonization with  micro-fungi was determined. In addition, fungal spores were counted from the soil. As a result of the experiment, potential isolates have been selected to be tested within the product development process. 
  5. In wet granulation, fungal mixtures can be added during the process, but it must be taken into account that fungi are very temperature sensitive. Longer drying times reduce productivity and require the use of a larger dryer under production conditions.
  6. The test results show that  oil shale ash-based fertilisers have a positive effect on especially acidic soils, increasing biomass yield of grasses and soil nutrient content.
  7. The prepared fertiliser formulations are effective and can be used as soil pH modifiers.

The planned laboratory and pot tests have been carried out and their initial results have been taken into account for product development.  Results indicate we have found good recipes for fertilisers that are effective and suitable for local soil conditions. 

Know-how on the effect of organic fertilisers on plant nutrition and crop quality will help organic producers in decision-making process. The economic benefits for farmers will be an increase in the efficiency of crop production. At the same time, the use of innovative but easy-to-use local organic fertilisers is important,  as these inputs serve as a prerequisite for environmentally friendly management.

Tooltip content

Estonian University of Life Sciences– Henn Raave, Merike Kissa, Sandra Pärnpuu, Alar Astover, Tõnu Tõnutare
University of Tartu – Tanel Vahter, Maarja Öpik, Surya Mudavasseril Sudheer
Ecolan OY/Ekosovellus Jukka Kivelä – Jukka Kivelä
Estonian Crop Research Insititute – Kalvi Tamm, Taavi Võsa
University of Helsinki – Priit Tammeorg, Niina Välinen, Topi Kopakkala, Mina Kiani, Jure Zrim
National Institute of Chemical Physics and Biophysics  – Janek Reinik
Eesti Energia OÜ – Lauri Laanemäe

Related publications

Should fossil fuel ash be allowed in eco farming? Research in Estonia (Marian Männi), 22.12.2021