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), which form arbuscular mycorrhiza (AM), help crops to absorb nutrients (especially phosphorus) that are immobile in the soil. 

These type of 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 were subjected to laboratory analyses, incubation  and pot tests in controlled environment and in greenhouses in order to assess their effectiveness and impact on plant growth, health and yield. 
  • Both inorganic and organic industrial residues (oil shale ash, biochar,  meat-and-bone meal) were used in fertiliser preparations. As binders, we targeted food industry by-products to raise value by recycling inputs.
  • Production tests and field demos were carried out with the most promising fertiliser recipes. The effect of  prototype fertilisers was evaluated in production trials.
  • Agrotechnical experiments, as well as the cost-efficiency analysis was part of the study as it’s important to offer the farmer the most economically viable solution.
  • The aim of this work was develop novel fertilizers and test their impact on the soil, plant yield, the environment.

Cultivation of mycorrhizal fungal inocula in the laboratory of the University of Tartu. The isolates were grown in trap cultures on corn. To select isolates with high potential, isolates were grown in permanent cultures with maize plants (top). In a later stage of the project, experiments were carried out in a greenhouse under artificial light to test the interaction of isolates with the pellet (wheat, below).

inocula, mycorrhizal fungi experiment
pot experiment, fertilisers


  1. Appropriate ratios of feedstock materials and parameters of the granulation process were developed at NICPB. To optimise the production process, drying speed, strength, durability of the granules were determined and the water solubility tests of the pellets were performed. 
  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 other 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, isolated with higher potential were selected to be tested within the product development process. 
  5. In wet granulation process, fungal mixtures can be added during the process, but we learned that these fungi are very temperature sensitive. Longer drying times reduce productivity and require the use of a larger dryer under production conditions. Other option is to inoculate the pellets after granulation.
  6. Of the organic feedstocks, meat-and-bone meal in particular gave good results. The use of different sulphate salts in the recipe facilitated the granulation process. In the case of biochar, the low moisture content of the material was a disadvantage.
  7. Despite regulatory restrains for usage in organic farming, test results showed oil shale ash-based fertilisers have a positive effect on especially acidic soils. We observed an increase in biomass  yield of grasses, and enhancement in valuable soil nutrients.
  8. Pellets no more than 5 mm in length can also be spread with a combination spreader.
  9. In the wheat trial, the biomass of the straw/shoots and roots was mainly affected by the addition of granules, independent of the bioactive fungal particles. Spikelet mass was significantly higher in treatments where a combination of granules and AM fungi was added, both in sterile and in standard soils. 
  10. The addition of AM fungi without granules did not have a significant effect on plant biomass, but did increase root colonization which may support plant pathogen resistance.

Solubility is key to deliver all important nutrients to plants. Photo above depicts water solubility testing in NICPB for our prototype fertilisers.

The project also involved cooperation with the VTT Centre for Technology Research (Jyväskylä, Finland). For the field trials, fertilisers were produced in the Ismo Tiihonen Sprout Matador fertiliser plant with a capacity of about 100-300 kg/hour. 

Results indicate we have found good recipes for fertilisers that are effective and suitable for local soil conditions. The prepared lime fertiliser formulations are effective and can be used as soil pH modifiers. Using bioacive agents in form of mycorrhizal fungi is not only novel but functional. The inoculum’s effect on plant yields was best when used in combination, together with granules, in a mixed formulae when added to soils. 

Approximately a quarter of a tonne of inoculates of two different types were produced in the UT greenhouse for the field trials. In an additional test, the surface of the granulated pellets was coated with fungal inocula (photo below). 

Why is it important to develop fertilisers that comply with the principles of the circular economy? Thanks to the research work, it is possible to offer efficient and easily available alternatives for the local producer. These alternative fertilisers play a strategic role in transition for more environmentally friendly management.

New knowledge about the effects of organic fertilisers on plant nutrition and health will help organic farmers to make more informed choices about inputs. The economic benefits for farmers will come from increased crop production efficiency, based on a better knowledge of soil conditions. 

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