Organic fertilisers and the potential of biochar

The aim is to reduce the environmental impacts of organic fertilisers

The use of organic fertilisers can lead to greenhouse gas emissions,  nutrient leaching problems, groundwater pollution and cause unpleasant odor. The loss of nutrients through volatilisation and leaching reduces the profitability, as additional use of mineral fertilisers is required to maintain soil fertility. We are testing adding of biochar to liquid manure to reduce the loss of nutrients. The impact of biochar on nitrogen (N) and carbon (C) emissions, leaching of nitrogen compounds, soil carbon stock and crop yield will be assessed within this study. 

The root zone of plants is the area of soil and oxygen surrounding the roots of a plant. Roots are the starting point of a plant’s vascular system. Water and nutrients are pulled up from the oxygenated soil around the roots, called the root zone, and pumped into all the aerial parts of the plant.

  • Adding biochar to liquid manure is technologically easy and spreading of manure enriched with biochar does not require specific equipment.
  • Biochar is added to liquid manure to adsorb N and C and reduce the mobility and loss of these compounds.
  • Biochar binds NH4-N and carbon dioxide from the liquid manure digestate, thereby reducing N and C emissions. In soil, carbon is sequestrated, it slows down the movement of water and binds to NO3-N ions.
  • In carbon-enriched soil, nutrients remain longer in the root zone of plants. Biochar also enriches the soil with stable carbon. 

The effectiveness of biochar in reducing N leaching is compared with other agronomic techniques used for the same purpose: growing catch crops, mixing liquid manure with straw and using different tillage methods after the manure application e.g fertilisation. This gives farmers the opportunity to implement the option that suits them best. The experiments are planned to be carried out in the period 2017 (May) to 2020 (August)  on lysimeters at the Estonian University of Life Sciences (Rõhu katsejaam) to evaluate N leaching, and at cluster members’ production fields, where the effect of agronomic techniques on nutrient movement in soil is compared.

In 2017, a lysimeter test was set up, measurements take place in the autumn-winter period. The aim is to compare N and C leaching and emission with regards to the time of application of liquid manure to the soil (August, September, October, November), but also assess the adjuvants used (2 types of biochar, straw and catch crop).

In 2018, experiments were established on production fields, from which the vertical movement of NO3-N compounds in 1 m soil profile on different test patch fields. 

In 2019, experiments continued on the production fields and on lysimeters. We set up a new field test at Meer, where we continued to monitor the movement of NO3-N on different test plots.

In all three years, 215 g of liquid manure was applied to one lysimeter, which corresponds to the standard of about 30 tons per hectare. Immediately after spreading, the liquid manure was mixed with a shovel to a depth of about 10 cm in soil. The control variant did not receive liquid manure, but in the spring it was fertilised with mineral fertiliser similarly to other variants.


The straw was mixed with the soil in all three experimental years.  The biochar was mixed into the liquid manure just before it was applied to the soil in September, October and November, respectively. Biochar added was produced at different temperatures (500 ° C, 1000 ° C). Straw and catch crops were also tested as a fertiliser component – in the first year, Vicia villosa. ‘Villosa’, in another whirlwind (Phacelia tanacetifolia) s. ‘Stala’ and the third pasture ryegrass (Lolium perenne) s. ‘Raite’.

The aim of the study was to evaluate the effect of liquid manure application time and carbon-rich materials (biochar and straw, in picture above) on nitrogen leaching and N-compounds, methane and CO2 emissions in autumn and to compare it with the cultivation of trapping crops.
Photos below show field tests carried out with biochar.

  1. Of the various materials tested, only biochar produced at 1000 ° C reduces nitrogen (N) leaching. 
  2. N leaching is reduced only when biochar is mixed with soil, but results indicate its effect to be poor compared to using catch crops.
  3. Nitrogen leaching does not depend on the time when liquid manure is applied to the soil in autumn. Test results show that even in the case of application executed in mid-November, the leaching of nitrogen is not higher compared to manure application in August, September and October.
  4. In case of a rainy autumn, a lot of N is also leached in the organic form (in the composition of organic compounds). Manure contains about 50% of N-bound organic compounds. Leaching in organic form means leaching of an organic compound containing N (e.g. an amino acid). NO3-N, NH4-N are mineral forms of nitrogen.
  5. The catch crop cultivated after liquid manure application does not significantly reduce the vertical movement of NO3-N in the soil. Nor does biochar, nor the catch culture and biochar together.
  6. Phosphorus (P) leaching was not increased by liquid manure fertilisation alone. However, application of liquid manure with straw or biochar increased the concentration of P in the soil. 
  7. Liquid manure fertilization increases methane (CH4) and carbon dioxide (CO2) emissions from the soil. Most of these gases were emitted when liquid manure was given with straw.
  8. Biochar had no plausible effect on CH4 and CO2 emissions. Fertilisation with liquid manure did not increase NH3-N and N2O emissions.

The photos show the tests performed on lysimeters at Rõhu (May 2017 – August 2020).

In terms of climate, the three experimental years have been very different, which has provided a good overview of how the leaching of nitrogen compounds depends on precipitation.

See final report (EST)

Estonian Universirty of Life Sciences – Henn Raave, Alar Astover
University of Helsinki – Priit Tammeorg, Jure Zrim