PRECIKEM II 2015-2018

The duration of the project was from 1 July 2015 until 31 December 2018.

In the previous PRECIKEM project (2010-2014), it was concluded that there is a need for adjusting not only the pH but also the redox potential of the groundwater of an acid sulfate soil. The pH together with the redox potential govern which chemical form of, e.g., iron and sulfur will dominate. To this objective, fine-grained peat was used on its own or in combination with ultrafine-grained calcium carbonate (limestone) in laboratory experiments and large-scale field experiments at the enlarged experimental field at Risöfladan. The goal was also to further develop the drainage and subsurface irrigation (subirrigation) technique as well as a deepened focus on the microbiology. A continuation of the monitoring programme, which was initiated in 2012, for the drainage waters at Risöfladan was made possible for a further three years by the PRECIKEM II project.

In this project, a further development, both in laboratory and field, of the techniques introduced in the previous PRECIKEM project was accomplished.

In the autumn of 2016, three new 1-hectare subfields were added to the experimental field at Risöfladan. The drainage system in these subfields was of a new design allowing for a circulating subirrigation. This was accomplished by connecting the far ends of the drainpipes to a return pipe thus allowing the irrigation water to return to control well. This way an even pressure and flow is achieved in the whole system and the dead ends of the drainpipes in a conventional drainage are avoided. The first treatment experiments with a circulating system were made in August 2017. The treatment flow was clearly improved, and this technique should also make a conventional subirrigation more effective.

The same limestone quality as in the previous PRECIKEM project was used, i.e., Nordkalk’s C2 (previously named FC2,5) where the median particle diameter is 2.5 µm. Nordkalk’s Enrich Bio was also used in two subfields. This product is a precipitated calcium carbonate with a median particle diameter of 0.3 µm. The particles have been treated with a surface-active substance allowing extremely stable suspensions to be created. The expectation was that these suspensions would easily enter also smaller soil pores.

The field trials in 2017 comprised not only pure limestone treatments but also experiments with a peat suspension. Two subfields were first treated with limestone (Nordkalk’s C2) suspension and directly afterwards with a fine-grained (< 0.5 mm) peat suspension. The peat functions as an antioxidant as the peat is oxidized before the sulfides and thus consumes the oxygen that has penetrated down to the soil layer at drainage depth. Peat is also an energy source for iron- and sulfur-reducing microbes. Furthermore, peat can form complexes with metals dissolved in pore water. This would reduce the possible toxicity of the metals but could also increase their mobility.

In the laboratory, the column leaching experiments with undisturbed soil samples initiated in the previous PRECIKEM project were continued but with a new experimental setup. Instead of the hydrostatic pressure used earlier for transport of treatment solutions and suspensions through the soil sample, membrane pumps were used to achieve a constant flow rate. Further, the whole setup was placed in a refrigerator at 10 °C which reflects the mean temperature in the partially oxidized soil layer at drainage depth. The treatment effects on microbe populations were investigated systematically. To avoid contamination only autoclaved (steam sterilization at 120 °C) water was used in the experiments. After an experiment, the soil sample is kept airtight in a refrigerator at 10 °C for four weeks. After this incubation, samples were taken separately from exposed surfaces and from inner parts of the compact soil material that had not been in direct contact with macropores.

The enlargement of the experimental field at Risöfladan was planned and its construction supervised by Rainer Rosendahl at Österbottens svenska lantbrukssällskap/ProAgria.

Funding
The funding for the project was in total 500 000 € which was granted by the Centre for Economic Development, Transport and the Environment in Ostrobothnia, Finland, from the Rural Development Programme for Mainland Finland 2007-2013 as part of the European Agricultural Fund for the Rural Development.

Funding for the fine-grained peat and chemical analyses was granted by Aktiastiftelsen i Vasa. Funding for Prof. Paweł Nowak’s participation in the interpretation of the experimental results was granted by Aktiastiftelsen i Vasa together with Stiftelsen Handlanden Gustaf Svanljungs Donationsfond. The Drainage Foundation granted funding for the enlargement of the experimental field at Risöfladan. Oiva Kuusisto Säätiö granted funding for Prof. Mark Dopson’s participation as an expert in the microbiological work. Prof. Paweł Nowak is active at the Polish Academy of Sciences in Kraków, Poland, and Prof. Mark Dopson is with the Linnaeus University in Kalmar, Sweden.

Uponor Infra (previously KWH Pipe) and Nordkalk supported the project with material and expert advice.