Field experiments 2016-2017
Field experiments 2016-2017
In the PRECIKEM II project, two new treatment chemicals and a system for a circulating subirrigation were taken into use. The ultrafine-grained and surface-modified product Enrich Bio developed by Nordkalk is a pure precipitated calcium carbonate. The dispersing agent is necessary in order to reach a median particle diameter of 0.3 µm, and the dispersant is biodegradable and environment friendly. The product was delivered as a concentrated suspension with a CaCO3 content of 37 %, and it was diluted to the desired concentration with river water in the field. The final suspension was expected to be very stable, and the extremely small particle size made it possible to reach and treat large parts of the porous and heterogeneous surfaces of hydrologically active cracks and macropores in the soil.
The use of peat was another novelty in these experiments. In the laboratory experiments, it had been found that fine-grained peat adsorbs onto surfaces of the macropores in the soil that are reachable by a treatment suspension. When peat is adsorbed, four different effects were anticipated:
1) Peat functions as an antioxidant and protects the sulfides in the soil by being oxidized and thus consuming oxygen as air is entering the macropores of the soil during dry periods.
2) Reducing conditions are created at the macropore surfaces.
3) Reducing bacteria can use peat as an energy source.
4) The peat forms complexes with, and thus immobilizes, dissolved metals.
The experiments involving peat were combination treatments. i.e., the treatment consisted of two stages where a C2 limestone suspension (median particle diameter 2.5 µm) was introduced first and then, as a second stage, followed by a peat suspension (particle diameter < 0.5 mm).
The field experiments 2012–2014 had resulted in some sedimentation further out in the drainage pipes, these being cul-de-sacs, as the subirrigation flow approaches zero. Therefore, a new type of drainage without dead ends and allowing for a circulating subirrigation flow with an even flow and pressure in the whole system, was developed in the project. Planning and supervision of the construction of the new drainage system was carried out by Rainer Rosendahl, ProAgria Österbottens Svenska Lantbrukssällskap. Three new subfields, no. 10, 11 and 12, were constructed with the new drainage in the autumn of 2016 by Nybacks Gräv. The work was funded by the Drainage Foundation (Salaojituksen tukisäätiö). The principle of the drainage system is shown in Fig. 6 on the Risöfladan Experimental Field page.
Water for preparing the suspensions was taken as previously from the nearby river. The flow measurements, the preparation of the suspensions, and the rinsing of the drainage system with 10 m3 of river water before and after treatments were all done as in previous experiments.
In the summer of 2016, subfields 1 and 8 were treated with 660–820 kg of the ultrafine-grained limestone C2 (earlier product name FC2,5; median particle diameter 2.5 µm). These subfields had previously been treated with slaked lime (calcium hydroxide) and the intention was now to compare the previous treatment with the treatment with a buffering substance such as limestone (calcium carbonate). River water was pumped to the reference subfields 2, 4, and 7.
In the summer of 2017, two different experiments were performed. Subfields 3 and 5 were treated with 610–690 kg of CaCO3 in the form of Nordkalk’s product Enrich Bio calcium carbonate suspension (median particle diameter 0.3 µm). This is a new product, and the purpose of the experiments was to see whether the effect and spread of the treatment in the acidified soil layer could be improved. The new subfields 10 and 12 were first treated with 550–570 kg of C2 ultrafine-grained limestone (median particle diameter 2.5 µm), after which they were treated with 160 kg peat (particle diameter < 0.5 mm), see Figs 2 and 3. River water was pumped to the reference subfields 2, 4, 7, and 11.
Follow-up measurements of drainage water quality
As earlier, the effects of the treatments were followed by sampling the drainage water from all subfields spring and autumn. The sampling and analysis methods were as earlier. A detailed analysis of the results has been made 2022 by Fanny Ahonen in a master’s thesis at Åbo Akademi University. The results will also be published in a scientific journal.
Follow-up measurements of soil
Late summer 2018 several trenches were dug at Risöfladan to investigate treatment effects on the soil. Subfield 5 (treated with 770 kg of FC2,5 in 2012 and 690 kg of Enrich Bio CaCO3 in 2017), subfield 10 (treated with 550 kg of C2 plus 160 kg of peat in 2017), and subfield 11 (reference field receiving only river water in 2017), were investigated. In total, 21 soil samples were taken in subfield 5, 30 soil samples taken in subfield 10, and 12 soil samples taken in subfield 11, for microbiological analyses. Within four days of the sampling, DNA was isolated using an indirect method from the soil samples. The 16S rRNA gene was PCR-amplified and the samples sent for sequencing. At the same time, samples for geochemical analyses were taken, and leaching experiments as well as pH and acidity measurements were done.
The results will be published in a scientific journal.
