Incubations with homogenized soil samples 2017-2019

Incubations with homogenized soil samples 2017-2019

The aim of the study was to screen the geochemical and microbial effect of ultra-fine grained limestone powder (2.5 µm in diameter, Nordkalk´s product C2) and precipitated calcium carbonate (0.3 µm in diameter, Nordkalk´s product Enrich Bio) and of electron donors in form of organic material (such as peat and various peat degradation products) on acid sulfate soil in both oxygen-rich and oxygen-free environments.

The soil used in the experiment was taken in April 2017 from an untreated reference field by pressing 1.5 m long pipes into the ground with an excavator (Figure 1). In the experiment, the acid sulfate soil layer was used at 75–90 cm.

The different treatments of the homogenized acid sulfate soil were manual mixing of 1) 1 % ultrafine-grained limestone powder (Enrich Bio); 2) 1 % mixture of equal parts peat (H1 level1) and ultrafine-grained limestone powder (C2); 3) 1 % mixture of equal parts peat (H5 level) and ultrafine-grained limestone powder (C2); 4) 0.1 % sodium acetate and 5) 0.1 % natriumlactate per dry weight soil. As a control, untreated soil was used. To investigate the oxygen influence of the treatments, all samples were prepared in both oxygen-free and oxygen-rich environments. All treatments were also performed in three replicates, i.e., three different soil samples taken several meters apart, and different sets of samples for the geochemical and microbiological analyzes were used. After treatment, the soil samples were stored at 10 °C in the dark for 10 weeks.

After incubation, the pH of the geochemical samples was measured and then frozen at -20 °C. From the thawed samples, sulfur and iron speciations were performed, as well as an analysis of selected metals. For the microbiological analyses, DNA was isolated from intact bacterial cells leached from the soil samples. From the isolated DNA, the 16S rRNA gene was PCR-amplified2 in order to identify the bacteria. After the PCR amplification, the samples were sent for sequencing, after which in-depth data analyses of the sequence material were performed to identify the bacterial populations in the untreated and treated soil samples. The compiled sequencing and geochemical data were published in 2020 in the journal Soil Ecology Letters in the article Biodegraded peat and ultrafine calcium carbonate result in retained metals and higher microbial diversities in boreal acid sulfate soil.