Field experiments 2020-2021

Small-scale crop growth trials began in 2020

To investigate whether plants are affected by a PRECIKEM treatment, small-scale experiments were commenced in 2020. Two-metre-long tubes with an outer diameter of 315 mm and a wall thickness of 18.7 mm were pressed down into the soil. The length of the tubes thus extended from the surface down to the unoxidized sediment. Smaller tubes were installed inside the bigger tube for the injection of the treatment suspension and for adjusting the groundwater table.

Barley and grass were sown in May 2020 (Fig. 1) and the first treatments were done in June 2020 (Fig. 2). Every treatment was repeated in three different tubes and the treatments were: river water (reference treatment), a suspension of C2 ultrafine-grained limestone (median particle diameter 2.5 µm), cow urine diluted 1:10, and a combination treatment consisting of a C2 suspension followed by a suspension of fine-grained peat (particle diameter < 0.5 mm). The PRECIKEM treatments were injected at drainage depth, 95–115 cm below ground level, while the diluted urine was injected at a depth of 45–65 cm below ground level. The treatments are summarized in Table 1. In three tubes the groundwater table was allowed to sink with evaporation, in all other tubes the groundwater table was maintained by either manually removing groundwater or adding river water. Treatment effects on barley were followed up in the autumn of 2020 by taking the whole above-ground barley plants for drying. Stubble and roots were left in the tubes. After drying, the grain and straw fractions were separated and weighed.

Table 1. A summary of treatments in the crop growth trials. Every treatment was repeated in three tubes, and the trial consisted of 18 tubes in total.

Preparations for large-sale experiments in 2020

The planning and realization of a separate tube for subirrigation in subfields 6 and 9 was successfully completed in 2020. This supplement was planned by Mikael Blomqvist, ProAgria Österbottens Svenska Lantbrukssällskap, who also supervised its construction. The construction work was done by Nybacks Gräv, and the funding was awarded by Svensk-Österbottniska Samfundet. The subirrigation tube lies about 60 cm below ground level, in the upper part of the acidified soil layer underneath the plough layer, and thus about 50 cm above the drainage. The tube is in the form of a loop connected to its own well (see Fig. 9 on the Risöfladan Experimental Field page). As a treatment suspension is pumped through this tube, the suspension flows downward and to the sides through cracks and pores in the soil. This way a larger volume of the acidified soil layer is treated.

A central activity in the ProPRECIKEM project was the introduction of an automated dosing of the limestone powder in the mixing vessel as the treatment suspension was being prepared. Planning started already in 2019 with company visits, but the Covid-19 pandemic delayed the work considerably. Preparations continued in 2020 and separate funding for the equipment was awarded by the Drainage Foundation (Salaojituksen Tukisäätiö) and Handlanden Gustaf Svanljungs Donationsfond. Finally, in 2021, the equipment was constructed by JPT- Industria in Ilmajoki. The equipment, delivered in June 2021, consists of a 300-litres stainless-steel funnel with a vibrator to prevent powder bridging/arching. At the bottom of the funnel, three screws driven by an electric motor transport the powder to the mixing vessel. The speed of the motor and thus the screws is controlled by an AC drive. The limestone powder in big bags were situated on a tractor trailer and a belt conveyor was used to transport the powder to the funnel.

Field experiments 2021

The small-scale crop growth experiments continued in the summer of 2021. The grass sowed in the spring of 2020 continued to grow in the tubes. The treatments were repeated in June 2021, and they were the same as in the previous year. During both seasons, the groundwater table was adjusted to the dam height set in the control wells in the larger field. If the water level was too high water was pumped out, and if the water level was too low river water was added.

The grass was harvested three times during 2021: 21 June, 12 August and in connection with the ending of the experiment 20–22 September. The harvested grass was dried and weighed. As the experiment ended, the tubes were lifted with the help of an excavator and were split (Fig. 3). Samples for geochemical analyses were taken and pH profiles were measured. The stubble and the roots were recovered by rinsing with large amounts of water, for drying and weighing.

The results from the crop growth experiments are being compiled and will be published in a scientific journal.

In the large-scale field experiments in 2021, the new subirrigation tubes were tested for the first time together with the newly developed automated dosing of limestone powder. Subfields 6 and 9 were supplemented in 2020 with separate subirrigation tubes in the form of loops at a depth of about 60 cm below ground level (see Fig. 9 on the Risöfladan Experimental Field page). This level coincides with the upper part of the acidified layer below the plough layer. The acidified layer extends down to the drainpipes at a depth of about 110 cm below ground level. In earlier field experiments, the treatment suspension has been pumped through the drainpipes and has had to rise from there up into the acidified layer. With the new subirrigation tube, the treatment suspension enters the upper part of the acidified layer and flows from there downwards and to the sides. A larger volume of the acidified layer is treated.

The other novelty in 2021 was the automated dosing of limestone powder into the mixing vessel. Earlier this had been done manually. The dosing equipment was integrated with the mixing vessel and a belt conveyor was used to transport the powder from big bags on a tractor trailer to the dosing funnel (Fig. 4). This method and the equipment worked very well during the experiments.

Water for the suspensions was as earlier pumped from the nearby river. The concentration of the suspension was governed by measuring and adjusting the flow of river water, and by adjusting the speed of the screws transporting the limestone powder. Subfield 6 was treated with 660 kg of C2 limestone powder and subfield 9 with 810 kg of C2 limestone powder. As earlier, before and after a treatment the tubes and nearby soil were rinsed with 10 m³ of river water.

Following up the effects of the large-scale field experiments

The quality of the drainage water from all subfields was as earlier followed by sampling spring and autumn during the whole project. The methodology was the same as previously.

In order to detect any possible effect from the treatments on crops, smaller plots on subfields 6 and 9 and the reference subfields were harvested separately in late summer of 2022 by Vesa Hietanen of Ilmajoki. Lodged crops made the conditions difficult. Results in the form of the weight of the dried grain showed no significant difference in harvest between the treated subfields and the reference subfields.

The results from the crop growth experiments are being compiled and will be published in a scientific journal.