Gypsum treatment of fields enhances water protection in agriculture

25.5.2018
Gypsum treatment of agricultural fields has proven to be a safe and effective method, approved by farmers, in reducing phosphorus load originating from agriculture to the Baltic Sea. The results are based on a large-scale pilot project testing the application of gypsum to agricultural fields in Southwest Finland. Large-scale use of gypsum would enable Finland to meet the goals set by the Baltic Marine Environment Protection Commission (HELCOM) for reducing the phosphorus load entering the Baltic Sea. Gypsum treatment would have extensive potential throughout the Baltic Sea area.

In the autumn of 2016, gypsum was applied to over 1,500 hectares of agricultural land in the River Savijoki catchment area in ​​Southwest Finland. The effects of gypsum have been monitored both in the fields and in river water.

“Monitoring of water quality in the River Savijoki confirms the results of previous studies: the phosphorus load from fields is reduced by 50%,” says Senior Researcher Petri Ekholm from the Finnish Environment Institute.

In order to prevent eutrophication, it is important to reduce not only particulate phosphorus but also dissolved phosphorus, which is immediately available for algae. Gypsum reduces the both forms of phosphorus effectively and quickly. The effect of one application lasts for around five years.

Because gypsum is easily dissolved, the sulphate in gypsum (CaSO4 H2O) slowly leaches into water bodies. Both monitoring and laboratory analyses have, however, shown that sulphate concentrations measured in river water do not adversely affect the threatened thick-shelled river mussel (Unio crassus), trout (Salmo trutta) or greater water moss (Fontinalis antipyretica).

Gypsum treatment should be promoted in Finland and in the other Baltic Sea countries

It has been calculated that the field area suitable for gypsum treatment in the coastal areas of Southern Finland amounts to around 540,000 hectares. Preparations for the introduction of gypsum treatment could be made in this area. The treatment fits smoothly into farming practices. It does not decrease the cultivated area or yields, but may make soil cultivation easier. 

In Finland, gypsum treatment would reduce phosphorus load by 200–300 tonnes per year, and in the Baltic Sea as a whole by 1,500 to 2,000 tonnes per year. “It costs about 70 euros to reduce one kilo of phosphorus by using gypsum, while the other methods available for agriculture would cost around 220 euros,” says Professor Markku Ollikainen from the University of Helsinki.

Based on the pilot, a proposal will be drafted for the inclusion of gypsum treatment on the list of recommended and nationally supported water protection methods. Gypsum treatment would increase the cost-effectiveness of Baltic Sea protection, if it were included in the pool of methods, for example, at EU level. 

 

 

EU Interreg NutriTrade 450

 

 

 

 

Petri Ekholm

Senior Researcher, Finnish Environment Institute SYKE

Eliisa Punttila

Project coordinator

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