FAQ

What are the SAVE and SAVE2 projects?
What is the impact of gypsum on phosphorus leaching?
Does gypsum influence crops?
Does gypsum amendment affect a plant’s ability to absorb phosphorus or other nutrients from the soil?
Does gypsum alter the soil’s pH?
Does gypsum contain sulphur?
What must be taken into account at farm level?
What types of fields are suitable for gypsum treatment?
What types of soil can benefit from gypsum as a method of water protection?
Does gypsum affect soil microbiota?
Can gypsum be used in the catchment areas of lakes? How about in groundwater areas?
Does the use of gypsum affect aquatic biota?
How long does the effect of gypsum last?
What is gypsum and where does it come from?
How is the gypsum transported to the farms?
What kind of equipment can be used to apply the gypsum?
What is the most optimal time of year for spreading gypsum? How should the spreading be timed in relation to other field work?
Could gypsum application prevent other measures planned for the farm?
Could gypsum become a compulsory additive for farmers in the future?
Will the application of gypsum impact EU subsidies?
What are the costs of gypsum treatment? How about cost-effectiveness of gypsum?
Why is there so much research into gypsum treatment?

What are the SAVE and SAVE2 projects?

The SAVE project (2016–2018) was a joint research project between the University of Helsinki and the Finnish Environment Institute. The goal of the project was to examine how gypsum amendmentof fields would work as a water protection method in large scale. A gypsum-spreading pilot was carried out in the Savijoki river basin in collaboration with local farmers. The SAVE project examined farmers’ experiences and the impact of gypsum on water bodies and the nutritional state of the soil and crops. The SAVE project’s research in the pilot area is now continuing in the SAVE2 project.

The SAVE project was funded by the Ministry of the Environment (2016–2018) and was part of the government’s circular economy key project. The Ministry of the Environment is also funding the SAVE2 project (2019–2020). The gypsum pilot in the Savijoki river basin was implemented in collaboration with the NutriTrade project (2015–2018), funded by the EU Interreg Central Baltic programme.

Based on the research on gypsum amendment and the experiences gathered during the SAVE project, an information package Gypsum amendment of fields as a water protection method in agriculture was compiled, and national policy recommendations were drafted for the large-scale implementation of gypsum and its inclusion in the agricultural support scheme. Under the NutriTrade project, international policy recommendations (NutriTrade Policy Brief 1 and NutriTrade Policy Brief 2) were published for promoting the use of gypsum in the protection of the Baltic Sea.

What is the impact of gypsum on phosphorus leaching?

Gypsum reduces the amount of phosphorus making its way to waterways from agricultural fields, both in runoff and bound in soil. Both the calcium and the sulphate contained in gypsum increase the ionic strength of the soil, meaning that the soil particles form larger aggregates which cannot be carried to the waterways as easily with rainwater or melting snow. The calcium contained in gypsum is particularly effective at increasing the aggregate size in soil. Gypsum also facilitates the binding of phosphorus in the soil particles in a way that maintains the phosphorus available for plants. In addition, gypsum reduces the leaching of organic carbon. These effects begin as soon as the gypsum has dissolved into the soil and last an estimated 4–5 years.

Does gypsum influence crops?

Gypsum does not decrease crop yield, and may in some situations even increase it. For example, certain crucifers may benefit from the sulphate sulphur in the gypsum. With the gypsum, approximately 8kg/ha of phosphorus is introduced into the soil as “impurities”, which is a small amount considering that the gypsum is not applied annually. On the other hand, the sulphate may temporarily reduce plants’ ability to absorb selenium for the first year after application. This potential reduction in the amount of selenium must be considered if the crop is to be used as animal feed during the year following gypsum application.

Does gypsum amendment affect a plant’s ability to absorb phosphorus or other nutrients from the soil?

Gypsum amendment does not affect a plant’s ability to absorb phosphorus or other nutrients, with the exception of selenium. Gypsum amendmentfacilitates the natural binding of phosphorus to the surface of soil particles. However phosphorus remains available to plants.

The sulphate contained in gypsum can affect a plant’s ability to absorb selenium. However, this effect only applies to the first harvest, when the soil’s sulphate level is at its highest. Farmers can prepare for this either by using selenium-rich fertilizers or by adding selenium to animal feed. Usually, the selenium reserves in soil are very low. During the SAVE project monitoring, the selenium levels in the research area were so low to begin with that the short-term decrease in selenium levels observed in the TraP project could not be verified.

In studies carried out in Finland, gypsum treatment has not been found to affect the absorption of other nutrients, apart from selenium. Thus far, gypsum has not been observed to affect a plant’s absorption of magnesium or potassium. The subject will be further explored in the SAVE2 project.

Does gypsum alter the soil’s pH?

Gypsum does not alter the soil’s pH. As gypsum contains calcium, some people may perceive it as a liming material that increases the soil’s pH. On the other hand, the sulphur contained in gypsum could be perceived as lowering the soil’s pH. However, the pH of a field does not change one way or the other because gypsum is a neutral salt, i.e. its calcium and sulphate ions cannot alter the pH. If the pH of a field needs to be increased, appropriate liming materials should be used.

Does gypsum contain sulphur?

Approximately 18% of the gypsum is sulphur. This means that for every 4,000kg of gypsum per hectare, 720kg of sulphur will be introduced into the soil per hectare. Gypsum application may help with sulphur deficiency. The sulphur included in the gypsum must be accounted for, if sulphuric fertilisers are being planned.

What must be taken into account at farm level?

According to the EU organic farming regulation, natural gypsum can be used in organic farming but industrially produced gypsum (such as Siilinjärvi gypsum) cannot.

Gypsum is not recommended for use in fields that have a deficiency of potassium or magnesium and are correspondingly rich in calcium. The addition of calcium displaces potassium and magnesium from the surfaces of soil particles, highlighting the imbalance between their various cations. Gypsum does not affect the acidity of arable land. If there is an acidity problem in a field, it is recommended to be treated with lime before using gypsum as a means of water protection. If a well is located in the gypsum spreading area, a protected zone should be left around the well.

Gypsum produced as a by-product of the phosphoric acid industry contains a small amount of phosphorus (e.g. 0.2% in Siilinjärvi gypsum). The farmer may choose to take this into account when determining the amount of phosphorus fertilisation. However, the fertiliser restrictions associated with environmental compensation take no account of the amount of phosphorus contained in gypsum.

What types of fields are suitable for gypsum treatment?

Gypsum can be used on crop fields which are ploughed or cultivated after harvesting, or on no-till fields used for spring grain.

Gypsum can be applied on grassland, if the field is reformed and cultivated at the time of application. As the suitability of gypsum for grassland has not been sufficiently tested, grassland fields were excluded from this project due to its breadth. In the project, the gypsum is used primarily to protect waterways, so the fields that are of primary interest are ones with a large risk of nutrient leaching.

According to the EU organic farming regulation, natural gypsum can be used in organic farming but industrially produced gypsum (such as Siilinjärvi gypsum) cannot.

As gypsum contains calcium, each field plot should be inspected to ensure it is suitable for gypsum application. For example, no gypsum should be used on over-limed fields.

Nor should gypsum be applied on no-till plots of autumn grain. If the gypsum does not fully dissolve into the soil, the sodium content of topsoil may temporarily reach levels which are detrimental to the growth of the new crop. The time needed for the dissolution of the gypsum depends on the amount of rainfall after application.

What types of soil can benefit from gypsum as a method of water protection?

Gypsum has proven effective in reducing phosphorus leaching, especially in clay soils, where it has been studied the most. Thus, gypsum works well, at least in clay soils. In clay soils, the soil particles are small and easily run off with water. The efficiency of gypsum in clay soils is supported by the theory of the aggregation of small soil particles.

Both in Nurmijärvi and Savijoki, gypsum has also been spread on mineral soils, which are coarser than clay. Mineral soils accounted for one fifth of the Savijoki river pilot area. Gypsum may also work on these types of soils too. However, little research exists on the effectiveness of gypsum in soils other than clay. Thus, this subject should be studied further. Gypsum should not be used in acidic sulphate soils as this would not significantly benefit water bodies because phosphorus leaching is already minimal.

Does gypsum affect soil microbiota?

There is little research-based data on the effects of gypsum on soil microbiota. The biological health of soil is an important factor for productivity and the environment. However, only minimal research has been conducted on the subject and the effects of most agri-environmental measures on soil microbiota and microbiology remain largely unknown.

The increase in conductivity and sulphur content caused by gypsum treatment has been considered harmful to soil microbiota. These kinds of impacts are generally difficult to study as the subject is very broad and multi-dimensional. For example, only a part of microbes and their functions are known. Presumably, different microbes and other organisms thrive in different kinds of conditions and react to changes in different ways.

In the SAVE project, we have consulted experts and, in 2017, we analysed the microbial activity in soil samples taken in the pilot area. No differences were detected between the treated and untreated plots. However, microbial activity is only one of the many research-worthy topics within the subject area. In collaboration with experts, the SAVE2 project will explore in greater detail how best to approach the subject.

Can gypsum be used in the catchment areas of lakes? How about in groundwater areas?

In lake-basin areas gypsum should not be used until information can be gained on how strongly sulfate runoff affects the sulphur content of bottom waters especially in lakes with slow water exchange. A rise in sulfate levels could increase the release of phosphorus from lakebed sediments and accelerate eutrophication. In addition, gypsum is not recommended for use in or near Natura areas.

In the monitoring of the SAVE project, gypsum has not been detected in groundwater. In groundwater areas, careful consideration should be given to the use of gypsum, as for other agricultural activities such as the spreading of slurry.

Does the use of gypsum affect aquatic biota?

As gypsum is freely soluble, it is easily leached by run-off waters. Calcium is not harmful to the aquatic environment, but in high quantities, sulphate can harm aquatic organisms. Thus, the sulphate contained in gypsum and its effects on the ecology of flowing waters has been considered a risk factor of gypsum treatment. In the SAVE project, the sulphate levels of run-off waters after the spreading of gypsum remained moderate and any higher levels were short term. The sulphate leached by run-off waters was not found to be harmful to the biota of flowing waters. The species studied were: greater water moss (Fontinalis antipyretica), thick-shelled river mussel (Unio crassus) and trout (Salmo trutta).

How long does the effect of gypsum last?

The effect of gypsum lasts approximately five years. There are differing views on the duration of the effect of gypsum due to the different results produced by different studies. In the rain simulation tests carried out by Uusitalo et al (2012), in which field samples were studied in laboratory conditions the effect of gypsum waned during the third year. The TraP research project carried out in Nurmijärvi, in which gypsum was spread over an area of at least 100 hectares, was the first experiment in which laboratory results were exposed to the random fluctuation of circumstances and weather conditions at river basin level. The effect of gypsum over time was examined by monitoring the quality of river water and soil. The effect of gypsum could be detected in river water for the duration of the five-year monitoring, after which the project, and therefore also the monitoring, unfortunately ended. Over the last year and a half, the effect showed some signs of waning, but during the last spring of monitoring, the effect was at the same level as right after the gypsum had been spread. We also monitored the quality of water in the Nurmijärvi pilot area in 2017. However, in these results, the effect of gypsum showed no clear signs of either enduring or waning.

Under the SAVE project, the effect of gypsum has now been monitored in both water and soil for a little over two years, and the SAVE2 project will enable the monitoring of these effects until the end of 2020. It is our ardent desire that the monitoring can continue for as long as we can truly prove that the effect of gypsum has waned. The Vantaanjoki gypsum project also includes continuous monitoring at river basin level, and this will probably continue for a long time.

Determining the magnitude and duration of the effects of gypsum amendment is important in order to draft more detailed guidelines on questions such as: When is it safe to repeat gypsum amendment , and when is the best time to do it from a water protection point of view?

What is gypsum and where does it come from?

The gypsum used in the SAVE project comes from the YARA factory in Siilinjärvi, where it is a byproduct of fertiliser production. When apatite minerals (or apatite stone) are treated with sulphuric acid, phosphoric acid and gypsum (calcium sulphate hydrate, CaSO4 ∙ 2H2O) are produced. The apatite mined in Siilinjärvi contains no heavy metals or radioactive substances. This means that the calcium sulphate, i.e., gypsum, produced there is also free from dangerous substances and suitable for agricultural use.

The Siilinjärvi gypsum contains approximately 15% water, and has a specific gravity of 1,500kg/m3. The gypsum contains 23% calcium and 18% sulphur as well as no more than 0.2% phosphorus and approximately 0.2% fluoride as impurities derived from the fluoride apatite used as a raw material.

How is the gypsum transported to the farms?

The gypsum was transported to the farms directly from Siilinjärvi in trucks. The initial plan was to use trains for transportation. This proved to be more expensive than trucks, and would have required more loads as well as the construction of an interim storage facility. The amount of gypsum used in the project was large, but not large enough to make rail transport a cost-effective option. If the use of gypsum is adopted more widely in the future, the transportation of gypsum by rail to interim storage may prove to be a better option.

What kind of equipment can be used to apply the gypsum?

In practice, the gypsum is applied in a similar manner as agricultural lime, just at a different time of the year. The gypsum comes in a powder, like lime. Gypsum is spread evenly on the farm plots, 4,000kg per hectare. A wet lime spreader or a broadcast spreader intended for dry fertiliser can be used. Gypsum spreading equipment was tested in the TTS Work Efficiency Institute study in autumn 2008.

What is the most optimal time of year for spreading gypsum? How should the spreading be timed in relation to other field work?

The most favourable time of year for spreading gypsum is in the autumn after the harvest and before any tilling. The timing should be as close to tilling (ploughing or light tilling) as possible so that the gypsum dissolves and mixes faster with the soil. Spreading can also take place in the spring if the tilling is carried out after the spreading. Gypsum can also be used in no-tillage fields if the spreading takes place in the autumn and the sowing is in the spring. At the earliest, gypsum can be spread right after harvesting. In order to prevent soil compaction, gypsum should be spread during  dry periods. In the SAVE2 project, the practical questions related to the spreading of gypsum and its effects will be further explored – especially the winter spreading of gypsum via a snow spreading test conducted in a laboratory

Could gypsum application prevent other measures planned for the farm?

The application of gypsum results in no restrictions on other farm work.

It is recommended to plough or cultivate the soil after the application of the gypsum. This means that the gypsum will dissolve and mix into the soil faster. However, gypsum can also be applied on no-till fields, if the gypsum is spread in the autumn and sowing takes place in the spring.

Gypsum does not alter a field’s pH. If the pH of a field needs to be increased, appropriate liming materials should be used. If there are plans to spread both gypsum and lime on the same plot, the total amount of calcium in both substances should be taken into account.

Could gypsum become a compulsory additive for farmers in the future?

It is possible that the application of gypsum will become a part of the agri-environmental support system. It is highly unlikely that gypsum will become a compulsory additive financed by the farmers. One reason for this is that gypsum cannot be used on all fields.

Will the application of gypsum impact EU subsidies?

No. Even though the gypsum contains at most 0.2% phosphorus, this is not considered in the agri-environmental support system, as chemical compounds spread on the fields for phosphorus retention are excluded (Decree of the Ministry of Agriculture and Forestry regarding environmental support, 375/2015, section 3, Phosphorus fertilisers).

What are the costs of gypsum treatment? How about cost-effectiveness of gypsum?

Because gypsum amendment does not reduce yields or the arable area, it does not result in loss of income for farmers. In addition, no equipment investments are required, since gypsum can be spread using existing equipment. The costs of gypsum amendment have been ascertained in the Savijoki river pilot and earlier projects, all of which involved the use of Siilinjärvi gypsum. The total cost of the process was around EUR 220 per hectare. Transportation from Siilinjärvi to the farms accounted for about 60% of the cost. The remainder is divided between the material and the costs incurred at the farm.

The cost of gypsum amendment in proportion to its ability to reduce the phosphorus load in agriculture is around EUR 60 to 70 per kilogram of phosphorus reduced. Such a benchmark can help in finding the most advantageous ways of reducing the phosphorus load in agriculture. Existing means of reducing the phosphorus load, such as the addition of protection strips and wetlands, would be considerably more expensive.

Why is there so much research into gypsum treatment?

Good results have been attained on the use of gypsum to reduce phosphorus pollution from agriculture in both previous studies and smaller-scale trials. In addition, this approach is estimated to be both more cost-effective and act faster than any other method of waterway protection currently in use.

However, there were several questions and challenges relating to the widespread adoption of gypsum, of which more information was necessary before it could be recommended for broader use. A large-scale gypsum-spreading pilot was carried out under the SAVE project to gain information on its usability on extensive catchment areas. The use of gypsum has never before been studied on such a large scale.

The extensive pilot of the SAVE project was intended to glean more information on practicalities, such as the availability of the gypsum and related logistics, the spreading of gypsum and how gypsum application would fit in with other agricultural work. In addition, further information was being sought on the impact of gypsum on the soil and on crop yield.

Based on the research on gypsum amendment and the experiences gathered during the SAVE project, an information package Gypsum amendment of fields as a water protection method in agriculture was compiled. The SAVE project’s research in the pilot area is now continuing in the SAVE2 project.