Calcium sulfate

Toxicity to terrestrial plants

Description of key information

Calcium sulfate is not expected to have a detrimental effects on terrestrial plants due to its natural occurence in the environment.

Additional information

Calcium sulfate, calcium and sulfate ions are ubiquitous in the environment. Calcium is an important constituent of most soils and the minerals found in soil are mostly compounds of calcium with other substances. Furthermore, calcium sulfate, as Gypsum, is used as an inorganic fertiliser to improve soil quality. Important applications include:

• for the reclamation of sodic soils through ion exchange (calcium replacing sodium)

• to reduce run-off water and its resulting erosion in dry agricultural areas as an ameliorant for acidic subsoils and soils in forestry

• to improve Ca- and S-nutritional elements in agriculture (rape and cereals)

• Gypsum is also useful as an additive for soils with high levels of sodium

The European Committee Joint Research centre have summarized a number of papers as part of an assessment of the effect of gypsum on plants. Van Alphen and de los Rios Romero (1971) conclude that up to 2 percent gypsum in the soil favours plant growth, between 2 and 25 percent has little or no adverse effect if in powdery form, but more than 25 percent can cause substantial reduction in yields. They suggest that reductions are due in part to imbalanced ion ratios, particularly K:Ca and Mg:Ca ratios. Hernando et al. (1963, 1965) studied the effect of gypsum on the growth of corn and wheat by varying the gypsum level in the soil up to 75 percent. They show that high levels of gypsum caused poor growth of corn, especially as the soil moisture was maintained at 80 percent of field capacity. However, wheat showed minimum growth where the soil contained 25 percent gypsum at all soil moisture levels ranging from 15 to 100 percent of field capacity. Akhvlediani (1962) concludes in general, that agricultural production on gypsiferous soils is not affected when the gypsum content is between 15 and 30 percent.

The various reports quoted by JRC suggest that the effect of gypsum on plants is extremely variable depending on the plant, soil type and location. However, the overall results indicate that apart from special crops (e.g. certain fruit trees) the gypsum concentration in soils should be limited to 15 %.

Investigations by Sanderson (2004), on behalf of Agriculture & Agri-Food Canada, on the use of gypsum as an organic amendment in lowbush blueberry production, indicated that gypsum application, with or without fertiliser application, was an effective method to increase nutrient uptake in the lowbush blueberry. Gypsum significantly influenced nutrient uptake and general plant health more than any other fertiliser application evaluated in this region.

Sulfur (as sulfate) is a major plant nutrient, and is essential for crop growth.

Calcium is an important constituent of most soils and the minerals found in soil are mostly compounds of calcium with other substances. Soil calcium is necessary for proper plant functions and helps in producing healthy fruits and flowers.

Some of the functions that require soil calcium include enzyme activity for the absorption of other nutrients, proper cell formation and division, increased metabolic activities, starch breakdown and nitrate uptake. Without soil calcium plants tend to lose their colour, have a short life and produce little or no fruit.

Many fertilisers available today make use of calcium and calcium-rich salts to neutralise soils and make them less acidic. Calcium has strong relationships with other substances found in the soil like magnesium, potassium and sodium. Together these nutrients make the soil so rich that almost all kinds of plants can be grown with it.

Soil calcium is mainly important for lowering the pH level and the associated acidity. It is often recommended to include up to 40 – 50% of calcium in any fertilizer to account for its deficiency in the soil. The resulting plants will have stronger roots and better growth rate than a calcium deficient soil. In addition to this, calcium also helps in regulating the flow of water and air in the soil for proper absorption by the plant cells.

Calcium is known as an essential nutrient for higher plants and one of the basic inorganic elements of algae. Calcium plays crucial roles in strengthening cell walls and plant tissues, reducing the toxicity of soluble organic acids, elongating roots, and so on.

The calcium content of plants varies between 0.1 and > 0.5% of the dry weight depending on the growing conditions, plant species, and plant organ. In well-balanced growing nutrient solutions with controlled pH, maximal growth rates were obtained at calcium supply levels of 2.5-100 uM. Also, calcium can be supplied at higher concentrations and might reach more than 10% of the dry weight without symptoms of serious inhibition of plant growth, at least in calcicole plant species.

Typical symptoms of calcium deficiency are the disintegration of cell walls and the collapse of the affected tissues, such as the petioles and upper parts of the stems. Lower calcium contents in fleshy fruits also increase the losses caused by enhanced senescence of the tissue and by fungal infections.

Given the extensive and continued use of calcium sulfate as a fertiliser and for chemical treatments of soils and its natural occurrence in the environment, it is considered that calcium sulfate would not have a detrimental effect on plants at the concentrations released to soil. Therefore, the performance of a short-term toxicity test to plants is not scientifically justified.

References:

Van Alphen and De Los Rios Romero F (1971) Gypsiferous soils, notes on characteristics and management. Int Inst of Land Recl and Improv. Bulletin 12. Wageningen. The Netherlands

Hernando V., Sanchez Conde. MP and Contreras JG (1965) Study of the mineral nutrition of maize on soils rich in gypsum Zolfo in Agricoltura Palermo 1964; 398-411

Sanderson K (2004), Gypsum as an Organic Amendment in Lowbush Blueberry Production, Agriculture & Agri-food Canada, Report 2004F-05E

Nachtergaele F, FAO, Rome – Italy, Criterion 6.3 “Soil gypsum content” cited in Common bio-physical criteria to define natural constraints for agriculture in Europe, JRC Scientific and Technical Reports, Draft report EUR XXXXX EN.