Although calcium cyanamide fertilizer is harmful to health, it is still used. We explain what disadvantages the fertilizer has and show alternatives. Calcium cyanamide combines the fertilization of nitrogen with the liming of the soil and broad control of harmful organisms. However, as we will show you, what at first sight seems to make sense and is advertised as such by distributors of the fertilizer primeval rock also entails some significant disadvantages.
What is calcium cyanamide fertilizer?
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The chemical name of calcium cyanamide is calcium cyanamide (CaNCN or CaCN2). The dirty gray-black powder or granules have been produced for over 100 years by binding atmospheric nitrogen to calcium carbide at high temperatures and with high energy consumption.
19.8% of the substance is nitrogen, 60% is calcium oxide, and the rest is carbon and often impurities such as iron and aluminum. Because calcium cyanamide contributes not only nitrogen but also lime, and also has a herbicidal, bactericidal, and fungicidal effect, it can be called a multifunctional nitrogen fertilizer.
How does calcium cyanamide fertilizer work?
Calcium cyanamide is activated in the soil when it comes into contact with liquid water. The reaction takes place even at cool temperatures. Below we distinguish three different effects of calcium cyanamide fertilizer.
Calcium hydroxide (slaked lime) is formed, which is easily soluble and can quickly raise the pH of the soil or be absorbed by plants. One-third of the lime contained is present in slower-acting lime forms.
Liming the upper soil layer improves the soil structure, provides stable crumbs, better aeration and water absorption of the soil, and also stimulates soil respiration. The pH value of the soil is raised. The lime effect is equivalent to 60% CaO, so calcium cyanamide can be treated in liming like lime with 60 grams of calcium oxide in 100 grams.
After dissolution, the nitrogen is present as cyanamide (H2CN2). This is converted after a few days to urea and – to a lesser extent – dicyandiamide (DCD). While the area soon becomes plant-available ammonium and nitrate, DCD is present in the soil for longer without being converted. Thus, a long-term effect is achieved and the fertilized nitrogen is less prone to leaching.
Cyanamide is effective in the upper three to four centimeters of soil against many weeds and their seeds, slugs, wireworms, and numerous soil-borne fungi, such as plasmodia, which are unicellular parasites of cabbage hernia (Plasmodiophora brassicae). This effect is temporary, however, as the cyanamide continues to be converted.
Disadvantages of calcium cyanamide fertilizers
In 2016, an opinion from the EU health authority found that calcium cyanamide can harm human health and contaminate surface and groundwater. This is true, it said, with both the manufacturers’ recommended and improved application methods.
In addition, ingestion of cyanamide – for example as dust – can lead to so-called calcium cyanamide disease: Cyanamide inhibits acetaldehyde dehydrogenase, which is responsible for the breakdown of acetaldehyde in the blood. Acetaldehyde is a degradation product of ethanol (drinking alcohol) and leads to dizziness, nausea, and flushing.
Thus, if alcohol is consumed after ingesting cyanamide, even small amounts will cause one to experience an incredibly bad, long-lasting hangover as the acetaldehyde accumulates in the blood. However, when used properly – especially by wearing a mouthguard – a large enough ingestion of cyanamide is prevented. Because calcium cyanamide fertilizer is corrosive, it is essential to wear gloves when applying it.
The versatile nitrogen fertilizer also has other disadvantages: it has a strong humus-depleting effect because it rapidly stimulates bacterial soil life for a few weeks by increasing the pH value. These organisms consume large amounts of carbon to produce energy. However, because calcium cyanamide does not provide organic, carbon-rich material as a substrate, the bacteria feast on the soil’s own carbon, or humus.
At the same time, fungi, also extremely important soil builders, are damaged by the sudden rise in pH. Since various fungi are in symbiosis with our plants, this cannot be beneficial to us. And of course, this effect is compounded by the biocidal effect of cyanamide: This naturally does not distinguish between harmful and beneficial bacteria, fungi, and plants – like a chemical club, it strikes a wide swath into soil life.
Alternatives to calcium cyanamide fertilizers
The nitrogen requirements of soils are met in a much more resource-conserving, natural, and soil-compatible way with the help of primarily organic fertilizers. Should you nevertheless absolutely want to use calcium cyanamide – for example, to avoid having to dispose of old stocks – we strongly recommend that you first determine the pH value of your soil so as not to drive it to plant-intolerant heights.
The parallel incorporation of stable organic material such as straw, bark humus, or bark mulch helps to protect the humus in the soil. An alternative to the broad biocidal action of calcium cyanamide is the targeted control and, in some cases, the benevolent tolerance of organisms that do not necessarily provide us with a direct benefit in the home garden, but which invariably fulfill an ecological benefit.