Phosphate rock is acidified with nitric acid to form a mixture of phosphoric acid and calcium nitrate during the nitrophosphate fertilizer manufacturing process. Ammonia is then added to neutralize excess acidity. Calcium nitrate crystals precipitate via a temperature gradient and are separated as the mixture is cooled. With the ammonia addition and crystallization, a double salt is formed [5 Ca(NO3)2•NH4NO3•10 H2O, referred to as 5:1:10 double salt] and is considered the commercial grade of calcium nitrate. Hence, small amounts of ammonical N may also be present in this grade of calcium nitrate.
Calcium nitrate is very hygroscopic (absorbs water from the air), so when intended for soil application, proprietary coatings are applied to minimize moisture uptake. Calcium nitrate intended for hydroponics or fertigation does not contain a conditioner, or it may be sold as a clear fluid fertilizer ready for use.
Calcium nitrate is popular in agronomic situations where a readily soluble source of nitrate or calcium is needed. Nitrate moves freely with soil moisture and can be immediately taken up by plant roots. Unlike many other common N fertilizers, Ca(NO3)2 application does not acidify soils since there is no acidity producing nitrification of ammonium occurring. Broadcast applications of Ca(NO3)2 are desirable in some circumstances because the risk of ammonia volatilization is eliminated with its use. In addition, some crops prefer nitrate sources of N.
Applications of Ca(NO3)2 are also used to provide supplemental Ca for plant nutrition. Some soils may contain considerable amounts of Ca, but it may not be sufficiently soluble to meet plant demands. Since Ca is not mobile in the plant it is important to apply Ca just-in-time in critical growth stages. Solutions of Ca(NO3)2 are commonly added to irrigation water and to foliar and fruit sprays to overcome such shortcomings that can affect yield and/or quality (such as apple bitter pit), or to meet peak Ca demands during critical growth periods. Part of the popularity of Ca(NO3)2 also arises from its chloride-free nature and Ca(NO3)2 can have an ameliorating effect under saline growing conditions, combating the negative effects of Na and Cl-.
Research has shown that a healthy plant with adequate Ca alleviates biotic and abiotic stresses such as fungal disease, and stresses due to drought, heat, or cold. Hence Ca(NO3)2 is widely used in intensive cropping systems that have a high focus on crop quality.
There are no special practices required for the use of Ca(NO3)2 beyond the need to keep nitrate from moving below the root zone.
To avoid precipitating insoluble fertilizer salts, Ca(NO3)2 should not be mixed with soluble phosphate or sulfate fertilizers in nutrient solutions or while fertigating. The extreme hygroscopic nature of solid Ca(NO3)2 makes it important to store it in a cool and dry environment.
Calcium nitrate (double salt) is not classified as an oxidizer by government agencies, so there are no special restrictions on transport and handling as there may be for ammonium nitrate. However calcium nitrate tetrahydrate is classified as a 5.1 oxidizing agent that can, in conjunction with oxygen, cause or increase the combustion of other materials and may require special attention depending on local regulations.
Calcium nitrate is used for waste water treatment to minimize the production of hydrogen sulfide. It is also added to concrete to accelerate setting and reduce corrosion of concrete reinforcements.
This acticle is from a IPNI Nutrient Source Specific article on fertilizer materials available here: