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¶ Introduction
Potassium nitrate (KNO3) is a soluble fertilizer commonly used for high-value crops that benefit from nitrate (NO3) nutrition and a source of potassium (K+) free of chloride (Cl-). This compound is traditionally known as “saltpeter”.
¶ Production
Potassium nitrate fertilizer is sometimes referred to as “nitrate of potash (NOP)”. It accounts for only a small portion of the global potassium fertilizer market.
NOP is typically made by reacting potassium chloride (KCl) with a nitrate source. Depending on the objectives and available resources, the nitrate may come from sodium nitrate, nitric acid, or ammonium nitrate. The resulting potassium nitrate is identical regardless of the manufacturing process.
Potassium nitrate is commonly sold as a water-soluble, crystalline material primarily intended to dissolve for application with water or in a prilled form for soil application.
¶ Table 1. |
|
| Property | K2NO3 |
| Fertilizer analysis | 44% to 46% K2O |
| 13% to 13.5% nitrogen | |
| Water solubility @ 68°F | 316 g/L |
| Solution pH | 7 to 10 |
¶ Agricultural Use
The use of potassium nitrate is especially desirable in conditions where a highly soluble, chloride-free nutrient source is needed. All of the nitrogen is immediately available for plant uptake as nitrate, requiring no additional microbial action or soil transformation.
Growers of high value vegetable and orchard crops sometime prefer to use a nitrate-based source of nutrition in an effort to boost yield and quality. Potassium nitrate contains a relatively high proportion of potassium, with a nitrogen-to-potassium ratio of approximately 1:3. Many crops have high potassium demands and can remove as much or more potassium than nitrogen at harvest.
Potassium nitrate applications to the soil are made before the growing season or as a supplement during the growing season. A diluted solution is sometimes sprayed on plant foliage to stimulate physiological processes or to overcome nutrient deficiencies.
Foliar application of potassium during fruit development can be advantageous for some crops, since this growth stage often coincides with high potassium demands during the time of declining root activity and nutrient uptake. It is also commonly used for greenhouse plant production and hydroponic culture.
¶ Figure 1. Water Solubility of Common K Fertilizers
¶ Figure 2. KNO3 Crystals and Prills
¶ Management Practices
Potassium nitrate is often applied to soil or through the irrigation system during the growing season to support harvest quality, protein formation, disease resistance, and water use efficiency
This fertilizer is primarily used where its unique composition and properties provide specific benefits to growers. It is easy to handle and apply, and is compatible with many other fertilizers. This includes usage for many high-value specialty crops, as well as grain and fiber crops.
The relatively high solubility of potassium nitrate under warm conditions allows for a more concentrated solution than for other common potassium fertilizers. Careful water management is needed to keep the nitrate from moving below the root zone.
¶ Non-agricultural Use
Potassium nitrate has long been used for fireworks and gunpowder. It is now more commonly used in food to maintain the quality of meat and cheese. Specialty toothpastes often contain potassium nitrate to alleviate tooth sensitivity. A mixture of potassium nitrate and sodium nitrate (NaNO3) is used for storing heat in solar energy installations.
¶ References
IPNI. Nutrient Source Specifics No. 11: Potassium Nitrate. International Plant Nutrition Institute, Norcross Georgia. 1 pg.