Chemical compatibility of fertilizers refers to the ability of two or more fertilizers to be mixed without adverse effects. These reactions could decrease the solubility of nutrients, cause precipitation of insoluble salts or produce compounds that negatively impact plant development.
Understanding how the different nutrients interact and the chemical compatibility of fertilizers is a key aspect to guarantee proper nutrition in crops, optimizing their use and minimizing solubility and phytotoxicity issues.
There are several factors and considerations that must be considered to determine whether fertilizers can be mixed safely and efficiently. The most important are:
- Optimizing the solution pH: An inadequate pH can alter the chemical form of some nutrients, decreasing their solubility and availability for the plant. An illustration of this is phosphorus, which tends to precipitate at high pH, forming insoluble compounds with calcium and magnesium. Adjusting the pH of the solution to 5.5-6.5 promotes the solubility of most nutrients and decreases the potential of insoluble compounds formation.
- Combination of nutrients: Some nutrients, such as calcium and phosphate, are especially prone to form precipitates when mixed in concentrated solutions. In fertigation systems, using separate mixing tanks for incompatible nutrients reduces the potential blockages in the system and ensures that each nutrient reaches the roots optimally.
- Adapting the concentration of fertilizers: Mixtures with high concentrations of fertilizers can increase the potential precipitation and blockage in irrigation systems. Diluting solutions properly before mixing helps to avoid these adverse effects.
- Knowing the temperature and quality of the water: Hard water (high in calcium and magnesium) increases the potential precipitation of insoluble salts when mixed with phosphates or sulphates. In addition, low temperatures often decrease the solubility of some compounds, which may increase incompatibility in cold solutions.
- Conducting compatibility pre-tests: When combining fertilizers for the first time, it is recommended to conduct a compatibility test in a small volume of water. This allows to observe potential precipitates or adverse effects before applying on a large scale.
TABLE 1.- COMPATIBILITY OF THE MAIN TYPES OF FERTILIZERS
Understanding how nutrients interact, adjusting the pH of mixtures and using appropriate application practices help to maximize nutrient availability for plants, minimizing application issues and reducing the risk of phytotoxicity. A knowledge-based approach and careful management of chemical compatibility improves not only agronomic efficiency, but also the logistics and economics of application.
