Mixing Fertilizers
The best policy is to not mix fertilizers. However, if mixing is necessary for microirrigation, follow the considerations below. These considerations are based on information contained in a UNOCAL compatibility chart. More detailed information about other reactions can be found in the compatibility chart.
Chemical storage for a microirrigation injection system. Photo: L. Schwankl
- Ammonium nitrate (AN-20). Incompatible fertilizers include ammonium polyphosphate, aqua-sulfur, calcium ammonium nitrate solution (CAN-17), calcium nitrate, diammonium phosphate, monoammonium phosphate, and urea-sulfuric acid. With certain limits, AN-20 is compatible with phosphoric acid, sulfuric acid, and potassium chloride.
- Calcium nitrate. Incompatible fertilizers include ammonium nitrate (AN-20), ammonium phosphate solution, ammonium polyphosphate solution, ammonium polysulfide solution, ammonium sulfate solution, ammonium thiosulfide solution, diammonium phosphate, monoammonium phosphate, urea-sulfuric acid, phosphoric acid, potassium chloride, sulfuric acid, and urea ammonium nitrate solution (UAN-32).
- Calcium ammonium nitrate (17-0-0-8.8 Ca). Incompatible fertilizers include ammonium nitrate (AN-20), ammonium phosphate solution, ammonium polyphosphate solution, ammonium polysulfide solution, ammonium thiosulfide solution, ammonium sulfate solution, diammonium phosphate, monoammonium phosphate, urea-sulfuric acid, phosphoric acid, potassium chloride, sulfuric acid, and urea ammonium nitrate solution (UAN-32).
- Urea-ammonium nitrate solution (UAN-32). Incompatible fertilizers include ammonium nitrate (34-0-0), calcium nitrate, diammonium phosphate, monoammonium phosphate, urea-sulfuric acid, nitric acid, phosphoric acid, potassium chloride, and sulfuric acid. With certain precautions, UAN-32 is compatible with ammonium phosphate, ammonium polysulfide, and aqua-sulfur solution.
For additional information on prevention and mitigation of clogging caused by fertilizer interactions, click here.