Agronomy Ag Fundamentals

Salt Effect

The Effects of Desiccation

• amount of moisture present in the soil;
• type of fertilizer being applied;
• rate of fertilizer application;
• proximity of the fertilizer to the seed.

Salt Index Rating

All granular and liquid fertilizers have a Salt Index Rating, indicating the relative strength of the salt in the fertilizer. Salt content is one of the most critical characteristics of fertilizers. The Salt Index (SI) of a fertilizer is a measure of the salt concentration that fertilizer induces in the soil solution relative to Sodium Nitrate. Sodium nitrate was chosen as the standard because it was 100 percent water soluble and it was a commonly used nitrogen fertilizer when the SI concept was first proposed in 1943.

Salt Effect of Common Fertilizers

The higher the rating, the greater the salt effect can be to the plant.

• Urea (46-0-0) and Liquid UAN (28-0-0) are relatively close in salt index rating. The same care should be taken with the application of Liquid UAN as with granular urea, especially if seeding in dry, highly fractured or sandy soil.
• Anhydrous ammonia has a lower salt index rating, but still must be applied with care due to the large pH changes and affinity to water while converting to a plant available form of nitrogen
• The low salt index for phosphate (12-51-0) explains part of the reason why phosphate can be placed safely with most seeds. Recommended rates must still be followed when seed-placing phosphate.

Minimize Risk of Salt Effect

Placing the nitrogen fertilizer at a safe distance from the seed row will protect the seed from the desiccation effect. Fertilizers such as Urea or Liquid UAN have a relatively high salt index rating, and must we applied with more caution. Fertilizers with lower salt index ratings, such as monoammonium phosphate can be used in a seed-placed application, but recommended rates must still be followed.