Salt Effect occurs when the concentrated fertilizer is located too close to the seed or seedling, causing desiccation. The effects of desiccation will vary depending on:

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.

In this example, the fertilizer is in the initial stages of nitrification, forming the ammonia retention zone (red). One seed has fallen into the band of fertilizer, and is suffering the full effects of salt effect. One seed is on the seed shelf on the edge of the retention zone, and stands a greater chance of surviving.

The seed is out of harms way while the nitrogen is in a very concentrated form (red). A small amount of nitrate (NO3) (green) has formed, and begins moving away from the core of the concentrated band. The seed has begun to germinate utilizing the available nitrogen in the soil, the seed, and the starter fertilizer.

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

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.