Salt Effect
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:
  • 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 Index Ratings
Table Salt (Sodium Chloride)
153
Ammonium Nitrate (34-0-0)
104
Sodium Nitrate (NaNO3)
100
Urea (46-0-0)
74.4
Liquid UAN (32-0-0)
71.1
Liquid UAN (28-0-0)
63
Anhydrous ammonia (82-0-0)
47.1
MAP - Monoammonium Phosphate (12-51-0)
26.7
Monopotassium Phosphate (0-52-35-0)
8.4
Source: Calculating Salt Index by Dr. John J. Mortvedt

Salt Effect & Side-banded Fertilizer
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.
Salt Effect & Mid Row Banded Fertilizer
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.

Side-banding Profile - 1 Day after Seeding

Mid Row Banding Profile - 1 Day after Seeding
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 it's high toxicity.
  • 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.
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