Figure 1. Example illustrations of starter fertilizer placement with respect to the corn plant. Graphic by Dorivar Ruiz Diaz, K-State Research and Extension.
What are the risks with “pop-up” placement?
If producers apply starter fertilizer with the corn seed (“pop-up” in-furrow), they run an increased risk of seed injury when applying more than 6 to 8 pounds per acre of N and K2O combined in direct seed contact on a 30-inch row spacing (Table 1). Nitrogen fertilizer can result in salt injury. Urea-containing fertilizers can also result in ammonia toxicity. Urea converts to ammonia, which is very toxic to seedlings and can significantly reduce final stands (Figure 2).What is a “salt”?
“Salts” are ionic compounds that result from the neutralization reaction of an acid and base. Most fertilizers are soluble salts (e.g., KCl from K+ and Cl- ions). Salt injury can occur when fertilizer addition increases the osmotic pressure in the soil solution (due to an increase in salt concentration) around the germinating seed and roots. This can cause plasmolysis, which is when water moves out of the plant cell, shrinking cell membranes and collapsing the cell. Symptoms of salt damage are short, discolored roots and a reduced corn population.
Figure 2. Symptoms of ammonia toxicity from urea-containing fertilizers placed too close to the seed. Photos by Dorivar Ruiz Diaz, K-State Research and Extension.
Table 1. Suggested maximum rates of fertilizer to be applied directly with corn seed for "pop-up" fertilizer.
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Pounds N +K2O (No Urea or UAN)
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| Row Spacing (inches) | Medium-to-Fine Textured Soil | Sandy Soil |
| 40 | 6 | 4 |
| 30 | 8 | 6 |
| 20 | 12 | 8 |
