Dry weather increases risk of starter fertilizer damage

Here’s a pop quiz on pop-up fertilizer:

In a dry year, which can cause damage to corn when placed with or very close to the seed?

  • salt
  • nitrogen
  • ammonium Sulfate
  • boron
  • all of the above

The answer is “all of the above,” says Daniel Kaiser, University of Minnesota Extension nutrient management specialist.

Here’s Kaiser’s rundown on the risks:

All fertilizer contains salts, and salts have charged ions that attract water. The higher the concentration of salt, the harder it holds water. In a dry spring, salt makes it difficult for the roots to take up water. In severe cases, a corn plant’s radical, or the first emerging root, will be killed off. Fields exhibiting damage will have very uneven emergence, and the plants that do emerge may be spindly in appearance.

If you dig the plant, the radical root will typically be short, and the tip will be brown or black. Plants may recover by growing new roots, but typically, they have been set back significantly enough that yield reductions are highly likely. At this time fields will have to be assessed for possible replanting if the damage is severe enough.

Key Points

• Dry spring will increase risk of damage from improperly placed starter fertilizer.

• Salts, nitrogen, ammonium sulfate ions and boron are all dangerous to seed.

• Keep at least 1 inch of soil between fertilizer and seed to reduce risk.

The amount of N in the starter may have a larger impact than salts. Urea poses the highest potential risk since ammonia is liberated as the urea molecule is being converted to a plant-available form. Check to see what the percentage of urea N is in starter mixes since this can significantly affect when damage occurs.

Thiosulfate ions, found in ammonium thiosulfate fertilizer, can damage corn roots. Low ATS rates may not seriously reduce stand in loamy soils but will reduce plant growth when soil moisture is near capacity. Surface banding ATS to the side of the row can be effective and greatly reduce the risk for stand damage compared to applying with the seed.Boron can cause more damage than sulfur or N in a dry year.

Solutions

Use 2x2 placement — or any other method that gets at least 1 inch of soil between the seed and fertilizer band — to reduce the risk of damage to corn seed in a dry year.

“There is not a 100% safe source of fertilizer for pop-up placement,” Kaiser says. “Knowing the risks is important to ensure the best possible outcome and even emergence after planting.”

University of Minnesota Extension Service contributed to this article.

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This article published in the January, 2013 edition of DAKOTA FARMER.

All rights reserved. Copyright Farm Progress Cos. 2013.