These handy diagrams from Agvise Labs show how far apart dry monoammonium phosphate (MAP) granules are in the seed row when applied at five, 10, 15 and 20 pounds of P2O5 per acre. At the five-pound rate, distance between granules is 7.6 inches. This is for seed openers on seven-inch spacings.
Because phosphorus doesn’t move very far, that means most seedlings won’t have access to the granules. When you increase the rate to 10 pounds, the granules are 3.8 inches apart. That’s better. At 15 to 20 pounds, there’s a granule for every seed — more or less.
John Lee, a soil scientist with Agvise, says “It seems like such a simple thing, but most growers who want to cut the rate of fertilizer they use as a starter, do not consider how far apart the dry fertilizer particles or drops of liquid fertilizer are from the seeds at low rates. Research shows that each seed needs to have fertilizer within one to two inches to get the starter affect that we need in our normal cool spring conditions.”
To see the strips for liquid fertilizer and for other crops, including wheat, go to www.agvise.comand click on “New Starter Fertilizer Distribution Display” on the right side of the home page.
Lee reminds you that for wider seed row spacing, the granules and droplets will be closer together if you maintain the same fertilizer rate per acre. If granules are 3.8 inches apart when applied at 10 pounds of actual per acre on seven-inch rows, then granules will be only 1.9 inches apart if your seed row spacing is 14 inches.