Pop-up fertilizers have attracted some attention recently as a way to increase early season nutrient availability to corn. Pop-up fertilizers may contain small amounts of nitrogen (N), phosphorus (P) and potassium (K). They are applied to the seed furrow at planting in direct contact with the seed. To avoid salt injury to the seed, the total N plus K2O rate in the pop-up fertilizer should not exceed 10 lbs./A for silt loam and clay loam soils and not exceed 5 lbs./A for sandy and sandy loam soils.
Liquid pop-ups have some advantages over dry fertilizers because it is easier to customize lower application rates. Michigan State University Extension field research has shown that yield response to pop-up fertilizers is not consistent. The response is influenced by factors such as soil test P and K levels, planting date, soil moisture, soil temperature and tillage conditions. Field testing a few strips for side-by-side pop-up versus check treatment comparisons will provide valuable on-farm data on the merits of using pop-up. Having at least four replications to compare the two treatments will provide the most reliable results.
For corn, liquid ammonium polyphosphate (10-34-0) used as pop-up at 8.6 gal/A (weighing 11.6 lbs./gal) will safely supply 10 lbs. N and 34 lbs. P2O5. Phosphorus fertilizers generally have a much lower salt index compared to N and K fertilizers. Proper equipment calibration is necessary to apply the right dose and prevent crop injury.
Soybeans are twice as sensitive as corn to salt injury, and therefore MSU Extension currently does not recommend pop-up fertilizer on soybeans. Also, the bacteria in the seed inoculant are sensitive to fertilizer injury, so the negatives may far out-weigh any potential benefits.
As pop-up fertilizer provides only small amounts of nutrients, other placement methods such as pre-plant, 2X2 band placement at planting, top dressing or sidedressing applications should be used to provide the bulk of the remaining crop nutrients.
Source : msu.edu