By George Silva
Pop-up fertilizer is the fertilizer applied at planting in direct contact with the seed. There has been considerable interest in pop-up fertilizer as a way to increase early season nutrient availability to corn. Potential salt injury to the geminating seed and stand loss are serious concerns. Therefore, the safe application rate of N and K20 in the pop-up is much lower than the conventional 2X2 starter fertilizer. The total N plus 2KO rate in the pop-up should not exceed 10 lbs./A for silt loam and clay loam soils and should not exceed 5 lbs./A for sandy and sandy loam soils.
Phosphorus fertilizers generally have a much lower salt index compared to N and K fertilizers. Liquid ammonium polyphosphate (10-34-0) used as pop-up for corn at 8.6 gal/A (weighing 11.6 lbs/gal) will safely supply 10 lbs N and 34 lbs P2O5. Other clear, liquid fertilizers are being marketed for pop-up application that contains N, P and K. Please consult with the fertilizer dealer to determine the appropriate application rates for each fertilizer material.
Liquid pop-ups have some advantages over solids because it is easier to customize lower application rates. Also, based on the label, options are available for pesticides to be mixed with liquid pop-up. Proper equipment calibration is necessary to prevent crop injury (soybeans are twice as sensitive as corn to salt injury). Corn yield responses to pop-up fertilizers are influenced by soil test levels, spring weather and tillage conditions, and, therefore, not always consistent. Field testing a few strips side-by-side may provide valuable on-farm data on the merits of pop-up.
As only small amounts of nutrients are applied as pop-up, other placement methods such as pre-plant, 2X2 starter or N sidedressing should be used to provide the bulk of the remaining crop nutrient needs.
Related MSU Extension News article: "Pop-up fertilizer effects on soybean yields in 2011," Mike Staton,MSUE.
This article was published on MSU Extension News. For more information from MSU Extension, visit http://news.msue.msu.edu. To contact an expert in your area, visit http://expert.msue.msu.edu, or call 888-MSUE4MI (888-678-3464).
Silva is with Michigan State University Extension