Low Salt FAQ
Q. What does “low salt” refer to?
A. Liquid pop-up fertilizers are also commonly referred to as “low salt” or “seed safe” formulations. Potential sources of salt are the nitrogen, potassium and sulfur components in liquid fertilizers.
Q. What sources of nitrogen (N), phosphorus (P) and potassium (K) are present in pop-ups to make them low salt?
A. Nitrogen forms in seed-safe starters are typically ammonium or urea. Phosphorus sources can be green super phosphoric acid, white food grade acid or monopotassium phosphate. Potassium sources are typically potassium hydroxide or monopotassium phosphate. Phosphorus applied in-furrow at moderate rates, whether in a poly or orthophosphate form, does not contain enough salt to pose a threat to germination.
Q. What is the difference between orthophosphate and polyphosphate and is one better than the other?
A. Orthophosphate is a single phosphate molecule. Polyphosphate is a chain of orthophosphate molecules. When polyphosphate is in the orthophosphate form, it can be taken up by the crop or tied-up by the soil. Polyphosphate molecule chains must hydrolyze (or break apart) into separate orthophosphate molecules in order to be plant available. However, the poly chains will convert to ortho after they are applied to the soil.
Research shows that all added polyphosphate is typically hydrolyzed to ortho within days from soil application, and is enhanced by warm soil temperature, moisture content, soil pH and biological activity. Water-soluble poly products convert to ortho more quickly.
Q. How much actual plant food am I applying in 5 gallons of 9-18-9?
A. 5 gallons x 11.15 lbs per gallon = 56 lbs of product.
X 9% N = 5 lbs N/acre
X 18% P = 10 lbs P/acre
X 9% K = 5 lbs K/acre
Q. How do I evaluate the cost of various low salt products?
A. For example, if you are purchasing a 9-18-9 by the gallon, at $3.00 per gallon x 5 gallons/acre = $15.00 per acre for plant food applied at 5-10-5 per acre.
Q. Is pop-up fertilizer more readily available that I can produce a corn crop with a small amount or low rate of nutrients?
A. No, 53 pounds of phosphorus (P205) and 75 pounds of potassium (K20) are removed by the corn seed harvested in 200 bu. per acre. Those nutrients have to be supplied to the crop from somewhere whether it is from starter fertilizer, broadcast fertilizer, manure, or the soil test reserve.
Q. If my planter is equipped to apply starter at 2 x 2, out of the furrow, do I need a low salt pop-up?
A. It is up to the grower. Placing a traditional liquid form starter at 2”x2” allows plant food (plus sulfur) to be safely placed with less risk of salt injury.
Traditional 2×2 products are typically more economical than seed-safe products designed for in-furrow placement. Some growers feel that having 3 gallons of seed-safe starter in-furrow and 8-15 gallons of traditional analysis plus sulfur and zinc at 2×2 provides a “one-two punch” of fertility. This can ensure early growing season uptake of nutrients, as well as using the seed safe product to carry a plant growth additive and liquid insecticide if desired.