Gordon Johnson, Extension Vegetable & Fruit Specialist; firstname.lastname@example.org
The first sweet corn has been planted on plastic and bare ground plantings will be starting soon. This is a good time to revisit starter fertilizer use in sweet corn.
Sweet corn does respond to starter fertilizer. Of the nutrients that can be provided in a starter fertilizer, research has shown nitrogen (N) and Sulfur (S) to be the most beneficial, followed by phosphorus (P). In sweet corn it is common to include all 3 in starter fertilizer, although P does not always show a response.
We are starting to see some potassium (K) deficiencies in sweet corn on Delmarva. K in starter can be beneficial but rates should be limited. If soil K levels are high, K in starter fertilizer is not necessary.
We usually do not see a response to boron (B) in sweet corn so it is generally not recommended in starter fertilizer. Fields that receive B broadcast applications (1-2 lbs/A) at least once every 2 years should have sufficient B for sweet corn growth. If B has not been broadcast in the rotation it can be added to starter fertilizer but the rate should be very low to avoid B toxicity (1/8 lb/A, or less).
Zinc is usually not added to starter fertilizer for sweet corn except on high pH soils or soils with excessive P.
It is important to be careful in how close you place starter fertilizer to the seed (a concern with sweet corn starter fertilizer is reduction in stands due to fertilizer salt injury). The standard recommendation is to place starter fertilizer 2″ to the side and 2″ deep. This provides a concentrated band for early uptake (plant roots will proliferate around the band); and the band will be far enough away not to cause salt injury to germinating seedlings. Do not use pop-up (in seed furrow) fertilizers with sweet corn because there is too much risk of salt injury.
Suggested rates for starter fertilizer nutrients in sweet corn are shown below:
N = 20 lbs/A (10-20 lb/A range)
P = 20 lbs/A (15-20 lb/A range)
K = 10 lbs/A (10-15 lb/A range) only if K is not testing high in soils
S = 10 lbs/A (10-15 rlb/A ange)
Zn = 1 lb/A (none if Zn levels in soil are sufficient)
B = 0.125 lbs/A (none if you apply broadcast B in previous crops).