Nitrogen, applied now, will help promote fruit bud development. A general application rate is ½ to 3/4 pound of actual nitrogen per 100 feet of row. The nitrogen may be in the form of a fertilizer mixture such as ammonium phosphate or 12-12-12, or in a fertilizer containing only nitrogen such as urea or ammonium nitrate. Some specific examples would include:
Iron + (11-0-0) at 6 pounds per 100 feet of row. 12-12-12 at 5.5 pounds per 100 feet of row.
Nitrate of Soda (16-0-0) at 4 pounds per 100 feet of row
Ammonium sulfate (21-0-0) at 3 pounds per 100 feet of row
Urea (46-0-0) at 1.5 pounds per 100 feet of row
On sandy soils, the rate may be increased by about a half.
After spreading the fertilizer, water the area applying at least a half-inch of water to move the nitrogen into the strawberry root areas. (Ward Upham)