Fall Fertilizer on Grass Seed

Bob Schroeder
CPS Tangent

How much is enough? 


     When planning your fall fertilizer applications on your ryegrass, fescue, and orchardgrass, it is important to calculate how many nutrients have been removed from the previous crop in the seed and straw.

  With the amount of baled straw being removed from the fields this past harvest, it may be very surprising how much has been removed in total nutrients.  The biggest use of nutrients in the straw of course is Potash.  For a two ton straw removal of ryegrass, 80 pounds of potash is removed.  For three tons of fescue straw, 120 pounds of potash is removed.  Orchardgrass straw removal is very similar to fescue.  Based on Oregon State University work lead by Dr. John Hart, you can calculate nutrient removal in the straw for both fescue and ryegrass species by the following;  Nitrogen @ 1%, Phosphorus @ 0.1%, Potash @ 2.0%, and Sulfur at 0.2%.  Numbers for calcium and magnesium are very similar in ryegrass and fescue, with calcium running 0.3% in fescue, and 0.35% in ryegrass.  Magnesium in fescue straw is 0.18%, and 0.12% in ryegrass. 
Using these numbers for fescue straw, one ton of fescue straw contains approximately 20 pounds of nitrogen, 2 pounds of Phosphorus, 40 pounds of potash (potassium), 6 pounds of Calcium, 3.6 pounds of magnesium, and 4 pounds of sulfur.  Since most fescue straw yields between 2.5 and 3.5 tons per acre, total nutrient removal can add up quickly most notably with potash as high as 140 pounds per acre.  
These are important numbers to know as you plan your fall fertilizer programs.  Work with your CPS crop advisor to formulate a plan of attack for your fall nutrient needs based on your yields of seed and straw, and your crop production goals for the coming season, and available soil amendments and nutrients.  
 For a more detailed report on nutrient removal, check out the Oregon State Extension publication EM9051, Postharvest Residue Management for Grass Seed Production in Western Oregon.