Vegetables and Ornamental Horticulture : Fertilizing Mulched Fields

FERTILIZING MULCHED FIELDS - ARE YOU APPLYING TOO MUCH?

Stephen Reiners
Associate Professor in Horticultural Sciences

If you need to broadcast fertilizer prior to planting, it is relatively easy to figure out how much to apply. If you are using plastic mulch, however, you may be applying more fertilizer than you need. In a typical mulched field, the width of the soil surface covered with mulch is usually three feet. The uncovered area is usually 2 to 3 feet depending on the row spacing. For our example, lets use two feet. Prior to laying plastic you need to add 50 pounds of N and 100 pounds of P and K. Using a 10-20-20 fertilizer you could spread 500 pounds evenly across the acre. But you will be fertilizing the area that is between the rows, an area where crop roots will likely not be feeding but weeds will. If you have the equipment, it is much better to apply the fertilizer only to the area that will be covered with mulch. Since that will be only three feet of every five feet, that means that only 60% of an acre will be used by the crop. You can cut your fertilizer rate to 300 pounds per acre from 500 and still get the same effect. Once this is applied and the plastic is laid, you can use the same calculation to apply fertilizer through the drip system. If you need 20 pounds per acre of N, P, and K and are using a 20-20-20 soluble fertilizer, you will need only 60 pounds of fertilizer rather than 100 pounds,

It all comes down to the fertilized-mulched acre. This is the percentage of an acre that is covered by plastic mulch where most of the crop roots will be found. Applying fertilizer based on this will save you money and maintain your crop's quality.