Fertilizer Requirements for Corn
Fertilization should be done on the basis of soil tests and yield goals. Corn requires approximately 1.25 lbs. of elemental nitrogen (N), 0.6 lbs. of phosphate (P2O5) and 1.4 lbs. of potash (K2O) to produce one bushel of grain corn. Nitrogen may be applied before planting, at planting time, as a side dressing after corn has emerged, or through an irrigation sprinkler system. Fall application of N is not recommended on sandy soils, soils subject to flooding or high water table soils.
Starter fertilizer can be applied with the planter in a band to the side and below the seed. The entire recommended fertilizer rate can be safely applied in a band 2 inches to the side and 2 inches below the seed, although N rates higher than 50 lb/acre may inhibit early season P uptake because the band may be too "hot" for plant roots until nitrification takes place. Under cool, wet conditions, starter fertilizer offers some advantage. "Popup" fertilization, the placement of fertilizer in small amounts directly with corn seed, has been used. "Popup" fertilizer application should not exceed 5-10 pounds of N, 10 pounds of P2O5 and 5 pounds of K2O per acre.
Zinc deficiency of corn is found in localized areas in North Dakota. The soil test for zinc is accurate and reliable. However, routine sampling may miss small irregular sites in fields that first appear as stunted yellow plants as zinc levels are depleted. Need for this nutrient can be corrected in a growing crop with foliar sprays. However, it is normally less expensive and more convenient to correct with dry granular products applied in the fertilizer mixture. Also, high soil phosphorous levels or high starter P levels (applied without zinc fertilizer) may magnify zinc deficiencies in low zinc soils.