Fertilization
Nitrogen
A general range would be from 150 to 275 pounds per acre, depending on plant population and previous crop.
Many growers prefer not to apply preplant nitrogen prior to planting because this operation can cause the seed bed to dry out and not have good moisture for germination. In fields with low nitrogen reserves it may be desirable to apply a portion of the nitrogen preplant. Do not inject ammonia directly below where the seed row will be planted. Corn needs only 2% of its nitrogen during the first month. Most of the nitrogen is absorbed 6 to 12 weeks after planting. A common practice is to use a starter fertilizer at planting and then sidedress. The starter fertilizer should contain about 10 to 15 pounds of nitrogen, with phosphorus and a small amount of zinc.
The nitrogen sidedressing should be applied before the corn is 1 foot tall. The nitrogen in the starter should carry the corn to this stage with no nitrogen deficiency occurring. Stay 8 to 15 inches away from the plants with the sidedressing knives in order to reduce the amount of root pruning and injury from ammonia. The safest source of nitrogen for sidedressing is UN32 solution.
Soil Analysis
Growers should use soil analysis to evaluate the availability of the fertilizer elements phosphorus, potassium, and zinc.
Phosphorus
Most growers prefer to apply their phosphorus in a nitrogen phosphorus starter fertilizer to obtain vigorous, early growth. Starter fertilizer is best banded 2 inches below and 2 inches to the side of the seed.
Phosphorus, in a starter fertilizer, is usually applied at 10 to 26 pounds of P per acre (20 to 60 P₂0₅) with 10 to 20 pounds of nitrogen. Soil tests for phosphorus may not be reliable following several years of rice or on very low pH soils. A yield response is likely with soil levels below 6 ppm phosphorus and not likely with levels above 12 ppm, using the sodium bicarbonate method of analysis.
Potassium
To date, deficiencies on corn have only been found in a few areas of the state. In the Clarksburg area, the starter should contain potassium. Responses have been obtained with soil values in the range of approximately 70 to 90 ppm potassium, using the ammonium acetate method of analysis or less than 200 ppm by nitric acid extraction. Trials have shown that 20 to 40 pounds per acre of banded potassium (K₂O) would be sufficient for most of the deficiencies encountered. Broadcast applications of potassium have not given good responses when compared to banding.
Zinc
Zinc deficiency is widespread in Yolo County and may occur anywhere in the state. This deficiency is commonly found as spots of various sizes in a field. Zinc deficiency on corn often shows as a broad band of white or yellow tissue between the mid-rib and edge of the leaf or as a chlorotic striping. It occurs mainly in the lower half of the leaf and may be seen when the young leaf is coming out of the whorl. Severely deficient plants are also stunted and have short internodes. The critical range for zinc is 0.4 to 0.6 ppm zinc in the soil, using the DTPA method of analysis.
Zinc fertilization of field corn can be accomplished by the 3 following methods: broadcast and incorporate before planting; with starter fertilizer at planting; and as a foliar spray on small corn seedlings.

1. Broadcast Application. The sources commonly include zinc sulfate, zinc oxide, and zinc nitrate. Suggested rate: 10 to 20 pounds per acre.
2. Starter Fertilizer. The sources commonly used include zinc su1fate, zinc oxide, and zinc chelates. Suggested rate: 5 pounds per acre for sulfate and oxide forms. A smaller amount may be used with chelates. Some fields in past seasons which used standard starter fertilizers with low zinc content of 1/2% to 1/4% showed zinc deficiency symptoms.
3. Foliar Spray. The sources commonly used include zinc sulfate and various zinc chelates. Suggested rate for zinc sulfate is 3 to 4 pounds per 100 gallons of water with a little spread-sticker at the rate of 20 to 40 gallons per acre, depending on the size of the corn seedlings. The solution should be tested on a few plants before treating the whole field, as excessive concentrations may cause foliage burn within a few hours or overnight. For chelates, follow the directions on the label.