2 O 5 side-dressed near the row may be effective in overcoming P deficiency symptoms. However, a warming period will usually allow corn to recover and seldom are yields reduced by the temporary P deficiency. Where soil test P is less than 100, recommended P fertilizer rates range from 50 to 100 pounds of P 2 O 5 per acre. Potash is recommended for soil test K levels below 275 at rates ranging from 50 to 200 pounds of K 2 O per acre. The secondary elements calcium, magnesium, and sulfur are generally considered adequate in most Arkansas soils.
Calcium is adequate for corn as long as lime needs are met.
Both elements tend to leach downward and accumulate with the clay in the sub-soil. Medium to high levels of these elements in the top-soil should be adequate for the corn crop. Both magnesium and the sulfate form of sulfur are added from irrigation water supplied by most wells. Soil tests for sulfur are not very useful in predicting plant needs. Most S in soils is in unavailable forms associated with organic matter and clay.