Most Iowa farmers understand there is an advantage in moving from continuous corn to a corn-soybean rotation. Steve Butzen, an agronomist with Pioneer Hi-Bred International Inc. in Johnston, says a longer rotation, adding alfalfa to the mix, also will probably increase the corn yield for the year corn is grown. Plant population is another factor. Compaction also is important to consider. Butzen says research shows compaction can reduce yields by up to 25 percent.
Fertility is always important, and the first item on the fertility list is nitrogen.
Butzen says for a maximum yield, corn needs 1.25 to 1.5 pounds of actual nitrogen per bushel produced. That figure includes nitrogen supplied by manure, the previous crop or organic matter. Kirby thinks manure often makes a better fertilizer than does purchased nitrogen. Possible reasons he is considering include the interaction between trace elements and the availability of the nitrogen through the growing season. Butzen and Navratil say there is no research to support that theory.