“North Carolina growers should not manage for average corn yields, because average is not profitable,” said North Carolina State University corn specialist Ronnie Heiniger.
Speaking at the recent North Carolina Corn Producers Association meeting, Heiniger said there are five basic keys to managing a corn crop for high yields.
First, he said is to select high-yielding hybrid varieties that have a history of high, uniform stands and yield stress tolerance. Heiniger pointed out that 70 corn growers in North Carolina were recognized at the annual meeting for producing 200 bushels or more per acre and that one consistent variable among their production practices was use of proven varieties.
After selecting the optimum variety, it is critical to plant enough seed to get an optimum stand without wasting money on overseeding. Seed cost is a variable often not managed well by corn growers, Heiniger said.
Though many production factors influence precise seeding rates, in statewide testing on sandy soils, the optimum seeding rate was 40,000 seed per acre. On heavier soils with more organic matter, 35,000 seed per acre provided maximum yields, Heiniger explained.
Depending on soil dynamics and other factors, growers can adjust precise rates up or down from these average rates, Heiniger said. In 2005, the state yield champion, Hardy Farms, planted 35,000 seed per acre and runner up, Justin Carter, planted 24,000 seed per acre. Row spacing of 30-inch versus 20-inch for the top producer is one factor accounting for the difference in seeding rates.
A simple thing like planter calibration can play a bigger role in reaching yield potential than most growers think, Heiniger said. “Calibrating the seeder correctly is simple and doesn't take a lot of time, but not paying attention to this detail can be the limiting factor in reaching 200 bushel per acre yields, the North Carolina corn specialist said.
The optimum seed spacing for 30-inch rows is 6 inches, he noted. Research demonstrates that every 1-inch variation from the standard deviation caused a 5-bushel per acre drop in yield in field testing in 2005. “When you see a corn field with some plants bunched together and others with wide plant spacings, it's easy to see how a grower can lose 35 to 40 bushels per acre just from poor planter calibration, clogging or other mechanical problems that can easily be avoided,” Heiniger stressed.
Quick exploitation of the vertical root system is another key to producing 200-bushel-per-acre corn, Heiniger said. In addition to the cost of yield reductions, the high cost of fertilizer makes it doubly important for growers to choose the optimum starter fertilizer that gives corn plants the best chance to establish a strong root system.
Proper fertilization is the last key, though it directly affects the other four. “How do we respond to higher fertilizer costs is a question every corn grower is asking, Heiniger said. For growers trying to make maximum yields it is another of those two-edged swords — on one side using enough fertilizer to make maximum yield, and on the other side, not using more than is needed.
Richard Reich, assistant commissioner of agriculture in North Carolina, said state labs completed over 300 corn tissue analyses in 2005, and surprisingly, more samples showed low and deficient sulfur than nitrogen.
Heiniger agreed that low sulfur in 2005 was a more limiting factor on corn yields than nitrogen. Though stopping short of recommending grid sampling in corn fields, the North Carolina State specialist did urge growers to test more thoroughly in low-producing areas of their farm to ensure adequate use of sulfur and other fertilizers.
Potassium is another critical factor affecting corn yield. Heiniger pointed out every 100 pounds of K applied to a corn field, takes $6.25, or about 3 bushels of corn to pay for it. “Growers can't cut back on K and expect to produce a top yield, yet in the overall budget for fertilizer there is a set amount for potassium. Thus, putting K in the places in a field where it will do the most good is critical to both yield and profitability.
Determining precise amounts of fertilizer to use is critical in that fertilizer prices are high and corn is a high-demanding crop. The best approach, according to Heiniger, is to use 25 to 50 pounds of N at planting, then use a simple color test, in which small strips are analyzed to determine which areas of the field used the N and which areas need additional amounts.