Before he plants a single seed, Scott Rahn plans a foundation for top corn yields. He and brother Noel focus on field-by-field hybrid selection, crop rotation and seedbed preparation in their fields near Bingham Lake, in south-central Minnesota.
“Few management decisions are as important to high-yielding corn as those concerning planting,”says Jeff Coulter, University of Minnesota Extension corn agronomist. Of all the corn-planting decisions farmers make, hybrid selection has the greatest impact on yields, followed by rotation and uniform emergence.
These three variables account for up to 90% of corn yield increases, he says.
#1 Yield booster: Select optimum hybrids
Potential yield increase = 37-64%
Yield differences among hybrids are huge. In University of Minnesota corn trials, the gap between the highest- and lowest-yielding entries is usually about 50%, or roughly 70 bu./acre. In Iowa, that spread is around 60 bu./acre and in Ohio, about 40.
“There’s no other agronomy practice that affects yield as much as hybrid selection,”Coulter says.
Mike Zwingman, agronomy research leader for United Farmers Cooperative, York, Neb., agrees. “Correct hybrid placement is about as important as weather for good yields.”And corn genetics are advancing so rapidly that the lifespan of most hybrids is only three or four years, says Kelli Bassett, a Pioneer field agronomist from Greenville, Ill. “So you really have to be on your game.”
The Rahns take these steps to choose their hybrids:
Match hybrids to fields.Most years, they plant about eight different hybrids –each for a specific field. Working with agronomist Mark Hockel, Eagle Ag, Windom, Minn., they consider field drainage, soil properties, herbicide and fertility programs, previous crop, anticipated pest and disease pressures, scheduled field harvest –even where harvested grain will be stored.
Hockel sorts through hybrid trials from seed companies and third parties, identifying numbers that yielded well across a range of environments. Then he and the Rahns match plant genetics to field agronomics.
“We used to talk about ‘go anywhere’hybrids,”Zwingman says. But the “one-hybrid-fits-all"mentality is gone. Every hybrid has specific strengths and weaknesses, and we have to pay attention to where we place it.”
Prioritize traits.Along with corn rootworm traits, the Rahns’top priorities are early seedling vigor, standability and good drydown. Because they plant corn in 22-in. rows, they look for hybrids of medium height with an upright leaf, which intercepts more light.Recently, they started taking into account each field’s wind exposure. “We’ve had so many more wind events,”Hockel says. “Now, we identify fields that can better handle wind when we select hybrids.”
Consider storage and drying.When selecting hybrid maturity groups, it’s important to balance yield potential and drydown, Hockel says. On average, grain moisture at harvest increases by 0.25-0.44% with each one-day increase in relative maturity, according to University of Minnesota trials.
The Rahns plant 92-107-day corn. “We have multiple bin sites, with and without grain dryers. We place hybrids based on which storage site they are going to.”Later maturities are placed in fields headed to sites with dryers.
Zwingman, the Nebraska agronomist, suggests planting your shortest relative maturity hybrids first and longer-season hybrids later to spread out the pollination window and hedge weather risk.
Rotate for resistance. Western corn rootworms in some continuous corn fields in southern Minnesota have overcome the Bt-RW proteinCry3Bb1, one of the main sources of corn rootworm protection. Cry3Bb1 still works on the Rahns’farm, but they rotate Bt-RW traits to preserve its effectiveness.
#2 Yield booster: Rotate crops
Potential yield increase = 5-19%
“Crop rotation is low-hanging fruit growers should take advantage of,”says Coulter. Rotation boosts corn and soybean yields and cuts nitrogen (N) fertilizer requirements for corn. Field trials in Indiana and Wisconsin have shown corn yields in a soybean-corn rotation were 9% higher than those with continuous corn.
In central Illinois, the yield advantage for crop rotation is increasing, says Bassett, the Pioneer agronomist. “Continuous corn has had more issues in the last five years across a larger region. Growers have struggled to overcome the factors that drag down continuous corn yields,”such as nitrogen (N) tie-up, residue management, and disease and insect pressures.
In addition to lifting yields, rotation can help you:
Manage corn rootworms. The Rahns rotate corn and soybeans on most of their 7,000-acre operation. That helps keep corn rootworms and other pests under control, Rahn says. “We’d rather use rotation than soil-applied insecticides to manage rootworm.”
Only about 10% of the Rahns’acreage is continuous corn, mainly on high-pH ground that can handicap soybeans. For growers raising more corn than beans, Coulter advises a three-year rotation of corn-corn-soybeans. “There’s less of a yield penalty on second-year corn, plus higher soybean yields than normal.”
Improve soil productivity. Bassett works with a few Illinois growers who have recently added a third crop, wheat, to their rotation “to improve farm condition,”restore soil tilth and reduce corn residue buildup and compaction. Use of cover crops to correct compaction is garnering interest, too, she adds.
The Rahns grow about 200 acres of alfalfa. “The number one reason is for the health of the soil. Alfalfa breaks up compaction and disrupts weeds and pests. This is something our forefathers understood, and we’re starting to hear more about this.”The Rahns are targeting former continuous corn fields that have developed a compaction layer 12-18 in. down, due to manure tanker traffic. “We can’t get down that deep with tillage.”
They work with a young, local farmer, Scott Veenker, who seeds the crop in early spring and manages it. In the establishment year, they get two cuttings, followed by four cuttings in the second, third and fourth years. In the late fall of the fourth year, the stand is terminated with 2,4-D and glyphosate, then moldboard plowed.
In addition to improving soil quality, returns on alfalfa have outpaced soybeans, Rahn says, and “are close to returns on some corn fields.”Alfalfa also generates substantial N savings in the following corn crops. The Rahns take a 50% N credit for first-year corn after alfalfa, and a 25% credit for second-year corn. They also see yield boosts of 20% for corn following four years of alfalfa, and 10% for soybeans.
#3 Yield booster: Manage for uniform emergence
Potential yield increase = 5-9%
A corn plant that emerges just four hours after its neighbors will be slightly smaller all season, says Rhett Schildroth, a Williamsburg, Iowa, farmer and product manager for planter-manufacturer Kinze.
“If emergence is delayed on one in four plants by one-and-a-half weeks,”Bassett notes, “yield potential falls by 6%.”The primary causes of non-uniform emergence are uneven planting depths and poor seed-to-soil contact. Consider these tips to improve uniform emergence:
Stay off the field until it’s ready. If you don’t wait until the soil is fit to work, Bassett says, “your first field pass could cause compaction that will plague the crop the rest of the year.”
Managetillage.Because of the 2012 drought, “seedbed preparation will be really important this spring,”Zwingman says. In drought-stricken areas, the ground is very hard, even in irrigated fields, he says. Growers who use conventional tillage should pay close attention to spring tillage depth and consistency.
The Rahns employ conventional tillage on most of their fields: fall chisel plow or disk-rip, followed by one or two spring passes with a field cultivator equipped with rolling baskets that smooth and firm the seedbed.
Watch planter down pressure.It’s essential to assure correct seeding depth and adequate seed-to-soil contact, Schildroth says. “You need enough force to get the proper depth, but not so much that you compact sidewalls."
Understand field conditions. Planter tools that sense ground hardness and automatically adjust down pressure on-the-go are helpful in variable fields. The hydraulic weight transfer feature also helps ensure uniform down pressure on row units across the width of the planter.
Check planter parts.“Make sure your opening disks are not worn, and penetrate to the correct depth,”Schildroth says. Adjust the planter’s closing wheels so the soil is firmed around the seed, allowing it to absorb moisture quickly and uniformly.
Match speed to field conditions.This is critical to maintain even seeding depth. “When planting a fully tilled field or into bean stubble in the same direction as the old rows, you can go at a pretty good speed,”Schildroth says “But if it’s a no-till field, corn-on-corn or you are planting at an angle to last year’s rows, slow down.”Zwingman adds: “Excess planter speed is the biggest killer of uniform seeding depth and emergence.”
Various planter speed studies had contradictory results: In a recent Illinois study, planter speeds of up to 8 mph had no yield effect. But a 1998-1999 Wisconsin study showed yield reduction of 7 bu./acre when operating a planter at 8 mph vs. 4 mph, or about 1.8-bu. yield change per 1-mph speed increase. And a yield response to planter speed increases was detected at only 23% of Purdue study sites. The variation in results would seed to emphasize tailoring planter adjustments to field conditions. (For more on this data see http://bit.ly/OhioSeed.)
Manage residue.Uneven residue distribution leads to variable soil moisture and temperature, and non-uniform emergence, Bassett says. “Use row cleaners,”and make sure they are set properly so the soil surface is exposed to sunlight.
Maintain good drainage.All the Rahn fields are pattern tiled, which reduces compaction and produces better soil tilth. “As a result, the soil is more mellow, so we can make a better seedbed,”says Rahn.
Check seed placement.In droughty areas, “we may have trouble this spring getting consistent seed depth,”Zwingman says. “Make sure your planter is running at the correct depth, and if it’s dry, err on the deeper side –at least 2 in. or even a bit deeper.”
Check seed placement when you start planting, Schildroth adds, and check again a couple more times throughout the day, especially if soil conditions change. Interrupting planting to check seed depth is inconvenient, he acknowledges. “But it’s one of the most important things a grower can do to make sure the field is planted correctly.”
22-in. rows catch more sunlight
Scott and Noel Rahn, Bingham Lake, Minn., have planted corn in 22-in. rows for 13 years. The corn and soybean growers say narrow rows capitalize on the northern Corn Belt’s long days, shade out weeds faster and make the most of today’s advanced corn genetics. Narrow rows also give them better control of in-row seed spacing, they say.
“In the northern Corn Belt, there are more daylight hours in summer, and the more sunlight you can intercept, the more carbohydrates and yield you can produce,”says Scott Rahn. As he sees it, “Any time sunlight reaches the soil, that’s wasted energy.”
Narrower rows canopy early, which “helps control weeds and also conserves moisture,”he says. And with Roundup Ready crops, “there’s no need to row-crop cultivate, which is more difficult in narrow rows.”
The Rahns plant 36,000 to 38,000 seeds/acre, aiming for ear counts of 33,000/acre. With 22-in. rows instead of 30-in. rows, the seed meter runs more slowly, “so we feel seed spacing is more accurate.”
One of the drawbacks of 22-in. rows is higher equipment cost. Narrow-row corn tends to grow taller, “so there’s more residue to manage.”The dense canopy also makes the crop more susceptible to plant diseases, Rahn adds, so a foliar fungicide application is part of their regular corn management plan.
Pioneer studies of narrow-row corn over 13 years have found considerable variation in corn yield responses to 22-in. rows, says Steven Butzen, Pioneer research agronomist. The same is true of university narrow-row studies, he says. Positive responses to the practice are most likely north of the 43rd parallel, which runs through Madison, Wis., Mason City, Iowa, and Yankton, S.D. Yield increases in the northwestern Corn Belt have averaged 4%, Butzen says. But in the central and southern Corn Belt, yield responses have been inconsistent and sometimes negative for rows narrower than 30 in., Butzen says.