How much fertility can you afford for your 2010 corn crop?

You still start with the basics and that means soil tests to give you a baseline on nitrogen, phosphorus and potassium. But agronomists also suggest getting a zinc reading, maybe even sulfur even though soil tests are not as reliable for this nutrient.

“Sulfur readings depend much on your organic matter levels. Below 2 percent OM and you have good response from sulfur. But growing evidence is suggesting that sulfur should be a basic item since organic matter is such a variable, even within the same field,” said Dave Nicolai, University of Minnesota Extension crop specialist.

U of M soil scientist Dan Kaiser said, “the corn plant needs sulfur in amounts similar to phosphorous. Typically your soil’s organic matter, through mineralization, provides sulfur. Also some gets deposited from the atmosphere. But we’re seeing significant yield response from additional sulfur, especially on soils in southeast Minnesota. Even at Clarks Grove we got a 15-bushel response from 25 pounds sulfur added with starter N.”

Soil scientist Gyles Randall, Southern Research and Outreach Center at Waseca, speaks directly about sulfur.

“If I was a grower and owned my own land, with the relatively cheap price of sulfur I’d be putting on a blanket, prophylactic application. You minimize your risk and optimize your returns, especially in those years when we’ve got high yields.”

Larry Arentson, agronomist for Co-op Country’s Olivia fertilizer warehouse, said sulfur has been a routine ingredient in most of their customer’s fertility programs for several years. In his area, soil pH readings of 7.6 or higher are the norm and organic matter contents typically run 3.5 percent and higher.

“It boils down to the simple fact that as yields keep getting bigger, we’re mining even the micro-nutrients out of our soils. So supplemental sulfur and zinc are pretty much standard procedure with most farmers,” Arentson said.

He adds sulfur three ways:

  • Granules of elemental sulfur (90 percent sulfur) with 11 pounds providing 10 pounds actual sulfur;
  • Adding liquid sulfur to a 6-24-6 liquid starter; and
  • Using 10-34-0 liquid with both sulfur and zinc added to the solution. A new product by Mosaic called MicroEssentials-SZ with a 12-40-0-10S-1Zn label has become popular.

He said, “with this product you’re getting a convenient package for handling both your phosphorus needs and your elemental sulfur and zinc. For example, 200 pounds of this product gives you 80 pounds phosphorus and 20 pounds sulfur. At the rate of 100 pounds per acre the cost is about $20 per acre.”

So as corn yields keep climbing should you stick with basic fertility recommendations and just add more fertility? Randall said, “growers adding more fertilizer as yields increase are directionally correct. But efficiency and economics might be questioned.”

Think long term

He thinks fertility recommendations need to be tailored to land tenure and the “investment philosophy” of the particular farmer. “If the producer is long term on particular fields, fertility recommendations should be geared accordingly. That may not be most economic in that first year but long term will minimize risk and maximize profitability. Those producers who rent and are cash short are better served by yearly applications that maximize first-year profitability.”

Does that suggest it’s getting easier to make a case for continuous corn? Randall thinks so, especially when establishing long-term fertility programs. But he recognizes that many farmers will face big challenges this spring, especially if they didn’t get fall tillage and fall fertility work taken care of.

“If you’ve got corn following soybeans, you should have a good chance of ‘resurrecting’ yourself, assuming spring weather is OK. But with corn following corn the challenge is handling the residue. I’m not big on using the disc but some combinations of shallow ripping and double disking may be needed. We know that no-till corn on poorly drained soils is a recipe for disaster. But soybeans no-till planted into corn stubble sacrifice only a couple bushels yield. It will look a little ratty at the beginning but our work shows no-till beans into corn performs quite well,” Randall said.

Split applications a better way?

“We find that when we split our N applications, especially if that second application is by V3 or earlier, we minimize risk. Delay later and the N may not be getting into the root zone soon enough to contribute to additional yield,” Randall said.

Does this suggest the Green Seeker technology, which “reads” leaf color to adjust side-dress N applications on the go?

Randall thinks the technology better works under irrigated conditions, which allows nitrogen to be put on a little later in the season and get it “watered in” via the irrigation equipment.

“We’ve been testing it for five years now and our challenge under ‘rain-fed’ conditions is that the sensing device on corn following soybeans can’t distinguish between those areas needing supplemental N and those not needing extra N until the corn gets into V9, V10 stage.

“Put nitrogen on at that stage, even if we incorporate it a few inches, we often don’t get enough rainfall to move the nitrogen down into the root zone where it is needed to feed the growing corn plant.”

Randall said that if he were a grower he would rely on pre-plant “for most of my N needs, and split apply only if I can get that second application before corn is knee high, V3 being most preferred.”

He suggested, however, that for fields highly variable in organic matter, Green Seeker technology might be a convenient help. Another nutrient item is also creating some challenges.

“Sulfur deficiencies also leave a lighter-colored corn leaf so the sensor may not be correctly identifying the nitrogen deficiency. Maybe we go to blanket applications of sulfur as a remedy.”

Corn stover harvest

Harvesting your stalks for bedding, or potentially for biomass energy creates additional fertility challenges. The amount of dry stover produced by a corn crop is about equal to the weight of grain at 15-percent moisture. That means a 150-bushel corn crop would leave about four tons of stover in the field. Typically, about 60 percent of stover is collected or about 2.5 tons per acre.

Each ton of dry stover contains about 3.6 pounds of P2O5 and 20 pounds of K2O. That translates into a loss of nutrients valued at roughly $44 per acre or $18 per ton of stover removed.

In addition to economic losses, stover harvest removes important organic matter and risks compaction in soil profiles.

So if stover harvest is a must, consider replenishing lost nutrients for next year’s crop.

Nutrient management planner

University of Minnesota Extension is offering Nutrient Management Planner V3. This $50 easy-to-use software program helps producers and agronomists plan and keep records of field-specific fertilizer and manure applications.

With it, you can quickly access current U of M fertilizer recommendations of each field, including the new nitrogen recommendations for corn. Call (800) 876-8636 and order product 08631.