One thing the recent cold, cold winter (or last fall for that matter) didn't do was break the drought cycle. As farmers are getting ready for planting this spring, Iowa still needs some recharge of the soil profile in much of the state.
April is almost here. Tornados in Northwest Missouri a couple nights ago remind us that we need to be aware of severe weather risks associated with spring. Recent very large field fires remind us that crop residue, dry foliage and high winds shouldn't be mixed with open burning. Following are some agronomy related topics farmers are asking questions about. Clarke McGrath, Iowa State University Extension field agronomist based at Harlan in western Iowa, provides the answers. McGrath writes the Corn/Soybean Insight each month for ISU Extension in Wallaces Farmer magazine.
Dry soil is still with us, check the drought monitor
While we don't think a lot about drought in winter months, as we approach warmer weather if timely rains don't come along this spring, we could start the cropping season behind the 8 ball. Most of Iowa is still in a drought, ranging from abnormally dry to severe. The U.S. drought monitor website has maps showing soil moisture conditions for individual states as well as for the entire nation. Click here to see Iowa.
How far "behind" are we in Iowa? "For much of the southwest and west central Iowa area, we need around an additional 4 inches to 5 inches of rain above normal in April and May to "catch up" and fill our soil profile for the planting season," says McGrath. "As farmers in Guthrie County mentioned yesterday at a meeting, we need even more than that to recharge ponds and wells. Let's hope the rains come gently in early April, get us caught up and then let us hit the fields hard in mid-April through the rest of planting. Not asking for much, am I?"
Avoid Insecticide/herbicide interactions
At winter meetings McGrath and other ISU Extension field agronomists spent some time discussing insecticide/herbicide interactions and how to avoid these problems. "We want to remind farmers about the many potentially yield damaging insecticide/herbicide interactions that can occur," he says. "This had slipped off the radar for nearly a decade with Bt corn rootworm hybrids becoming popular for planting and not as many farmers applying soil insecticides at planting," says McGrath.
"But recent rootworm resistance issues with Bt corn hybrids have many growers looking at planter-applied soil insecticides again given the large amount of corn-on-corn being grown in Iowa. We have to be very careful and strategic on our herbicide choices if we are using soil insecticides—any insecticide product with an organophosphate in it (Lorsban, Counter, Aztec, Thimet, Fortress) can have a potential interaction with many of our most popular herbicides. He suggests you click here for information on avoiding this.
Best plan of attack is to choose the insecticide of your choice to use (and there are some options without organophosphates you can consider as well), then talk to your ag chemical dealer prior to any herbicide applications, he says.
What is the best corn planting depth?
Farmers have spring fever and are working on planters and thinking ahead about planting strategies and potentially cold soil. A few have asked about planting shallower than normal this spring. The question they are asking is "Can we plant a little closer to 1.5 inch or less to get this corn out of the ground faster since it may be cold?" Here's McGrath's answer: "In my very humble opinion, but based on years of digging up corn planted from 1-inch to 5 inches deep, targeting 1.5 inches is not my preference."
So how deep should you plant? Some agronomists say "2 to 3 inches", and some say "1.5 to 2 inches". What about McGrath? "I say target 2 inches for depth of planting corn," he answers. "So, as you get off the planter to check seed spacing and depth, take a good read on where the seed is at in the soil and make sure it is at least 1.75 inches deep. And remember, that rain may (probably will) settle the soil around the seed zone and shallow-up the planting a little — so plan your depth accordingly. This is especially relevant if you happen to run your trash whippers more aggressively. Disc openers tend to work better around the 2-inch target in my experience, too."
However, he suggests your target a 2.5 inch planting depth if the soils get dry. Planting "too deep" (from 2.5 inches to 3 inches deep) isn't typically nearly as problematic as too shallow. "But I have seen some loss of stand, vigor and uneven emergence from 3 inch planting depth when corn is planted in cool, wet soils—occasionally. I see many more season long issues with shallow planted corn than deep planted corn, though."
What happens when you plant corn too shallow?
"You will run into big problems," he notes. "Such as rootless corn, sidewall compaction, poor root development, increased seed/root system mass in the herbicide zone, poor seed zone closing, the shallow seed zone can dry out, and no doubt I am forgetting some other maladies. But you see where I am going with this recommendation. You should err on the side of being too deep rather than too shallow."
NH3 application and corn planting, how long to wait?
How soon after you apply anhydrous ammonia can you safely plant corn in that field—to avoid corn injury? "We have more N to apply this spring than we have faced in probably a decade," notes McGrath. "While some areas of Iowa got a lot of field work done after harvest last fall, for the majority of farmers the fall NH3 applications were way down across much of the state, especially in southwest and west central Iowa."
This means that unless the weather is more cooperative than usual this spring, "we'll be wrapping up NH3 applications and farmers will be chomping at the bit to start planting corn." A common question is "how long do we need to wait between NH3 application and corn planting?" There isn't a set number of days—nor a firm answer to this. "Here's what ISU Extension soil fertility specialist John Sawyer says," notes McGrath.
The key is having a soil separation between the ammonia zone and the seed in the soil. Depth of injection of NH3 is extremely important. Ammonia usually diffuses 2.5 to 3 inches from the point of injection. But, if wet soil causes the injection knife to seal the sides of the injection slot and limits diffusion of ammonia, then the ammonia may concentrate below the soil covering or the soil seal. If this happens, and you place seed in the ammonia zone, the longer you wait between applying ammonia and planting corn, the less corn roots will be affected. No magic number of days of waiting will eliminate potential problems if seed is placed in the ammonia zone.
Ammonia injury is detected more frequently in dry weather, because corn roots are slow to develop and a portion of the root system is injured. "You will first notice uneven emergence, slow growth of injured plants, and in dry soil, wilting plants," says McGrath. "Browning of roots indicates root injury. In severe cases, dead roots will turn black, even back to the seed."
Key is to have soil separating ammonia zone and corn seed
If you apply ammonia at the proper depth and achieve soil separation between the ammonia zone and the seed, you can plant corn immediately after you apply ammonia.
A few things can reduce the risk of ammonia damage: wait and apply when soil conditions are good (of course, that's easier said than done); have a good injection depth (7 inches or deeper) for the NH3; wait several days after applying the NH3, until planting the corn; if the injection placement relative to future corn rows can't be controlled, apply the NH3 at an angle; if the injection placement can be controlled with GPS guidance, you can split the future corn rows—that is, apply the anhydrous ammonia in the row middles—between the rows—and no waiting period is needed between ammonia injection and planting.
"Yes, the term 'several days' is open to interpretation," says McGrath. "Two days is probably a little on the quick side, so I will say you should wait 3 to 4 days."