No. 23 Article 8/October 8, 2010

What Ailed Corn Following Corn in 2010?

While corn yields in many parts of Illinois are less than we had expected and much less than we had hoped, corn following corn took a particularly hard hit in many areas. Because our current crop acreages in Illinois are skewed toward corn, at least 20% of the corn in Illinois in 2010 followed corn. So the effect of lower yields of corn following corn is not trivial.

This follows a period of several years during which corn following corn has yielded as much, or nearly as much, as corn following soybean. Anecdotally, many producers, especially those in the corn-rootworm-variant areas of Illinois, have found yields of corn following corn to be as high as those of corn following soybean, especially since the advent of rootworm resistance traits in hybrids in 2006 and 2007. For many of these producers, lower yields of corn following corn come as a shock.

Some people distinguish between "corn following corn" and "continuous corn," with the former often referring to second-year corn (following soybean two years earlier) and the latter to corn that follows at least two years of corn. Our research shows that second-year corn tends to yield a little more than continuous corn, but we have not been able to determine if that calls for differences in management. Nor do we think that second-year corn fared much better than continuous corn in 2010.

We all breathed a sigh of relief when April weather was good and we were able to plant the corn crop on time. But the middle two weeks of May were cooler and much wetter than normal, and we think it's likely that this period set the crop up for some of the problems that it experienced.

Corn following corn seemed to struggle from the start, and in many fields it never looked very good during the season. Compared to corn following soybean, emergence was uneven, crop color was not very good, and the crop seemed to struggle to take up enough nitrogen to grow well, regardless of N rates and management. With May and June so wet, many who waited to apply N until after planting struggled to get N applied on time; in these fields, N availability when the crop needed it was an issue.

Following is a list of factors that I believe may have contributed to the problems of corn following corn in 2010:

  1. Even where tillage was done last fall, soils were too wet to do a good job, and more than the usual amount of residue remained on the surface, where it affected planting and early growth.
  2. Soils were very wet, and fairly cold, coming into April. Some people who couldn't do primary tillage in the fall tried to do some before planting, but soils were never in good shape to do this, and it both created more compaction and left a lot of residue on the surface.
  3. Even though there was a nice stretch of weather in April to get the crop planted, soil conditions in fields following corn were not very good, and in fields where preplant nitrogen was applied and/or more tillage was done, soil conditions were probably even worse, with compaction added to cold and (still) fairly wet soils.
  4. Soil temperatures didn't start to increase until after mid-May, which meant after the corn crop was up-and in many fields already uneven and sickly looking.
  5. We think that corn plants following corn in cool, wet soils tend to be affected a lot by where their roots are in relation to last year's residue, including root remnants. A lot of the residue even in tilled fields was not buried very well, and it's not hard to imagine that a lot of new-crop roots were close to a lot of old-crop residue. We think that's a negative, perhaps due in part to allelopathy, perhaps from temperature effects, and maybe from some diseases that can carry over. Allelopathy starts with the release of substances as crop residue starts to break down, and it diminishes over the course of breakdown. Residue after the fall and winter was unusually well preserved into the spring in 2010, and this could have contributed to the problem.
  6. Tilled corn on corn fields likely took in more of the rain that fell in May and June, and such soils were cooler, which reduced evaporation rates and resulted in a longer "soak" than where corn followed soybean.
  7. From a combination of numbers 5 and 6, I think that roots were damaged early, and they may never have recovered fully. This probably reduced the ability of root systems (which got really wet during June, probably damaging them even more) to take up water and nutrients, including extra nitrogen.
  8. Once soils started to warm up, we expect that old-crop residue, which was still lagging in its breakdown, started to tie up nitrogen quickly. The crop was growing fast by then and needed a lot of nitrogen, which would have been slow to release from what was tied up in the residue. With tasseling coming early, it's likely that release of nitrogen from residue was too late to do much good.

Both corn following corn and corn following soybean suffered, we think, from having root systems damaged badly by excessive water. This meant that plants couldn't take up enough water even during July, which led to kernel abortion. Then when it turned drier and warmer in August, the crop simply ended, with filling rates lower than expected during much of the grain-filling period.

We'll be giving more thought to this in the coming months as we see the data from our trials. Because of the importance of continuous corn and the questions about it raised this year, I would appreciate getting comments regarding other factors that readers might have seen this year.--Emerson Nafziger

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