No. 20 Article 7/August 24, 2012

Managing After Drought

The corn crop rating in Illinois stays in the low single digits, and all indications are that, apart from ongoing concerns about standability and grain quality, we more or less have the crop we're going to harvest at this point. Early yield reports are coming in about as expected, though some have reported more in-field variability than expected and yields lower than anticipated.

As the season winds down on what will go down as one of the most drought-reduced corn crops in Illinois history, a number of factors are at play that will affect how we approach management of crops in the coming year.

Some parts of Illinois have gotten rain in recent weeks, but others have received little or no rainfall; parts of the state remain stuck at seasonal rainfall totals 8 to 10 inches below normal. Where the crop is poor, it has used less than the 20 to 22 inches or so of water it would normally have used, but with the low rainfall, soil in many areas will need to take in at least 6 to 8 inches of water to recharge to field capacity.

Average precipitation between September 1 and March 31 ranges from about 15 inches in northwestern Illinois to about 30 inches in the southernmost part of the state. Some feel that we need a snowy winter to get moisture levels back. Because snow melts slowly, most of the water moves into the soil, but it is not always distributed evenly across the landscape, and relatively little of our precipitation comes in the form of snow. There seems to be some debate about whether the drought pattern still persists, but recharging soil water will need only about half the amount of precipitation we normally get during the off-season. Chances of getting that much would appear to be high. It will be better to come in smaller events so that more of it gets into the soil instead of running off.

In areas where harvest is underway, some tillage is already being done. While we often expect that tillage of dry soils after extended periods of dry weather will bring up large, hard clods, initial reports indicate that the soil is quite friable, breaking apart better than expected. This makes sense; tillage last fall and field operations this year all took place when soils were relatively dry, so there has been little of the compaction that normally results from heavy equipment on moist soils.

While rainfall does not really cause much compaction--it simply can't produce the high weight loads needed--it does cause surface soils to run together to form a hard surface that often means more water running off slopes. So expect soils to be mellower than normal during fall tillage, and match the tillage operation, if any is needed, to this condition.

The 2012 winter wheat crop was a good one in Illinois, and the loss of income from poor corn crops along with early harvest or destruction of corn will have some producers in dry areas thinking about wheat as a possible follow crop for corn. In some cases, wheat (or rye) might also be considered as a cover crop, used to take up some of the nitrogen (N) left in the soil. While having some of the leftover soil N stay in a (grass) cover crop for a following corn crop may seem like a good way to recycle N, actively growing cereal rye or wheat cover crops in the spring can be challenging to manage for establishment of a corn crop, especially if corn is to be planted in early April.

It will often be easier to manage a grass cover crop to establish soybeans rather than corn next spring, though wet soils and heavy cover crop residue can present challenges for any crop that follows a cover crop. Soybeans will use the N released by breakdown of the cover crop but will likely fix less, so there won't be much economic gain from keeping N for the soybean crop. It will, though, keep some N in the field so that less reaches surface water.

While we can't guess how much of the leftover N will be left for next year's crop, other factors associated with a drought-damaged corn crop make such fields a better place for corn next year than they would normally be. Corn that stops growing in midseason does not produce much lignin, so its residue is softer and it breaks down faster. Lower quantities of softer residue will also present less physical challenge to the planting operation.

This is not a suggestion to plant more corn and fewer soybean acres next year. Corn following corn is showing more stress effects again this year, in some areas for a third year in a row. So even though a field with a short corn crop this year may be more corn-friendly than normal next year, it is still unlikely that corn following a corn crop--even a low-yielding one--will yield more than corn following soybean.--Emerson Nafziger

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