Issue No. 2, Article 5/April 1, 2005
Gearing Up for Wheat and Corn in 2005
The wheat crop planted in Illinois last fall is estimated at 650,000 acres, the lowest number since record keeping began in 1866. Planting progress last fall was slightly behind normal for the first half of the crop, with about 50% planted by about October 17. Wet weather in October slowed progress after that, and an estimated 20% remained to be planted after the end of October. It's reasonable to assume that some of these acres did not get planted at all, but there was more late-planted wheat in the fall of 2004 than we normally have.
Wet weather continued through January in most places, with temperatures about average. Some damage occurred due to standing water, and growth of the crop was no better than average before it went into dormancy. Most of the crop appears to have survived the winter, and dry weather in March has helped the crop to recover some, though low temperatures have limited the amount of tiller growth. Dry surface soils and moderate temperature fluctuations have perhaps reduced the potential for heaving in most fields, but it may be a problem in some areas. Heaved-out plants can survive and grow back, but the need to grow back most of their root system might compromise their ability to sustain high growth rates, at least temporarily.
Having more tillers develop in the spring is especially critical for late-planted wheat. Using a conservative estimate of 1 bushel of yield for each head per square foot, we think that a normal stand of 25 to 30 plants per square foot needs at least two productive tillers (heads) per plant to have reasonable yield potential. Most early-planted fields have such tiller numbers by now, especially in southern Illinois, where slightly higher temperatures have allowed more spring growth. Late-planted wheat may still need to develop a few more tillers in order to have reasonable yield potential. The amount of spring tillering is mostly determined by the weather, with temperatures in the 50s and 60s and lots of sunshine, best for tiller formation. A sudden onset of temperatures in the 70s will often stop tillering and cause the plant to grow upright and so could reduce yield potential if tiller number is an issue.
Wheat plants will start to take up nitrogen slowly as growth resumes, but there is little actual proof that applying more than normal amounts of nitrogen early to cause more tillers to form can increase head numbers and yields. For most wheat fields in the southern half of Illinois, using a total of 100 to 110 lb N per acre (fall plus spring) should be adequate. Higher organic matter soils in northern Illinois often produce highest yields with 20 to 30 lb less N than that. Splitting spring N into two applications has not been shown to increase yields consistently, though wet weather in April might cause enough N loss that a supplemental application might pay. As a rough guideline, we would not suggest considering supplemental application unless the crop shows N deficiency as it nears heading, and then would suggest no more than 30 to 40 lb of additional N.
Corn: Time to Plant?
Dry weather during March has thoughts turning to corn planting, especially after 2004, when planting started and ended early, and yields were record-high in Illinois. There are a few points to keep in mind as we move into April:
- Data on planting date responses are not very numerous, but we continue to think that, on average, corn planted the last 10 days of April will yield a little more than corn planted the first 10 days of April. This difference is not large enough to suggest that corn planting should not start in early April, but remember that good conditions early in the month usually mean a greater chance for good conditions later in April as well. Doing other operations to prepare for planting thus might be better than actually planting the first week or two of April, especially in the northern part of Illinois. (As a note, we are starting a study of planting date x plant population this year and have already planted at one or two locations, so we should have more information on this topic over the next few seasons.)
- The main reason that early planting worked so well in 2004 was that May was warmer than usual; corn planted in early April in 2004 experienced early-season weather conditions much like those encountered by corn planted in late April in years with average May weather. Expecting May 2005 to be like May 2004 is a gamble unless you believe that global warming is here to stay.
- While March has been dry, it has been cooler than average and cooler than it was in 2004. While we don't pay a great deal of attention to soil temperature for corn planting once the calendar turns to April, soil temperatures in the low 40s and morning lows in the 30s mean that corn will take weeks to emerge, and then will do so only after soil temperatures start to rise. Taking a long time to emerge may not be a problem if it stays relatively dry, but the expected decrease in uniformity of emergence and the chances of rainfall causing soils to be both wet and cold represent risks.
- It is especially critical with early planting to have the soil in good shape to plant. High rainfall during this past winter left most soils close to field capacity (water held against gravity) throughout most of their profile, even if the surface seems dry. Soils are compacted by driving on them when they are at field capacity, even if the top few inches are dry enough to produce a good seed bed. Turning up the top 8 inches with a shovel might help show how dry the soil really is in the zone where most roots will form. This may be especially important when planting corn following corn and where extensive tillage was done last fall or earlier this spring. Corn following corn seems to encounter stress sooner than corn following soybean, so soil compaction before planting should be avoided as much as possible.
- Very early planting can present challenges for herbicides and insecticides to remain active long enough to get the crop past vulnerable stages. This should be taken as an additional "cost" against early planting, though what such costs might be is not easy to predict when the weather is so unpredictable.
- Research results have not provided much reason to adjust seed drop rate depending on time of planting. Plant populations should be high enough to produce top yields. For most productive fields in Illinois, that means harvest populations around 30,000. In a study we have under way, 40,000 plants have usually been yielding less than 32,000 in corn following corn, so we need to be careful not to "overdo" raising plant populations. In corn following soybean, we have seen yield responses into the mid-30,000s range, but increases usually are small beyond 32,000 or so.
- Selecting hybrids with good emergence and seedling vigor may be more important when planting early. Corn yields are generally affected much more by overall genetic potential than by the ability to emerge quickly, however. Getting a good stand is more important than getting the crop up quickly, though the two may be related, especially when planting is very early.
Based on research we have done, we can make a simple statement regarding early April planting of soybean in Illinois: Don't!--Emerson D. Nafziger