Issue No. 6, Article 14/May 5, 2006
Planting Issues: Looking Back and Looking Ahead
Planting of the Illinois corn crop was 72% complete as of April 30. Because we have had early planting the past two years, that percentage seems low to some people, but it really isn't. The five-year average for that date is only 59% planted, and that average includes the 80% or so that was planted by this date in both 2004 and 2005. While there was rainfall over much of the state during the past week that will delay the end of corn planting, we expect corn planting to be recorded as "timely" for 2006. Soybean planting was at only 5% by April 30, which is the average for the past five years.
April growing degree-days (GDDs) were above average this year, with about 300 at Urbana compared to the average of 230 or so. GDDs were also reasonably well distributed, so corn planted any time during the month tended to get the 110 to 120 GDDs needed to emerge within 10 to 15 days. With good planting conditions and relatively warm soils, emergence is uniform and at a high percentage in most fields so far. Where heavy rain fell during the past week, ponding could be an issue in localized areas. But because the drying conditions have been moderate, we don't expect soil crusting to be a serious problem. No planting season is ideal, but this one has been as good as any in recent years.
With good emergence conditions so far, we don't expect unusual problems with uneven emergence this year. That was not the case last year, when soils turned wet and cold for the last 10 days of April, followed by frost injury that caused uneven plant damage and uneven plant growth. We think that these two things--uneven emergence and uneven growth after emergence--have similar effects on the crop. Both result in uneven competition between neighboring plants. When that happens, larger, more competitive plants tend to produce more yield than they otherwise would, but this amount of extra yield is usually less than the yield loss suffered by the smaller plants, so the net effect is lower yield. How much yield is lost depends on the relative size difference and seasonal growing conditions, but we think that a difference of 2 leaf stages by about the 6-leaf stage in corn will likely result in some yield loss due to unevenness.
We do not know if soybean suffers from unevenness in plant size to the same extent that corn does. Because plant loss in soybean tends to increase when plant populations increase above 125,000 per acre or so, it's likely that some of the later-emerging plants may just be the first to die out. With 100,000 plants usually enough to maximize yield, the presence of later-emerging plants in higher populations may make little difference, since they will usually produce little and also will not compete very much with larger, earlier-emerging plants.
I covered issues regarding soybean planting in an earlier issue and will not repeat all of those here. It is worth noting, however, that we are not yet into the period when soybean yield is lost with planting delays, so there is no benefit of planting soybean seed into soils that are too wet, especially if there are any questions about seed quality. Fungicidal seed treatments will be helpful if soils are likely to get wet soon after planting. With soil temperatures generally favorable, and with the weather outlook indicating that they will likely stay this way, planting should be kept to no deeper than 1-3/4 inches, and planting only 1-1/4 inches deep is probably deep enough in many soils.
We are moving into the period when we expect yield losses with further planting delays in corn. Be careful not to work or plant soils when they are too wet, since this can easily cause more yield loss than would a planting delay of several days needed to allow soils to dry adequately. As soil temperatures continue to increase, there is little need to plant corn seed more than 1-1/2 inches deep. Don't change the planting rate for corn based on the slight delay in planting up to now; plant the same population you would have a week or two ago.--Emerson Nafziger