JANUARY WEATHER:			Soil Temperature (oF)
	Air Temp. (oF)	Humidity (%)	4" (Bare)	4" (Sod)
Monthly Average High	23.6	86.7	28.0	30.0
Monthly Average Low	5.5	54.8	25.2	28.2
Observed High (date)	42 (10)	100 (several)	36 (10)	37 (10)
Observed Low (date)	-23 (15,16)	28 (6)	16 (25)	23 (17,25,26)

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2009 Precipitation (in inches)

Month	Monthly Total	Monthly Departure from Average	Since January 1 Total Accumulation		Since January 1 Total Departure
January	0.27	-1.35	0.27		-1.35

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Corn Planting Date

The information farmers need can sure change from year to year. Before last year the main questions were, “How early can I plant corn?” and “Is there a yield advantage to planting corn earlier?”. This last year the question became, “How late can I plant corn?” Hopefully, the later question won’t arise this year, but these kind of questions are the impetus for much of the research conducted at NWRC. One such study has been the corn planting date and population study. This study has been conducted at the U of I research centers throughout the state under the guidance of Dr. Emerson Nafziger. The results shared in this newsletter are from the two most northern research centers located near DeKalb and Monmouth.

The hybrids planted in the planting date and population study were Pioneer 34B24 in 2005, 34B18 in 2006, and 34B20 in 2007 and 2008. The studies were planted at 44,000+ in 30 inch rows, and hand thinned at the V6 to V8 growth stage to the desired plant populations. The planting dates for the 4 years and 2 locations ranged from March 29 to April 11 for the first planting, April 18 to May 1 for the second, May 6 to 17 for the third, and May 27 to June 5 for the fourth planting. It should be noted that the first planting date (3/29) in 2005 at Monmouth was almost entirely killed by frosts on 5/2 & 3, so that data is not included in the yield averages. Included is the data from DeKalb with the same planting date, where the plants were hurt by the frost, but survived well enough to have adequate stands in almost all plots. These data are in actual plant populations and not seeding rates.

There was a significant effect of planting date by population on corn yield (Pr <0.0001, LSD 0.05 = 6.6 bushels per acre (bpa)) Figure 1. The yields of 1^st and 2^nd planting dates are not different at any of the population levels. At the 35,000 (35K) and 40K populations the yields dropped significantly between the 2^nd and 3^rd planting dates, but the decrease in yield was not as great with lower plant populations. The 4^th planting date yielded less than the 3^rd at all population levels.

Based on the yield response curve, the highest yield for planting date was April 15 for all populations, however, planting between April 5 and April 20 was within 2 bpa of the high. This means that the planting window for the highest yields these last 4 years has been between April 5-20. The drop-off in yield due to later planting is greater at the higher populations. Does this imply that higher populations should not be planted? No, it means that the higher populations have a higher yield potential, and that potential is more often realized with the earlier planting.

Does this mean that earlier is better? Only to a point; there is no additional yield benefit from planting earlier than April 15 and there are increased risks (e.g. Mar. 29, 2005 at NWRC). However, if the soil moisture is ideal and the soil temperature 50o and climbing, planting some corn the first week of April would not be a bad idea. If the conditions are less than ideal, there is no reason to push the planting date earlier than April 15, and the yield potential is still within 4 bpa of the highest when planting on April 25.

So what population should be planted? There have been a number of articles addressing corn populations in the ag press recently, and the recommendations shared there are very similar to what this data shows. When planted between April 5 and 20, the optimum plant population ranges between 33K and 36K plants per acre (Table 1). The optimum plant population depends on the cost of the seed and the price received for corn, and is defined as when the last seed purchased pays for itself with increased yield.. The optimum plant population decreased for the 3^rd planting date (May 6-17) to 3000 seeds per acre less shown in Table 1, and 6000 less for the 4^th planting date (data not shown). As yield potential decreases with later planting, fewer seeds are required to meet that potential. For example, the data in the graph show the yield at 30K, 35K, and 40K are all equal when planted on May 20. There is no need to plant extra seed when the yield will be the same. There could be the tendency to increase the population when the planting date starts getting late, as has been recommended with soybeans, but this data does not support that seeding increase.

A continuous corn study for 2 years at the same locations had very similar response to population and planting date. The hybrid planted was Pioneer 34A20.