FEBRUARY WEATHER:			Soil Temperature (oF)
	Air Temp. (oF)	Humidity (%)	4" (Bare)	4" (Sod)
Monthly Average High	38.6	90.6	32.5	31.5
Monthly Average Low	18.6	48.6	29.0	29.9
Observed High (date)	64 (8)	100 (several)	42 (11)	34 (19)
Observed Low (date)	-23 (15,16)	28 (6)	16 (5)	23 (5)

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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
February	2.43	+0.71	2.70		-0.64

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Continuous Corn: What Does It Need?

There have been several aspects of continuous corn management studied at NWRC the last several years. While it is assumed that continuous corn needs to be managed differently than rotated corn, what needs to be different? Hopefully, summaries of the following studies can offer some light on the subject.

One continuous corn study involved tillage, fertility, and population. From 2003-07, the fall tillage comparison was between conventional (chisel plow) and a modified moldboard plow. The fertility included a normal level of 220 lb N with recommended P and K based on soil tests, and a high level with an additional 100 lb N (70 applied sidedress at V12-14), 80 lb P and 150 lb K. The two plant populations were 32,000 and 40,000 plants/acre. Hybrids with rootworm Bt (RwBt) were planted in 2006 and 2007.

Table 1: Continuous Corn Management, Monmouth, 2003-07

		32,000 Plt Pop	40,000 Plt Pop
Tillage	Fertility	Yield (bpa)
Conv.	220 lb N	175	159
	320 lb N + PK	181	176
Mod. Plow	220 lb N	186	182
	320 lb N + PK	192	189

The modified moldboard did increase the yield of continuous corn 14 bushels per acre (bpa) compared to the chisel plow (Table 1). Residue counts after planting averaged 59% with the chisel and 35% with the modified moldboard. Getting some of the residue off the soil surface appears to have helped the yield.

The higher level of fertility increased the yield 9 bpa over the normal fertility, although the increase would need to be more than 45 bpa to pay for the additional fertilizer bill.

The higher population actually decreased yield 7 bpa. This suggests that ultra-high plant populations do not guarantee higher yield, and in this case they did not handle the stress as well.

This study was modified in 2008, changing the tillage to include fall strip-till instead of the modified moldboard. Fungicide application at tasseling replaced the population factor. The two fertility levels stayed the same. Data are 2008 averages from four U of I research centers, DeKalb, Monmouth, Orr Center, and Urbana. Hybrids with RwBt were used at all centers.

Table 2: Continuous Corn Management, DeKalb, Monmouth, Orr Center, Urbana, 2008

		No Fungicide	With Fungicide
Tillage	Fertility	Yield (bpa)
Conv.	220 lb N	199	207
	320 lb N + PK	213	220
Strip-Till	220 lb N	205	215
	320 lb N + PK	214	223

Strip-till yielded an average of 4 bpa better than conventional tillage with a chisel plow (Table 2). The high level of fertility added 11 bpa, but again not enough to pay for the extra fertilizer. The fungicide treatment increased yield 9 bpa across all locations. At Monmouth, the residue counts diagonally across the field after planting were 72% in the conventional tillage and 86% in the strip-till.

A second study compared the effect of tillage and residue removal on the yield of continuous corn. The two tillages compared were conventional with fall chisel plowing and no-till. The no-till had no tillage other than the coulters of the liquid N application at 3 to 4 inches deep. Residue removal treatments after harvest included 1: All- residue removal(chopping with a batwing mower, raking and baling the stalks), 2: 1/2 residue removal (raking and baling the stalks), and 3: no residue removal. Nitrogen rates had been knifed into plots prior to planting (data not included).

Table 3. Corn Residue Removal, Monmouth, 2007-08.

	Corn Residue Removal Level
	All	1/2	None
Tillage	Yield (bpa)
Conv.	253	252	254
No-till	247	242	226
LSD 0.10 = 22 bpa

There were no differences between corn yields at any of the residue levels with conventional tillage (Table 3). With no-till, the yield with no residue removed was significantly lower than all the other treatments, while those with all or 1/2 of the residue removed were not different from the yields in conventionally tilled soil. The residue levels at planting in 2008 were 18, 23, and 68% respectively for all, 1/2 and no residue removed before conventional tillage. In no-till, the residue cover was 48, 53, and 93%, respectively, all, 1/2, and no residue removal.

In a crop rotation study, non-RwBt hybrids were planted 2002-05 and RwBt 2006-08. In continuous corn the non-RwBt averaged 99 bpa and the RwBt averaged 197 bpa. For comparison, the corn/soybean rotation non-RwBt averaged 177 bpa and RwBt 208 bpa.. While there were environmental differences in the comparison of hybrids, (e.g. amount of rain in different years) the yield differences were much greater between the hybrids for the continuous corn than the rotated. It has been observed that the continuous corn yields across NWRC have been more consistent and closer to the yield of rotated corn since the introduction of RwBt hybrids.

Following are a few observations that can be made from these results.

1. Some reduction in the amount of residue left after the previous corn crop can make a difference in the corn yield. Burying the residue with tillage, pushing the residue off the row with a strip-till tool, or removing the residue seem to all be effective in increasing continuous corn yield.
2. The deeper, more thorough tillage generally increased yield (Tables 1 & 3), but the tillage and removing of the residue over the row with a strip-till tool resulted in better yields than chisel plowing (Table 2).
3. Increased fertility can increase yield in continuous corn, but will not totally compensate for increased residue cover. Additionally, the yield response is not great enough to justify excessively high rates for fertilizer. Following the guidelines in the Agronomy Handbook and the N Rate Calculator (http://extension.agron.iastate.edu/soilfertility/nRate.aspx?mode=advanced) will help growers stay close the optimum fertility levels (Tables 1 &2).
4. Increasing continuous corn yields is not just a matter of needing more plants above the rates typically planted in rotated corn (Table 2)(Jan 09 newsletter).
5. Lastly, choosing the right hybrid is more critical for continuous corn as the environment it is grown in is less forgiving than rotated corn.