If the current USDA estimate holds, the 2005 corn production season for Wisconsin will be the best on record. USDA – Statistics Service estimates that the average corn yield in Wisconsin is 150 bu/A representing a 4.9% increase over the previous record (Figure 1). The previous Wisconsin record was set in 1999 at 143 bu/A. Since 1975, corn yields have increased an average of 1.7 bu/A yr.

With the exceptions of Chippewa Falls and Spooner, nearly every location had 2005 corn grain yields greater than the average yield of the previous 10 years (Table 1). Grain yield increases of more than 25% were measured at Lancaster, Galesville, Hancock, and Rhinelander. At Hancock, the average of 149 hybrids was 255 bu/A. A new trial average record and hybrid performance record was measured at Hancock for the UW Hybrid Trial program (Table 2).

Many people are asking what happened during 2005 to produce record yields. Are corn hybrids that much better? Was it the weather? If one were to list the top reasons for the 2005 crop, weather might not be the primary reason for the outstanding yields. Improved hybrid genetics is often suggested. Better management might also be important.

Lets take a closer look at other record yielding years in Wisconsin. In 1994, grain yield increased 20 bu/A over the previous record year representing a 18.4% jump, the greatest increase ever recorded. Only three other times in Wisconsin's history has corn yields increased at comparable rates. In 1949, corn yields were 55.4 bu/A, and represented a 15.4 percent jump over the previous record year of 1948 when yields were recorded at 48 bu/A. In 1952, corn yield increased 15.5% over the previous record year of 1949. During 1966, corn yields were 88 bu/A, an increase of 15.8 % over the previous record year of 1965. It might be helpful to review the weather during these record years of 1949, 1952, 1966, and 1994.

Table 1. Summary of the 2005 UW corn hybrid performance trials for grain yield (bu/A) conducted at twelve locations in Wisconsin. ( N= number of hybrids tested.)
	1995-2004		2005		Percent
Location	N	Yield	N	Yield	change
Arlington	1838	198	167	227	15
Janesville	1837	198	167	217	10
Lancaster	1837	189	166	238	26
Fond du Lac	1637	171	149	207	21
Galesville	1634	178	149	238	34
Hancock	1633	197	149	255	29
Chippewa Falls	1528	149	142	130	-13
Marshfield	1362	158	142	180	14
Seymour	1204	161	142	169	5
Valders	1530	153	142	184	20
Spooner	1661	142	94	132	-7
White Lake/Rhinelander	511	106	47	187	76

Weather patterns

In 1949, conditions were favorable during most of the growing season. The month of April was drier and warmer than normal with abundant sunshine and no extremes in temperature. Abnormally high temperatures were observed early in May and unseasonably cold temperatures were seen the last week in May. Planting was ahead of schedule and crops made good progress, but were slowed somewhat by cold temperatures and soil moisture deficits at the end of May. Dry weather during the later part of May and the first two weeks of June was offset by good rains during the second half of June and first part of July which replenished soil moisture. Early planted corn ranged from knee-high to waist high by the end of June. The first killing frost was on the September 29. Warm, dry weather during the fall was ideal for maturation and harvest.

1952 was considerably warmer and drier than normal. In April, the first half of the month was cold, cloudy and damp, while the second half was abnormally warm, sunny and dry. Planting began earlier with some corn planted by the end of April. Temperatures averaged near normal in May although the first few days were abnormally warm and the precipitation was below normal. By the end of May, about 70% of the intended corn acreage was planted. June was warmer and wetter than normal. Most cornfields were better than knee high by the end of June. On October 3, there was a killing frost. October was one of the coldest and driest on record.

During 1966, after a wet fall the previous year, March was warm and wet. During April temperatures were slightly below normal, precipitation was normal, and it snowed in late April. In May, subsoil moisture was adequate, temperatures were still slightly below normal. June temperatures were a little above normal, moisture deficiencies were reported, and corn was at normal developmental stages. July had above normal temperatures and below normal rainfall. Needed rainfall occurred during August and corn kept growing. September was dry with normal temperatures. October and November was ideal for harvesting with above normal temperatures and below normal precipitation.

In 1994, planting conditions were excellent. Adequate spring soil moisture was reported over most of the state. Farmers were able to plant earlier than normal with few delays. By May 15, corn was planted on 65 percent of the acreage, which compared to only 19 percent in 1993 and 46 percent for the five-year average. By May 30, about 97 percent of the corn was planted, compared to 75 percent the previous year and 85 percent for the five-year average. Little rainfall was recorded during May with some parts of the state experiencing moisture deficiencies by mid-June. Timely rains and above average heat units allowed faster growth than normal and by July 24 corn was 75 inches high and 47 percent silked compared to the five-year average of 57 inches high and 21 percent silked. Harvest conditions were ideal with killing frosts in October.

Common characteristics of these record years include: 1) earlier than normal planting, 2) adequate to dry spring soil moisture, 2) mild moisture stress during vegetative corn development with soil moisture eventually replenished to normal levels, 3) corn development was typically ahead of normal at some point during the growing season, 4) fall killing frosts were at the end of September or during October, and 5) fall harvest conditions were typically dry. In the record years of 1949, 1952, 1966, and 1994, inadequate soil moisture supplies were reported during late May and early June. Mild moisture stress, during early corn development, increases the allocation of photosynthate to roots at the expense of shoots and leaves, thus, promoting deeper root growth and increased soil exploration for water, minerals and other nutrients. As moisture stress becomes more severe, total root weight can decrease. In all of these years, rainfall replenished soil moisture supplies to normal or above normal levels by late June to early July.

In 2005, early planting dates and dry conditions were prevalent throughout the state. Drought stress also occurred. This year drought was present until pollination and timely rains allowed fertilization to take place and kernels to develop normally. Harvest conditions were ideal.

The Yield March Continues …

The corn grain yield march continues as evident from numerous sources. Since 1975, grain yield in Wisconsin has been increasing at the rate of 1.7 bu/A according to the USDA (Figure 1). In the UW hybrid trials, corn grain yields of all hybrids in the trials have been increasing at the rate of 2.0 bu/A yr since 1973 (Figure 2). The top-yielding hybrid in the program has been increasing in yield at the rate of 2.6 bu/A yr.

At Arlington, the rate of grain yield increase since 1973 has been 2.5 bu/A yr (Figure 2 and Table 2). The rate of grain yield increase at a location ranges between 1.1 and 2.8 bu/A yr (Table 2). Chippewa Falls has the smallest rate of increase, while Lancaster has the greatest rate. The Seymour and Valders locations have not had a significant trendline over time. The record location trial average of all hybrids tested for a production season ranges from 174 to 255 bu/A with 8 of 11 locations setting records since 2002. The highest yielding hybrid, Dairyland Stealth 5204, was measured at Hancock in 2005 and produced 288 bu/A.

Table 2. Rate of grain yield increase at a location, record year at a location, and top hybrid performance at a location in the UW corn trials (1973 to 2005).
Location	Rate of Yield Increase	Record Year at a Location			Top Performance at a Location
Location	Rate of Yield Increase	Year	Hybrids	Average	Year	Brand Hybrid	Yield
	Bu/ A yr		Number	Bu/A			Bu/A
Arlington	2.5	1998	169	248	1998	Jung 2668	284
Chippewa Falls	1.1	2004	145	174	1994	Lemke SL35	225
Fond du Lac	2.3	2005	149	207	1994	Golden Harvest H2387	252
Galesville	2.6	2005	149	238	2005	Pioneer 35A30	285
Hancock	2.5	2005	149	255	2005	Dairyland Stealth 5204	288
Janesville	2.6	2004	173	237	1999	Renk RK835	267
Lancaster	2.8	2004	173	242	2004	Croplan Genetics 691BtLL	282
Marshfield	2.4	2002	150	199	2002	Dahlman D4515	223
Seymour	--	2003	137	202	2003	NK Brand N32-L9	231
Spooner	2.2	1999	189	168	2001	Pioneer 37R71	229
Valders	--	1999	168	199	1999	Dairyland Stealth 1280	239

Another source of evidence that the corn grain yield march is continuing can be found in Wisconsin corn grower contests. These contests require 10 acre fields of which 1.25 acres is harvested and measured. Figure 3 shows the rate of increase for various divisions of the UW Profits through Efficient Production Systems (PEPS) program and National Corn Growers Association (NCGA) yield contest. Using the top-producer from each division each year, the rate of corn grain yield increase was 3.0 bu/A yr across all contests (Figure 3). The NCGA No Till/Strip Till Irrigated division has increased 1.9 bu/A yr, while the PEPS Livestock corn division has increased 5.2 bu/A yr. The highest recorded yield for Wisconsin was 296 bu/A, and was measured in an NCGA contest plot in Grant County during 2004.

Clearly, the corn yield march continues. The rate of progress in Wisconsin lies somewhere between 1.1 to 5.2 bu/A yr. The development of transgenic hybrids will likely continue the yield march through increased crop protection and continued improved genetics. Some of the genetic and management reasons for the continued yield march in corn include: resistance to root and stalk lodging (necessary for machine harvesting at higher plant densities), resistance to diseases (little data to support), resistance to insects, improvement of stay-green, continuous improvement of second generation European Corn Borer resistance, use of single-cross hybrids, resistance to barrenness, better pollen production, production under higher population, earlier planting date, better seed quality, improved cold tolerance, better germination and emergence, use of commercial fertilizers, better pest control techniques.