Within the last farm generation (20 to 30 years) significantly more acreage has been planted to corn and soybean in Wisconsin and the Midwest U.S. This cropping system is a relative "new kid on the block." Much discussion is taking place about whether or not the corn-soybean system can be sustainable. This article is the first in a series to evaluate crop rotations in Wisconsin. The objective of this article is to discuss the historical changes that have occurred in Wisconsin cropping systems.

Crop rotation is a management system of growing one or more crops in sequence on the same piece of land, the sequence being repeated again and again (Cady, 1991). Rotations can be as simple as monocultures year after year or complex involving grain crops, forage grasses and legumes, and livestock (Hoeft et al., 2000) .

The major crops produced in Wisconsin have traditionally supported the dairy and livestock industries. Corn grown for grain and silage has been an important crop since 1865 (Figure 1). Wheat was produced on the greatest number of acres between 1865 and the early 1900s after which many farmers were switching to barley and oats. Oat was produced on a large proportion of acres until tractors came into widespread use in the 1940's. The addition of soybean to Wisconsin agriculture is relatively recent. It wasn't until the late 1970's that soybean acreage approached 300,000 acres. By 1997 soybean was produced on 1 million acres.

It is difficult to get a handle on how fast crop sequences are rotated through time. One approach to measuring how fast crops are rotated is to add the acreages of crops together and calculate the proportion of acres relative to the total cropland available. If two crops are grown on more than 90% of the cropland available, then the rotation sequence is limited to those crops with some acres in continuous monoculture production, most of the acreage rotated between the two crops, and the balance to miscellaneous crops. When the total proportion of two crops is >85% of the total cropland, nearly all of the land is used for production of those two crops and little crop diversification exists.

In 1972 only Piatt County in central Illinois had 75-85% of its total cropland in corn and soybean (Figure 2). By 1998, many counties in the Midwest U.S. have 75-85% of the total cropland in corn and soybean. A total of 26 counties have more than 85% cropland in corn and soybean.

The first county in Wisconsin to have more than 85% of its cropland in corn and soybean was Rock County during 2001 (derived from USDA Statistics).
The southern two tiers of counties in Wisconsin have traditionally had a large proportion of acres in corn and soybean, and recently more acres are increasing towards the northeast.

Clearly the crop sequence landscape has changed dramatically from a generation ago. Certainly years like the winter of 2000-2001 when natural gas prices rose to record levels, nitrogen fertilizer was in great demand and prospects loomed for growing soybean in the same fields for two (really three) years forced many growers to reevaluate their crop rotations. This situation may or may not be sustainable, but greater risk to the farmer may be a consequence of these rotations and needs to be considered for crop management. Next week's article will be on "What have we learned about crop rotation?"

Literature Cited

Cady, F. B. 1991. Experimental design and data management of rotation experiments. Agronomy Journal 83:50-56.

Hoeft, R. G., Nafziger, E. D., Johnson, R. R., and Aldrich, S. R. 2000. Modern corn and soybean production. First edition. MCSP Publications. Champaign, IL.

Figure 1. Harvested Acreage of Crops in Wisconsin (1866-2001)

Text Box: Figure 2. Percent of land in corn and soybean during 1972 and 1998 (source Porter, 2000).