Leopold Center - Four-year rotations offer promise at bottom line

As energy prices go up, the Leopold Center continues to monitor the bottom line as it relates to alternative cropping systems that would require more management but fewer purchased inputs. And the bottom line is looking good for four-year systems.

Since 2002, Iowa State University agronomist Matt Liebman has been conducting a crop rotation experiment at the Marsden Farm near Ames in Boone County. He is investigating the effects of different crop management systems on weeds, but also collects yield data that can be used to determine the economic performance of different systems over the past three cropping seasons.

The study includes three rotations:

Averaged over the three-year period of 2003-2005, Liebman reduced nitrogen fertilizer use by 50 and 73 percent in the three- and four-year rotations, and reduced herbicide use by 71 and 78 percent, while averaging yields slightly higher than the two-year rotation.

"Despite those reductions in fertilizers and herbicides, we were able to maintain fertility levels and achieve excellent weed control," Liebman said.

The three- and four-year rotations rely on rotary hoeing, banded herbicide and interrow cultivation for weed control during the corn-soybean portion of the rotation; the two-year rotation uses broadcast pre- and post-emergent applications. The longer rotations exploit nitrogen fixation by alfalfa and clover, and receive cattle manure (seven tons per acre) prior to corn.

Despite differences in fertilizer and herbicide inputs, corn and soybean yields have averaged slightly higher than the two-year rotation. Triticale yields in the three-year rotation (with a red clover companion crop) and the four-year rotation (with an alfalfa companion crop) have been similar.

Returns to land and management were greatest in the four-year system ($176 per acre), least in the three-year system ($144 per acre) with the two-year system falling in between ($158 per acre).

Labor requirements were 58 percent and 81 percent higher in the three-year and four-year rotations, respectively, compared with the two-year system. Compared with the two-year rotation, production costs in the three-year and four-year rotations were 23 percent and 28 percent lower.

A chart with an economic comparison of the three crop rotation systems was prepared by ISU Extension farm management field specialist Craig Chase. Fieldwork hours and cost of production are estimated using annual figures published by ISU Extension. Corn and soybean prices were 10-year NASS averages, triticale price was set the same as the corn price, and alfalfa and straw prices were those commonly found in Iowa over the past few years.

The research, which is continuing in 2006, is funded by a multi-year grant from the Leopold Center Ecology Initiative, the ISU Agronomy Department Endowment, and the USDA National Research Initiative.