Three or four year crop rotation vs corn/soybean rotation
They conducted their study at the Marsden Farm and used a randomized block design to be able to compare the results of the three cropping systems. The 3-year and 4-year systems added the production of a small grain (triticale and oat) along with the use of a legume and composted animal manure. Small amounts of synthetic fertilizer and herbicides were used in the 3-year and 4-year rotations while the 2-year rotation used conventional amounts of these products.
The first finding that they discussed in their report was that the diversified rotations were just as profitable as the standard corn/soybean rotation that is being used by most farmers in Iowa and throughout the US Midwest. The profitability was measured without accounting for costs of land, management time, and federal subsidies.
The researchers found that “weeds were managed effectively in all three cropping systems in both the ‘startup’ and ‘established’ phases, in spite of reducing herbicide use by 88 percent in the 3-year and 4-year rotations compared to the 2-year rotation.”
The use of labor in the 3-year and 4-year rotations was greater than in the 2-year rotation, but the cost of this was compensated by lower use of synthetic nitrogen inputs and reduced herbicide inputs.
“Weeds were suppressed as effectively in [the 3-year and 4-year] systems as in the 2-year rotation, with declining soil seedbanks and negligible weed biomass, yet herbicide inputs in the 3-year and 4-year rotation plots were 6 to 10 times lower, and freshwater toxicity 200 times lower, than in the 2-year rotation.”
The authors discussed their findings writing, “Reintegration of crop and livestock production, as represented by the forage legumes and manure applications present in the more diverse systems, is not simply another aspect of cropping system diversification. Instead, it embodies an important principle in sustainable agriculture: system boundaries should be drawn to minimize externalities. Animal manure is produced regardless of whether feed grains are shipped to centralized concentrated animal feeding operations, or produced within integrated crop-livestock farming operations. In the former case, the manure may become a waste product and water pollutant if quantities exceed available land area for field application, whereas in the latter case, it contributes directly to crop nutrient requirements, improves soil quality, and reduces fossil fuel subsidies associated with grain transport and external N fertilizer inputs.