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Concentration of CO2 in the Atmosphere

Rotating Crops for Sustainability

Bee visiting an alfalfa flower (Ivar Leidus, Wikimedia Commons)

Bee visiting an alfalfa flower (Ivar Leidus, Wikimedia Commons)

By George Harvey

The Union of Concerned Scientists has released a report on crop rotation, “Rotating Crops, Turning Profits” (UCS report). It is available as a pdf file at http://bit.ly/UCS-crop-rotation. It has a lot to say about the agricultural and environmental advantages of crop rotation methods not currently in widespread use. Specifically, it looks at growing non-GMO crops in 25 counties in Iowa.

Agricultural production in the Midwest is dominated by corn and soybeans. Together, they account for 70% of all crops. They are grown in a two-year rotation, in which land is devoted to each in alternating years. One result is that they get about the same amount of land from one year to the next.

There are a lot of problems with this approach to farming. One is that outside the growing season, which is only about five months per year, the land is bare. That fact, combined with the plowing that is done each year, creates erosion problems. Demands placed by corn on the soil are only partly met by nitrogen fixed by the soybeans, so the land is heavily fertilized, usually with chemicals. Pesticides are used to control weeds, insects, and fungi.

For seven months each year, the land is basically a desert, and during the other five months it is a desert that has been mono-cropped with corn or soybeans. With erosion and exposure of the land, the nitrogen compounds in the fertilizer escape into the air and water, as do the toxic pest controls. The problems arising from this had economic implications going into well over $100 million.

The UCS report gives results of studies into alternative systems of growing crops, comparing them with the standard two-year rotation. One of these is a three-year rotation, of corn, soybeans, and a crop combining clover with a small grain such as oats. The other is a rotation of corn, soybeans, alfalfa combined with a small grain combined, and then alfalfa alone. In both longer rotation systems, the second crop combined with small grain was plowed under to form “green manure.”

The results of the studies were impressive. The farm profits of both new rotation systems were slightly higher than those of the current two-year system. Herbicide use is reduced by 25% to 50% under the new systems, and this led to reductions of 81% to 96% in those toxins in runoff water. Synthetic fertilizers were reduced even more, by 88% to 92%, with organic fertilizer use also reduced, by 43% to 57%. The no-till system used instead of plowing produced a 91% reduction in soil erosion.

All of these improvements produce economic benefits to the farmers. They also produce economic benefits to the communities in nearby areas, especially those that are downstream from the farms, which have reduced problems with pollution.

Not all land can be advantageously farmed by the specific methods used in the study. The scientists doing the study indicated that about 20% to 40% of the farmland in Iowa could benefit from the changes. Other places can also benefit, however, as the identical practice can be used to a greater or lesser degree in all of the states of the Midwest, and similar systems can be used elsewhere.

One of the most important aspects of this, however, is not included in the UCS report. It is the overarching question of how soil can be used and treated more thoughtfully. It happens that a discussion draft of a different, broader report, “reThink Soil: a Roadmap for U. S. Soil Health,” was released late last year by The Nature Conservancy. That report is available as a pdf file at http://bit.ly/TNC-rethink-soil.

Taken together, the broader message of these two reports is clear. It applies not only to Iowa or the Midwest, but to all farmland. We need to treat all soil with respect and understanding for our own sakes. The central issue is clearly stated in the executive summary of “reThink Soil”. It says, “Healthy soil is the cornerstone of life on earth.”

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