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Diversify Crop Rotations

1 Spoke WheelThe first spoke is crop rotation diversity. Crop rotation is the 'repetitive growing of an ordered succession of crops on the same land over multiple years.' The first reason diverse crop rotations are important is that yields improve. Research from a long-term crop rotation trial in central Pennsylvania showed that, compared with continuous corn, corn yields were improved 7 percent when grown in rotation with soybeans, 15 percent in the first year after alfalfa/grass hay and 16 percent in a corn-oat-wheat-red clover hay rotation (Figure below). Interestingly, yield improvement of com after alfalfa/ grass hay was still present four years after termination of the hay.Figure 10 with bar labels and caption

The rotation effect on crop yield is well established agronomically (though not well understood) and confirmed in many different trials. Yet, it seems to be neglected. Why? It may be that agricultural systems have become focused on one or two crops due to high infrastructure and machinery costs. But, perhaps it is time to rethink this approach. Here are a few reasons why more diverse crop rotations are more beneficial:

Legumes in rotations fix atmospheric nitrogen through their symbiotic relationship with rhizobium bacteria and reduce the need for nitrogen fertilizer in the rotation. Part of the legume nitrogen can be counted as a credit towards the next, non-leguminous crop. Some legumes, such as peas, have been observed to have a very beneficial effect on following grass-type crops while terminated alfalfa sod supplies almost all the nitrogen required for a following com crop.

Crop rotation is an important pest management tool. For example, corn rootworm is not an issue if corn is rotated with other crops. Weeds are also easier to control in a diverse crop rotation because of a range of practices to control them, such as narrow and wide row crops, winter and summer annuals, biennials and perennials, fertilizer placement (versus broadcast applications), different herbicide programs and application timings in the different crops, mowing, grazing, and harvesting at different times of the year. All these practices together work to reduce weed populations. By using diverse crop rotations in continuous Soil Agg Stability with captionno-till, herbicide use was reduced 50 percent compared with simple crop rotations on farms in the Great Plains.

Soil health is improved. Greater crop diversity above ground will also result in a more varied microbe food source and diverse microbial community below ground. Crops rotated with different root architectures, will impact soil structure in a variety of ways. Using massive, fibrous root systems will help improve aggregation, especially near the surface. The deep taproots of certain perennials can penetrate up to ten-feet deep. Old root channels will be available for subsequent crops, allowing for deep rooting and water percolation. In a long-term crop rotation trial in central Pennsylvania, aggregate stability was higher the more diverse the crop rotation (Figure at left).

Machinery is used more efficiently. In simple rotations or monocultures, equipment is used only a few months in the year. With a diversity of crops that are planted and harvested at different times of the year, the combine, planter, and drill can be used more months of the year. It is also possible to use smaller, more affordable equipment.

There are fewer labor peaks. Labor needs are spread out over the year. Therefore, more diverse crop rotations also increase employment opportunities in rural areas.