Extend your crop rotation
Corn and soybeans certainly work well for Iowa farmers, but extending the crop rotation to include small grains and forage can improve the sustainability of row crops by reducing costs and increasing yields. Extended rotations help manage risk by improving weed and pest control, breaking disease cycles, and spreading out a farmers’ workload throughout the growing season. Over time, enhanced soil quality supports better fertility management and builds resilience against drought and volatile weather.
Iowa farmers have a number of small grains to choose from, including oats, wheat, cereal rye, barley, triticale and succotash, a mixture of small grains. Wheat and oats are the two most typically grown on Iowa farms, but production of cereal rye is increasing as more farmers grow cover crop seed for sale or use on the farm.
Including a perennial forage crop like alfalfa or mixed hay brings additional benefits if you have animals to feed or a market for hay. If not, a less-expensive underseeding, such as red clover, can be grown as a plow-down or green manure.
• Extending crop rotations to include small grains and forages has many benefits.
• Adding diversity improves sustainability of row crop-based systems.
• Higher diversity in the system can lead to higher yields with fewer inputs.
Spreading risk and workload
The planting and harvest schedule for small grains and forages is offset with the fieldwork for corn and soybeans. Scott Shriver, Greene County, grows a small grain, usually wheat, in a five-year rotation with corn and beans. “It gives us a different time of year that we are doing things to the ground,” he says. “We can get some cropland planted before the time is right for corn and beans.”
A diversified rotation spreads out the workload, he notes. “The small grains come off in middle-to-late July, so there are some things you can do because you have that early fall for portions of the farm.” This frees up time for planting a cover crop, additional weed management, or maintenance of terraces and grassed waterways. The fall harvest is a lot less hectic when a portion of the grain is already harvested.
The earlier planting helps with effective weed control; summer annual weeds may fail to germinate under the canopy of early seeded small grains. Weeds that do persist get cut when the crop is harvested, before the weeds set seed. Shriver’s operation is certified organic, and crop rotation and crop diversity is one of the critical weed management tools in organic production.
For conventional row crop farms, increasing the diversity of crop types allows growers to diversify their herbicide programs and select chemistries with different modes of action over the course of several years. This typically leads to better weed control and minimizes the risk of fostering herbicide-resistant weeds. Most farmers will find they don’t need any herbicides for the years of small-grain production.
Shriver finds his rotation to be effective for disease management, particularly for pathogens that overwinter in soil or residues. By growing a crop that is not a host for a given pathogen, the pathogen can’t reproduce. Inoculum levels in the soil decline, and there is reduced pressure the next time the pathogen’s host crop is grown. Soybean cyst nematode, for example, causes the greatest yield loss of any pathogen on soybeans in Iowa. Research shows SCN populations can be halved when soybeans are rotated with corn and wheat.
Extended crop rotations also control insect pests that overwinter in soil or residue as eggs or larvae. Many pests lay their eggs in cornfields in late summer or early fall. If corn is planted the following year, the larvae emerge ready to devastate the crop.
Initially, a simple two-year rotation with soybeans was enough to disrupt this cycle of corn pests. More recently some cutworms have found a workaround by laying their eggs in soybean stubble in anticipation of the corn crop that will follow. Other pests, like corn rootworms, have developed a two-year life cycle to last over the duration of corn-soybean rotation. However, extending a rotation to three or more years by including a small grain or forage crop is enough to disrupt the life cycles for both of these costly pests.
Higher yields, fewer inputs
Fewer weeds, insects and pathogens lead to fewer costly inputs to keep them at bay. The savings will be different for each farm depending on management, the land’s history and pest pressures. It may take several cycles through the rotation for all the benefits to come to fruition.
More assuredly, supporting nutrient availability through crop rotation can pay off in the short term. When the added crop is a legume, farmers can “grow their own nitrogen.” In an eight-year crop rotation study (two times through a four-year rotation), researchers at Iowa State led by Matt Liebman found a four-year rotation of corn-soybeans-oats/alfalfa-alfalfa achieved higher corn and soybean yields (4% and 9% increases for corn and soybeans, respectively) using 86% less synthetic nitrogen. The Iowa Nutrient Reduction Strategy examined a five-year crop rotation with corn, soybeans and three years of alfalfa and found 7% increases in corn yield.
Not only do extended rotations use less fertilizer, but also improvements in soil health mean soils are better able to hold on to the fertilizers that are applied. Remarkably, extended crop rotation is the only management practice in the Iowa Nutrient Reduction Strategy that could nearly achieve Iowa’s nitrate reduction goals alone, with studies showing an average 42% reduction in nitrate-N losses — without taking land out of crop production and yet increasing corn yields.
Larsen is communications and policy associate with Practical Farmers of Iowa.
This article published in the June, 2014 edition of WALLACES FARMER.
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