Wheat/Red Clover Intercropping Explored

By Jane Fyksen, Crops Editor
Thursday, March 20, 2008 4:06 PM CDT

Historic wheat prices last fall sparked increased planting of winter wheat in Wisconsin. Since then, wheat has rocketed even higher, fueling producer interest in spring wheat, too.

Farmers choosing to grow wheat should consider interseeding red clover for a number of reasons. “Red clover can supply nitrogen to a subsequent corn crop, provide forage for livestock and build soil quality,” reports Iowa State University associate professor of agronomy Lance Gibson, who highlights Upper Midwest research showing average fertilizer replacement value of red clover for a subsequent crop of corn to be 80 to 120 pounds per acre. Animal performance with red clover can be as high as alfalfa. And red clover can suppress weeds, build soil organic matter and prevent erosion.

Interseeding red clover into winter wheat is accomplished by frost seeding. Red clover is broadcast over the wheat crop in late March or early April in Iowa and southern Wisconsin (so freezing-thawing action can drive seed into the soil) and slightly later in the northern portion of the state.

For spring wheat acres, red clover can be seeded with the wheat. Combined planting requires a seed drill capable of simultaneously handling both wheat and red clover seed.

Iowa State University and USDA’s National Soil Tilth Lab have examined intercropping winter wheat with red clover and proclaim it “a promising option” for producers wanting to expand the usual corn/soybean rotation. Adding the winter cereal grain is a hedge against weather extremes, disease and insect outbreaks and high production costs. It better distributes labor and equipment, improves cash flow and provides additional income from straw. Red clover n as a soil-building green manure n can significantly cut N fertilizer needs and provide up to four years of high-value forage.

This system is good for the environment, according to Gibson, who’s looked at it with Jeremy Singer, USDA research agronomist, Stephen Barnhart, Iowa State University agronomist, and Brock Blaser, also in the ISU agronomy department. Winter wheat/red clover intercrops protect soil, as it’s only vulnerable to erosion for a short period during cereal establishment. Winter wheat accumulates excess nutrients not used by the previous crop and uses soil water that could otherwise contribute to nitrate leaching. Planting winter wheat after soybeans requires little to no tillage, which preserves soil organic matter. What’s more, winter wheat rarely needs herbicide for weed control. And winter wheat with a legume intercrop can increase soil carbon, leading to increased soil organic matter and better soil structure.

Winter wheat and red clover are excellent crops for suppressing persistent, soil-borne pests of corn and beans. Research has documented that red cover suppresses corn rootworm, soybean cyst nematode and weeds. Minnesota work, in fact, shows red clover to be better at suppressing SCN than corn even. And Iowa research found a three-fold reduction in weed density for red clover intercropped into winter wheat compared to fallow after winter grain alone.

A well-drained field without soil compaction is best for winter wheat. Soybeans are a good previous crop, because they’re harvested early enough for timely planting of wheat, and soybeans supply a good seedbed for no-till seeding, not to mention supplying residual N to the winter cereal grain. ISU research has found that wheat yield can be up to 25 percent lower when corn silage is the previous crop compared to soybeans.

Be sure there are no herbicide residues that’ll injure either the wheat or red clover. Adjust the combine to spread residue evenly while harvesting the prior crop; that’ll help with wheat planting.

Phosphorus, potassium and lime should be applied prior to planting. To maximize production, ISU recommends topdressing with 30 pounds of N per acre early spring when the wheat begins to green up. Delaying N until jointing (stem elongation) or later has little impact on yield. And this intercropping research team warns that excessive N fertility can be as much of a problem as under fertilizing, as it leads to lodging, which in turn, results in the crop maturing unevenly, harvest losses and smothering of red clover seedlings. Manure should be applied sparingly before or after the winter wheat.

Optimum seeding rate is 30 seeds per square foot (or roughly 100 pounds per acre) early in the winter wheat planting season and 40 seeds per square feet later. Using rates that optimize grain yield don’t significantly reduce red clover establishment or productivity.

No-till is a good strategy. Drill in rows spaced 8 inches apart or less and at a depth of 1 to 1.5 inches. As noted, weeds and insects aren’t typically a problem. Fusarium (scab), septoria and rusts are ones to worry about, but only once every five years or so. Grain with scab looks chalky. It can cause problems when fed to livestock, especially pigs, and should be tested for mycotoxins. Non-breeding cattle and poultry tolerate scab-infested grain well.

Winter wheat should be cut at 6 to 8 inches in height to avoid excess removal of red clover stems and leaves. This will allow rapid red clover growth. To avoid smothering the red clover, straw should be removed from the field within a day or two of grain harvest, or shredded and evenly distributed across the field if it’s not needed as another cash crop or for bedding livestock on the farm.

The ISU/Tilth Lab research has, as noted, successfully demonstrated frost seeding red clover into winter wheat. While red clover tolerates poorly drained soil better than alfalfa, soils saturated for extended periods should be avoided. Fertilizer should be applied to soil low or very low in phosphorus or potassium. If red clover is harvested as forage, fertilizer applicators should account for nutrient removal rates as well. Red clover likes soil pH above 6.0.

Avoid buying seed labeled “variety not stated,” “common” or “medium” red clover. Instead, check the UW’s extensive red clover variety testing results. Seed should be inoculated with Rhizobium bacteria to facilitate N fixation.

Red clover should be frost seeded at 15 to 20 pounds per acre. While higher rates increase forage yields some, they aren’t economically justified, according to this ISU team.

Frost seed when the ground is still frozen by simply broadcasting seed on the soil surface; this will minimize the impact of wheel traffic on the winter wheat. Freezing and thawing action, in addition to spring precipitation, creates good seed-to-soil contact for germination and stand establishment. Most seed and fertilizer spreaders work for frost seeding, which can be done simultaneously with dry fertilizer application, too. Combining frost seeding and nitrogen in one operation cuts field traffic and cost. The red clover won’t need any additional management until after the wheat is harvested.

Red clover as green manure make ‘cents’

Research shows N supplied by red clover is equal or more profitable than systems using N fertilizer. It’ll provide at least 80 pounds per acre for a subsequent crop of corn. However, yield response to N supplied by red clover is more variable than fertilizer. But late-spring soil nitrate tests in corn following red clover can be used to determine if additional N fertilizer should be sidedressed. This approach is most promising for fall-killed red clover, as these tests underestimate the N contribution from spring-killed clover.

There are many ways to manage red clover as green manure, including tillage and spraying in both fall and spring. Plowing red clover provides two times more N to a subsequent crop of corn as chemical control. Zone tillage of clay loam soil following red clover produced corn yields similar to conventional tillage.

The high N content of red clover residue accelerates decomposition of the wheat residue.

There are several advantages to autumn chemical kill of red clover before planting no-till corn, including earlier planting date, warmer soil condition, reduced risk of dry seedbed conditions and les clover competition with early corn growth.

Red clover residues decompose fast after spring kill with half the N released within four weeks after burial and very little N released after 10 weeks. Gibson notes that when red clover is killed prior to planting, N is released from residue in synch with the corn’s N uptake. Delaying red clover kill from fall to spring doesn’t increase n availability though. Killing the forage legume in the fall or early spring can b effective for limiting soil water loss without sacrificing benefits to a subsequent crop, he adds.

Red clover can be used as forage for one to four years. In a one-year system, you can get two harvests, with first cutting when 10 percent of the plants are in bloom and second cutting before a killing frost in early October. A harvest in early Mary before corn planting can also be taken the following spring. Work in Iowa shows an average combined yield of two cuttings in the establishment year of red clover frost seeded into wheat at 15 pounds to the acre of 2.3 tons, with another 1.5 tons taken off the following spring.

When the red clover will be grown for two or more years, first-cutting in the seeding year should be taken when 10 percent of the plants are in bloom, but the last summer cutting made by early September. Cuttings in the second and third years should also be timed when 10 percent of the plants are in bloom. The first spring cutting will occur in early June (in Iowa and southern Wisconsin). Cutting at 10 percent bloom will provide three cuttings a year. If summer rainfall is good, clover can be cut every 35 to 42 days.

If the stand will be maintained the following year, it’s important to give plants about 45 days between the last cutting and freeze-down. An additional harvest (or grazing) can be made after a hard freeze, but red clover, as farmers well know, is notoriously tough to dry for dry hay.

What’s more, if summer weather turns hot and dry, clover growth may almost stop and sometimes very short plants will start to bloom, and haying them will be impractical.

Red clover quality doesn’t decline as fast with maturity as alfalfa does. It’ll hold high quality until about 40 to 50 percent of the stems have blooms. This means a longer period over which high-quality forage can be harvested. Even so, this ISU team points out that red clover often isn’t harvested soon enough, resulting in poor regrowth and lower yields. When harvested as late as full bloom, new growth from the crown will have started to elongate. Those young shoots are removed during a delayed harvest, resulting in a sharp reduction in the next growth.

Gibson maintains that winter wheat and red clover intercrop can be used to lengthen crop rotations. The system has the potential to increase revenue relative to spring cereal grains while providing N for subsequent crops and high value forage. But as with any cropping system, he warns that “success” depends on “careful management of system components.”

Comments »

Comment on this story

Comments will be approved within 48 hours

Name:

Email: (optional)

Comments:

Image Verification: (Case sensitive)