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Using Rye As A Living Mulch In Soybeans

With increasing concerns about herbicides and environmental problems, more innovative ways of controlling weeds need to be studied. Living mulch may be an option for producers using an integrated weed management system, according to Jerry Doll, extension weed scientist in the College of Agricultural and Life Sciences at the University of Wisconsin-Madison.

Trials at the Arlington Agricultural Research Station showed that spring-planted rye as a living mulch can control weeds without reducing soybean yields. However, conditions have to be right. For best results, weed pressure should be low and soil moisture adequate for the soybeans and the rye. Also, the rye should provide enough ground cover to out-compete weeds.

Rye has several benefits as a living mulch. It contributes organic matter, reduces soil erosion, inhibits weeds and may also have an allelopathic effect. However, managing rye as a living mulch can be challenging, Doll says.

Doll and graduate student Comfort Ateh conducted trials from 1992 to 1994 on silt loam soils that had previously been planted in corn. The corn was harvested as grain; fields were chisel plowed in the fall and tilled with a field cultivator and cultimulched the next spring. Rye was then planted along with soybeans in narrow rows. The rye went in either before or along with the soybeans.

Rye was planted at three seeding rates and weed management in each seeding rate were: rye and no additional weeding, rye with rotary hoeing, rye with selective herbicides, and rye killed with herbicide. The control plots were soybeans without rye and either no weed control or chemical weed control.

Results showed that rye suppressed weeds by 90, 82 and 60 percent in 1992, 1993, and 1994, respectively, compared with the no-rye weedy control plot. There were higher weed densities in the rotary hoed plots than in the living mulch plots, showing that the rotary hoe did more damage to the rye than it did in controlling weeds.

Moisture was the biggest limiting factor in the system, especially in plots that had rye and weeds. However, rye seeding rates had little to no effect on soybean vigor when moisture was adequate. The time of rye planting also had no effect on soybean vigor. “This means that producers could rig up a system to put rye on the field and plant soybeans in one trip,” said Doll.

The picture gets more complicated when comparing marginal returns. 1992 was a dry year and soybean yields were low. Due to decreased seed and herbicide costs the plot with the lowest rye seeding rate had the highest returns, although, better weed control was achieved by a medium seeding rate that year.

In 1993, when moisture was adequate and conditions were good for soybean growth, marginal returns were not affected by the rye seeding rate. There also were no differences in yield between rye and weed-management systems in 1993. Producers need to take into account cost, not just yield, when considering living mulch as a weed-control system, Doll says.

A combination of herbicides, mowing, and natural infections can help suppress a living mulch, but some situations may not be suitable for this system. “If you are relying on post-emergent grass herbicides to kill the rye, it not only is expensive but you are also giving broadleaf weeds the opportunity to thrive,” said Doll. Using Roundup-Ready soybeans with a living mulch may give you an additional management option if you have to kill the mulch because of moisture concerns, he says.

“For producers who might like to try rye in a soybean system and learn the ropes,” Doll says, “a safer strategy to start with would be a fall-planted rye. Rye can be planted after wheat, corn silage or a vegetable crop. Then you would kill the rye in the spring at the time of soybean planting. Killing the rye in the boot stage would ensure reasonable allelophathic effects, and these will be maintained if soybeans are no-till planted. Previous research showed that this system had little risk of reducing soybean yields. From my 20 years of experience in Wisconsin, most of the time you aren”t jeopardizing moisture and would benefit from the cover crop.”