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Managing Alfalfa For Reduced Soil Erosion Companion Crops No Longer Sacred, Research Shows

Managing crop residues and ground cover for erosion control is important when establishing, maintaining and rotating out of perennial forages, say researchers at the College of Agricultural and Life Sciences. The researchers studied establishing alfalfa with an oat cover crop, growing alfalfa with smooth bromegrass, and killing alfalfa in spring or fall.

The studies focused on erosion and non-point source pollution in the Mississippi Driftless Region, which covers 10.4 million acres in the Upper Mississippi Valley. According to the Natural Resources Conservation Service, current erosion levels are 6 to 15 tons of soil loss per acre per year on farmed land. The eroded soil carries phosphorus and other contaminants into rivers, lakes and streams.

“The goal of our research was to document the environmental and economical advantages of what we believed to be best management practices,” said agronomist Nyle C. Wollenhaupt, formerly with the University of Wisconsin-Madison, currently an agronomist with the Soil Teq, Division of Ag Chem Equipment Company.

The first of the three research projects examined oats as a companion crop in establishing alfalfa. “It has been held as sacred that a cover crop provides erosion control when establishing alfalfa,” said Wollenhaupt. “We found that in the early spring period, after tillage and before the cover crop is big enough to protect the soil, substantial erosion may occur. Thirty percent or more crop residue on the surface is needed to prevent excessive erosion.” The research shows that establishing alfalfa in previous crop residues with no-till or conservation tillage is more important than using a companion crop for erosion control.

The second project looked at alfalfa and smooth bromegrass erosion control. Researchers established 20 percent bromegrass in the alfalfa stand, assuming utilization by dairy farmers. “This research concludes that adding bromegrass to alfalfa at 20 percent did not reduce erosion rates from those seen in pure stands of alfalfa,” said agronomy graduate student Robert Zemenchik. “But all of the trials (alfalfa, alfalfa-bromegrass, and bromegrass) had far less erosion than row crops.” The research showed in well-managed alfalfa only 0.3 tons per acre per year of soil is lost, and in most years less.

Farmers who can utilize pure bromegrass should use it on steep slopes for better erosion control than alfalfa. For farmers not able to utilize bromegrass, maintaining ground cover with alfalfa is important. “The longer the life of a stand is extended through improved management, the more soil erosion can be reduced by not having to plant as often,” said agronomist Ken Albrecht.

The last project evaluated spray-killing alfalfa as a best management practice, instead of plowing under an old alfalfa stand. Researchers measured erosion in fall-spraying versus spring-spraying when killing alfalfa before rotating into no-till corn. “Erosion occurs in the early spring. Fall-killed alfalfa did not generally provide enough ground cover (less than 30 percent),” Wollenhaupt said. One exception was a fall-killed stand that contained 40 percent grass. Ground cover of this stand was 30 to 40 percent in the spring, bringing erosion to within the allowable limit without affecting corn yields.

On the other hand, spring-killed alfalfa minimized erosion but reduced corn yields. “The yield loss may have been the result of the alfalfa using soil water before the crop was killed, and/or cooler soil temperatures at corn planting,” Wollenhaupt said. Studies now underway look at zone tillage in spring-killed alfalfa and profitable yields in corn.

Using conservation tillage to establish alfalfa, improving the quality and life of alfalfa stands, and fall spray-killing a grassy alfalfa stand can reduce soil erosion in an alfalfa-corn rotation. The researchers found that these best management practices can reduce soil erosion by 2 to 10 times the amount seen in traditional practices. “The main finding in the three research projects is that protective cover over the soil at all times in the alfalfa-corn rotation is needed to prevent soil erosion,” said Zemenchik. “When we reduce soil erosion we preserve soil resources and reduce the movement of phosphorus and other contaminants into streams, lakes, and rivers.”

This research was conducted at the Lancaster Agricultural Experiment Station from 1992 to 1994, and was part of state funded water quality research.