Remember your first encounter with classic Chinese mustard? Your seared sinuses? Your cheeks washed with involuntary tears?
What you tasted was the indelicate reaction of the mustard plant’s chemical compounds, probably enhanced by the wetness of your mouth.
That same volatile reaction is being applied by Columbia Basin farmers to control pests and weeds, improve the productivity of their soils, reduce the use of chemicals, and improve air quality for downwind communities.
Mustard is becoming the crop of choice as a green manure grown in the rotations of many potato producers. Research is showing that in addition to improving the physical and chemical characteristics of the soil by adding organic matter, mustard and other plants can actually provide the same kinds of protection against disease and pests as applied chemicals do.
From his Grant County office in Ephrata, Andy McGuire coordinates much of the study and evaluation of green manure applications. McGuire is the Lauzier Agriculture Systems Educator, the single endowed extension agent position within Washington State University’s Cooperative Extension system.
While McGuire points out that the complexity of the soil environment makes it difficult to measure the specific biological processes involved, he says the effects of green manure on soil-borne pests are the result of several interacting mechanisms.
Biofumigation is one of those mechanisms attracting considerable attention, because it works in quite the same way as commercial fumigants applied before potato planting. Mustard contains glucosinolates, biologically active chemicals that give it its biting taste. When turned under, the glucosinolates break down into isothiocyanates (ITCs), which are known to kill or suppress soil-borne diseases, nematodes, and weed seeds. In many circumstances mustard ITCs can replace the methyl ITC that is the active chemical produced when commercial metam-sodium is applied.
Scientists are also examining other important biological mechanisms, identified as competitive exclusion and induced resistance. They believe that the disease verticillium wilt may be suppressed when the organic material of mustard helps beneficial organisms out-compete the verticillium organism which infect the roots of potato plants. Similar in concept, they believe, is disease suppression that occurs when beneficial organisms secrete chemicals that induce the resistance of plants to insect-borne diseases.
When McGuire left Nebraska to join the staff of WSU’s Center for Sustaining Agriculture and Natural Resources in 1999, Columbia Basin farmers were growing about 1,800 acres of mustard as a green manure. One of the earliest and most enthusiastic advocates for the practice was Dale Gies, a WSU alum who operates the family farm near Moses Lake.
With McGuire providing farmers with a wealth of information about the benefits of mustard, and Gies the mustard seeds, the acreage numbers have grown to over 20,000. “These approaches have been accepted more rapidly than we expected, but there’s still plenty of opportunity for growth,” McGuire says. Potatoes currently are grown on more than 170,000 acres.
McGuire and farmers also are exploring the benefits of other green manure crops and farming methods with plant scientists from Italy, Australia, and Germany, where the government pays farmers for incorporating green manure into their cropping systems.
The broader benefits of green manures are returned to the public at large, says McGuire. The organic material significantly reduces soil’s susceptibility to water and wind erosion. Air pollution studies of areas east of the Columbia Basin, including Spokane, have linked small, wind-blown particles to respiratory illnesses.
In April, WSU researchers from Pullman used a portable wind machine to measure erosion in a field treated with green manures. “They ran the velocity up to 100 miles an hour and couldn’t get the dirt to blow,” says McGuire.