GRAPHITE-NITROGEN SUSPENSIONS WITH SELECTED HERBICIDES APPLIED TO SNOW COVER IN MANAGEMENT OF WINTER WHEAT

Abstract

Applying darkening agents, such as fly ash or graphite, to decrease the melting time of snow over winter wheat is becoming a common practice in the intermountain west. Snow removal can decrease the susceptibility of wheat or other small grains to snow mold (Typhula incarnata or Fusarium nivale), two genera of fungi that thrive at very low soil temperatures. Temperatures favoring development of those fungi are ideal at the snow-soil interface, particularly when the soil surface is not frozen. Fertility-management practices for winter wheat in this region have included applying 60–70% of the total nitrogen (N) needs of the small grain on a preplant basis in the fall, generally as anhydrous ammonia. The remainder of the fertilizer is top-dressed as UAN in the spring. An experiment initiated in the winter of 1986 determined the effectiveness of applying all the N needed by small grains in the winter with a graphite-UAN suspension fertilizer. This method combines management practices and enabled us to relate snowpack (available moisture) to total N needs. We also compared the effectiveness of different graphite materials to fly ash, the standard material used to increase snowmelt. At one location, herbicides normally applied postemergence to wheat in the spring were instead combined with graphite-UAN and applied over the snow. Three field experiments were established in February 1986. All experimental locations utilized a randomized complete block design with four replications. The first and second locations were dryland wheat areas on the Utah-Idaho border. The third location was a range site 32 km east of Logan, Utah, at an elevation of approximately 2440 m. Data collected at the sites indicate that applying 10 kg ha-1 of graphite can be just as effective in melting snow as applying either 225 kg ha-1 fly ash or 20 kg ha-1 graphite. There were significant differences among treatments in soil nitrate levels, plant tissue nitrate levels, and size and plant populations at Location 1, which indicates that application of N in a graphite solution can be useful in the management of fall-planted wheat. Wheat yields also varied significantly (0.01% level) among the various N treatments applied to the snow surface with graphite. Herbicide-graphite treatments were also effective in controlling broadleaf weed populations in wheat-producing areas.