Effect of a Wetting Agent and Nitrogen Fertilizer on Establishment of Ryegrass and Mustard on a Burned Watershed

A wetting agent was applied by sprinkler irrigation to nitrogen-fertilized plots on a burned watershed in southern California. The wetting agent decreased the total production of mustard (Brassica nigra and B. Campestris) and increased the number of ryegrass seedlings (Lolium rigidum and L. multiflorum). Where a wetting agent was applied, the moisture conditions at the soil surface were more favorable for seedling establishment and the grass was favored over mustard. In a subsequent laboratory experiment, the wetting agent suppressed mustard seedlings but had a lesser suppressive effect on ryegrass. The differential phytotoxicity was presumably responsible for much of the difference between grass and mustard seedling establishment in the field test. Nitrogen fertilizer increased total plant production and in combination with the wetting agent further enhanced the establishment of ryegrass, but not mustard.