Effect of Fertilizer Applications and Grazing Exclusion on Species Composition and Biomass in Wet Meadow Restoration in Eastern Washington

Effect of fertilizer applications and grazing exclusion on species composition and biomass in wet meadow restoration in eastern Washington. Fertilizer applications and grazing exclusion were used as restoration strategies in degraded wet meadows in eastern Washington to grow biomass in the root systems where it could not be grazed. We used a split-block design to test vegetation responses to six fertilizer rates, eight fertilizer types, and three grazing treatments after three growing seasons. Little change in plant composition was detected, but weed biomass was reduced by 50 percent in cattle plus elk grazing. Although forb shoot biomass did not increase, grass shoot biomass doubled but was influenced by grazing treatments. Root biomass doubled under fertilizer applications. A 10-percent decline in soil bulk density suggested a reduction in soil compaction. These responses were attributed to the increased root biomass. Optimum fertilization rates of 100 kg/ha were recommended along with carefully administered grazing schedules for meadow community restoration. Abstract Many meadows on the east slopes of the Cascade Range in Washington are being overused. This is thought to be causing shifts in plant communities to early-succession stages or infestations of introduced species (weeds). We used treatment combinations of grazing exclusion and fertilizer applications of varying rates and mixtures to document changes in plant communities, to evaluate shoot and root biomass, and to examine effects on soil properties in four east-slope meadow areas near Yakima, Washington. There were no clear changes in plant community composition associated with any treatment combinations for the period of the study. Grazing treatments appeared to affect as much as a 55-percent decline in nonnative plant species. Grass shoot biomass increased by 400 kg/ha in no-grazing treatment. For forb biomass, there were no clear patterns of fertilizer or grazing effects. Root biomass doubled to an average of 90 µg/cm 2 with fertilizer treatments after three seasons. Soil compaction increased by 19 percent in cattle grazing treatments but decreased by 8 percent where only elk grazed. Water well depths increased, but this could not clearly be attributed to effects of the treatment. For the meadows in this study, we conclude that no particular mix or rate of fertilizer contributed to plant community changes or to shoot biomass accumulations. Root bio-mass, however, clearly improved overall treatment types and levels. We saw some evidence that nonnative (weed) to native plant ratios can be reduced by limited grazing activity. When livestock grazing was …