Submitted to: Rangeland Wire
Publication Type: Other
Publication Acceptance Date: 5/15/2001
Publication Date: 12/13/2001
Citation: MACKOWN, C.T., JONES, B., JONES, T.A. 2001. COOL-SEASON GRASS ESTABLISHMENT: EFFECTS OF N ON GERMINATION AND GROWTH TRAITS OF DESIRABLE PERENNIAL VS WEEDY ANNUAL SEEDLINGS. RANGELAND WIRE, OKLAHOMA SECTION, SOCIETY FOR RANGE MANAGMENT. Volume(10)p. 2-3. Interpretive Summary: In the Intermountain West and elsewhere, grazinglands and disturbed rangelands are plagued by infestations of two undesirable cool season annual grasses, cheatgrass and medusahead. These non-native grasses have decreased the productivity of millions of acres of grazinglands, decreased the biological diversity of grazinglands, and increased the incidence and severity of wildfires. Recent field research revealed that on disturbed rangeland soils, decreased availability of mineral nitrogen (N) favors establishment of desirable perennial cool-season grasses in the presence of annual invasive cool-season grasses. To better formulate management strategies to overcome infestations, we conducted controlled N nutrition experiments to determine if the biological basis for the field observations was the consequence of seedling germination and growth response to availability and forms of mineral N. Our experiments demonstrated that germination of the undesirable annuals and desirable native cool season perennial grasses was unaffected by the availability or the form of mineral N. Also, the competitive advantages leading to establishment of invasive annuals instead of desirable native perennial grasses appear to be determined more by vigorous seedling growth of the annuals than differences in the response of the grasses to N supply or form of mineral N. These results will be useful to managers seeking to decrease infestation of our grazinglands by undesirable cool season annual grasses.
Technical Abstract: Annual weed infestation is often a problem during establishment of cool- season perennial grasses on grazinglands and particularly on disturbed rangeland. In the intermountain west and elsewhere, two invasive annual cool-season grasses, cheatgrass and medusahead have decreased the productivity of millions of acres of livestock and wildlife grazinglands, decreased the biological diversity of grazinglands, and increased the incidence and severity of wildfires. Recent field research reveals that on disturbed rangeland soils, decreased availability of mineral nitrogen (N) supplied to plants favors establishment of desirable perennial cool-season grasses in the presence of annual invasive cool-season grasses. In addition, the desirable perennials seem to compete better on disturbed rangeland soils when mineral N is primarily in the form of ammonium rather than nitrate, the final form of mineral N produced in the biological conversion of soil organic N to mineral forms of N used by plants. To account for the these observations and identify appropriate management strategies to enhance the establishment of desirable perennial cool-season grasses in the presence of invasive annual grasses, fundamental knowledge of the effects of N nutrition is required. We conducted controlled N nutrition experiments to determine seedling germination and growth responses to availability and forms of mineral N.