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Available water influences field germination and recruitment of seeded grassesPeriodic summer rainstorms in some semi-arid regions result in variable soil moisture and differential establishment of seeded species. A 2-year study investigated soil water effects on germination and survival of 6 native and 2 non-native southwestern U.S. grass species. Bags of seeds were buried and retrieved before and during the summer rainy season. High field germination in seed bags (20-100%) and limited germination in the laboratory of seeds that were ungerminated in seedbags (0-45%) were exhibited by 6 native grasses following initial rainfall events in which the surface soil was saturated for 2 days or water potential (1-3 cm depth) was above -1.5 MPa for more than 9 days. Fewer Lehmann lovegrass (Eragrostis lehmanniana Nees) seeds germinated in response to initial and subsequent rainfall events (0-49%), but this species retained more residual germinable seeds (49-99%) than all other species studied. For 2 sowing dates, the soil drying front exceeded estimated seminal root depth 13 days after germination. Lack of recruitment for some species sown on these dates was probably due to seedling desiccation before adventitious roots had sufficient time to develop. The ability of Lehmann lovegrass to retain a viable seedbank when rainstorms are separated by long dry periods allows it to establish better than some native grasses that germinate quickly and are then subject to seedling desiccation. During a summer with more consistent rainfall, native species recruitment was greatest when seeds were planted during, rather than before the summer rainy season.
Establishment and Yield Responses of Warm-Season Grass Strains to FertilizationEffects of nitrogen and phosphorus fertilization on stand establishment and yield of 5 warm-season prairie grasses were observed on 12 problem sites in Nebraska. Annual nitrogen fertilization after the establishment year maintained superior stands and increased forage yields of the experimental varieties. Proper timing and rate of nitrogen fertilization produced vigorous growth of the planted grasses which in turn controlled soil erosion and reduced weed invasion; whereas untimely mowing and fertilization increased cool-season weeds. Late-maturing strains of the warm-season grasses produced better stands than early-maturing strains. Where not limited by soil moisture or shortness of season, the late-maturing strains of switchgrass, indiangrass, and big bluestem produced larger yields than early-maturing strains of these grasses.
Soil Moisture Conditions Under Pastures of Cool-Season and Warm-Season GrassesThe season of active growth and water use by warm-season grasses is about five months, May through September, compared with seven to eight months for cool-season grasses. There was less water in the soil in midspring each year under cool-season than under warm-season grasses. Consequently, the cool-season pastures suffered from midsummer drought more often than did warm-season pastures.