NITROGEN INTERACTIONS WITH MEDUSAHEAD (TAENIATHERUM-CAPUT-MEDUSAE SSP. ASPERUM) SEEDBANKS

Medusahead is an invasive annual grass that, once established, severel y affects rangeland productivity and stability. Medusahead builds larg e seedbanks in the litter and on the soil surface. Effective weed cont rol of medusahead involves either inhibiting germination from the seed bank, eliminating the seedbank, or enhancing germination so that plant s are available for control. The purpose of this study was to determin e the influence of nitrogen enrichment, immobilization, and nitrificat ion inhibition treatments in the field on the size and germination sta tus of medusahead seedbanks. The germination status of medusahead seed s in seedbanks was determined by periodically collecting field samples of surface soil and litter and bioassaying them in greenhouse emergen ce tests. Control seedbanks had increased seedling emergence with KNO3 or GA(3) enrichment of the bioassay substrate. The combination of the se two materials increased emergence. Nitrogen enrichment increased se edling establishment in the field. Carbon enrichment in the field decr eased seedling establishment and increased medusahead seeds in seedban ks. Nitrapyrin treatment decreased medusahead in the field similar to carbon enrichment. In comparison to the control or other treatments, G A(3) enrichment was not as effective in increasing emergence from nitr apyrin-treated bioassay samples. The combination of carbon and nitrapy rin treatments was very effective in eliminating medusahead emergence in the field, but in wetter years, it never completely eliminated medu sahead seedling recruitment and subsequent reproduction. These treatme nts have promise for influencing succession in medusahead infestations if an adapted perennial species, capable of competing under low nitro gen levels, becomes available.