Botanical composition of native hay meadows throughout the True Prairie bas shifted from predominantly native, warm-season grasses to introduced, cool-season species following mismanagement. To determine if a shift in CO!Jlposition back to warm-season grasses and subsequent increased seasonal production could be achieved, atrazine (2-Chloro-4-{ethylamino)-6-{isopropylamino)-s-triazine) herbicide in combination with N and P fertilizer was evaluated on an eastern Nebraska subirrigated meadow. The soil is classified as a Lawet Vlll"i\lllt fine sandy loam (fine-loamy, mixed (calcareous), mesic Fluvaquentic Haplaquoll). Five rates of N (0, 45, 90, 135, and 180 kg ha -•), two rates of P (0 and 34 kg ha -•), apd two rates of atrazine (0 and 2.2 kg ha-•) in factorial combination were arranged in a randomized complete block design. Atrazine and P were applied in late April to late May, and N was applied in early June in 1982 through 1984. A combination of 180 kg N ha-• and 34 kg P ha-• produced dry matter yields 95, 101, and 77% greater than untreated plots in 1982, 1983, and 1984, respectively. Atrazine altered botanical composition from predominantly cool-season grasses to predominantly warm-season grasses. Changes ·in species composition by weight indicated a twofold increase in warm-season yield. This shift in seasonal distribution of yield was accomplished without a reduction in total dry matter yield compared with plots recieving 180 kg N ha -• in combination with 34 kg P ha-1 • · Additional index