Tallgrass prairie vegetation response to spring burning dates, fertilizer, and atrazine.

Abstract

Tallgrass prairies provide an important source of hay and summer forage in eastern Nebraska. A study was conducted in 1989 and 1990 on 2 late seral tallgrass prairies near Lincoln and Virginia, Nebraska to determine if production of selected components of tallgrass prairie communities could be altered by burning (not burned, or burned in either early, mid-, or late spring)and applying fertilizer (0 and 67-23 kg N-P ha-1) and atrazine [6-chloro-N-ethyl-N'-(1-methylethyl)-1,3,5-triazine-2,4-diamine] (0 and 2.2 kg a.i. ha-1). Vegetation was harvested the year treatments were applied at about 30-day intervals starting in June and ending in August. Maximum big bluestem (Andropogon gerardii var. gerardii Vitman) accumulated standing crop (ASC) on unburned areas and areas burned in mid-spring occurred later in 1990 than in 1989. Burning in late spring 1989 maintained big bluestem ASC above 1,100 kg ha-1 through July, whereas big bluestem ASC declined below 840 kg ha-1 in July on areas where other burn treatments were applied. In 1990, big bluestem ASC exceeded 1,570 kg ha-1 in June on areas burned in early and midspring and exceeded 1,500 kg ha-1 in July on areas that were not burned or burned in mid- or late spring. From July to August 1990 big bluestem ASC declined below 730 kg ha-1 for all treatments except the late spring burn treatment where ASC was 1,340 kg ha-1. Burning in late spring reduced prairie dropseed [Sporobolus heterolepis (A. Gray) A. Gray] and tall dropseed [S. asper (Michx.) Kunth.] ASC by at least 67% in June 1990 compared to areas burned in early and mid-spring. Cool-season grass ASC at Virginia declined 86% in June when burned in late spring compared to areas that were not burned. Fertilization increased big bluestem ASC by about 23 and 29% in June and July. Vegetation response to atrazine was variable. Atrazine had a negligible effect on big bluestem ASC. Burning late seral tallgrass prairie in late spring increased big bluestem ASC later in the growing season and decreased cool-season grasses more effectively than burning earlier in the spring.