Atrazine and fertilizer effects on Sandhills subirrigated meadow.

Abstract

Many Nebraska Sandhills subirrigated meadows have shifted to predominantly cool-season grasses. Meadows are often cut in July when forage quality of cool-season is lower than that of warm-season species. The objective of this research was to evaluate a one-time application of atrazine [6-chloro-N-ethyl-N'-(1-methylethyl)-1,3,5-triazine-2,4-diamine] in restoring dominance of warm-season grasses and to determine if nitrogen (N) with and without phosphorus (P) would enhance or prolong the atrazine effect on species composition, yield, crude protein, and in vitro dry matter digestibility (IVDMD). Atrazine was applied once at 0, 2.2, and 3.3 kg/ha in spring or fall 1983 and 1984 to a Gannett fine sandy loam (coarse loamy mixed mesic Typic Haplaquoll). The year after atrazine application one-half of each spring-treated plot was fertilized with N (50 kg/ha). One-half of the fertilized area received P (18 kg/ha). Both spring and fall applied atrazine decreased cool-season grass species composition and yield. Spring-applied atrazine reduced first-year yields, but yields recovered by the end of the second year. Conversion of plots to warm-season grasses increased crude protein in mid-July for 2 growing seasons. Percentage IVDMD was increased the year of atrazine application on both sets of plots and also the year following application on the 1983-treated plots. A single fertilizer application did not enhance or prolong the effect of atrazine on forage quality. Cool-season grasses regenerated in atrazine-treated plots after 2 years so changes in yield and quality were only temporary, making atrazine use in subirrigated meadows uneconomical.