RESPONSE OF BROMEGRASS TO NITROGEN FERTILIZATION. II. GRASSLANDS GALA,**

Abstract

ABSTRACT Grasslands “Gala” (Bromus stamineus Desv.) bromegrass is generally regarded as high quality forage particularly adapted to grazing, but little is known about its growth response to N fertilization or potential to accumulate nitrate (NO3 −). Effects of N fertilization were investigated in two greenhouse experiments. Gala was grown in pots in a complete randomized design with four replications of the following N treatments: 0, 25, 50, 100, and 200 kg N ha−1 applied twice in Experiment 1, and 50, 100, 200, 300, and 400 kg N ha−1 applied five times in Experiment 2. Plants were harvested twice in Experiment 1, and five times in Experiment 2. Twenty-five kg N ha−1 per application did not sustain growth of Gala but little increase in growth occurred beyond 50 kg N ha−1 over five applications. About 90% of the 250 kg N ha−1 that was applied in 50 kg-increments was measured in the aerial plant biomass. Yield efficiency was also greatest at 50 kg N ha−1 per application and decreased with increasing N levels. Five applications of N at any rate tested decreased soil pH and increased accumulation of NO3 − in the soil. Nitrate accumulated in the plant at N application rates above 50 kg ha−1. Frequent low rates of N appear necessary to avoid N accumulation in soils, to promote high N use efficiency by Gala, and to avoid a potential for NO3 − toxicity to grazing ruminants.