Response of an Irrigated Cool- and Warm-Season Grass Mixture to Nitrogen and Harvest Scheme

Abstract

Maintaining a mixture of cool-and warm-season grasses under intensive management for season-long production is difficult, due to species shifts, especially to a dominance of cool-season grasses when heavy amounts of nitrogen (N) fertilizer are used. The objective of this study was to determine if high forage yields could be produced season long while maintaining a desirable balance of warm-and cool-season grasses. The study was conducted near Mead, Nebraska on a Sharpsburg silty clay loam (Typic Argiudoll). An irrigated mixture of 3 warm-season grasses and 1 cool-season grass, big bluestem (Andropogon gerardii Vitman), switchgrass (Panicum virgatum L.), and indian-grass [Sorghastrum nutans (L.) Nash] and smooth brome (Bromus inermis Leyss.) was fertilized at low (150 kg/ha), medium (250 kg/ha) and high (350 kg/ha) rates of N in split applications. Three harvest schemes were designed to either produce high quality forage or to maximize yield. Herbage yields showed a quadratic response with N level. A late May/mid July harvest scheme for the first and second cuttings did not produce as much forage as late May/late August or early June/late August harvest schemes. Population of smooth brome and other cool-season grasses declined with the higher N rates. Populations of warm-season grasses were not greatly affected by N level. Density of smooth brome increased under all harvest scheme treatments and the highest increase for other cool-season grasses was with a May 24/July 13 harvest scheme. Warm-season grasses maintained a steady density over the 3 years. Forage was produced from early May until late summer with an irrigated cool- and warm-season mixture. Fall production of smooth brome was minimal, although stand was generally maintained. Nitrate N accumulated in the soil under the medium and high N treatments.