Defoliation Intensity Effects on Season‐Long Dry Matter Distribution and Nutritive Value of Tall Fescue

Abstract

Implementation of intensive grazing management requires knowledge about pasture growth rates and nutritive value throughout the grazing season. Such information is lacking because results from small-plot defoliation experiments generally focus on annual dry matter yields (DMYs) and season mean nutritive value. In this experiment, the influences of defoliation treatments on daily growth rate (DGR) and associated nutritive value of tall fescue (Festuca arundinacea Schreb.) throughout the growing season were evaluated. A 3-yr study was conducted on a Typic Kanhapludult soil near Raleigh, NC. Eight defoliation treatments (31-, 15-, 10- and 8-cm canopy heights cut to a 5-cm stubble; 31-, 15-, and 11-cm canopy heights cut to a 9-cm stubble, and an 8-cm canopy height cut to a 4-cm stubble) were evaluated in a randomized complete block design. Daily growth rates (kg ha -1 ) were significantly (P ≤ 0.01) altered by defoliation treatments and by years within treatments. When rainfall was near normal in both spring and late summer, tall fescue growth rates, depending on defoliation treatment, ranged from 34 to 55 kg ha -1 d -1 in May, from 7 to 18 kg ha -1 d -1 in late July, to 22 to 35 kg ha -1 d -1 in late September. In less favorable years, DGRs seldom exceeded 30 kg ha -1 d -1 in the spring or 15 to 30 kg ha -1 d -1 in the autumn. Depending on defoliation treatments, in vitro dry matter disappearance (IVDMD) ranged between 650 and 733 g kg -1 in the spring, 479 and 687 g kg -1 in midsummer, and 549 and 807 g kg -1 by late summer. Crude protein (CP) and detergent fiber fraction concentrations were also examined. The approach used to estimate DGR and associated nutritive value changes throughout the growing season resulted in useful data that can be applied in developing intensive grazing management practices.