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Title: DEFOLIATION INTENSITY EFFECTS ON SEASON-LONG DRY MATTER DISTRIBUTION AND NUTRITIVE VALUE.

Author
item Burns, Joseph
item CHAMBLEE, DOUGLAS - NORTH CAROLINA STATE UNIV
item GIESBRECHT, FRANCIS - NORTH CAROLINA STATE UNIV

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/12/2002
Publication Date: 8/20/2002
Citation: Burns, J.C., Chamblee, D.S., Giesbrecht, F.G. 2002. Defoliation intensity effects on season-long dry matter distribution and nutritive value.. Crop Science.

Interpretive Summary: Tall fescue is a major forage species grown throughout the North-South Transition zone. In this region tall fescue provides the major source of pasture from late March into late June with a secondary period of growth from September through November. In developing extensive grazing systems there is a need to know the daily growth rate of tall fescue throughout the grazing season. This provides information about the amount of forage available per unit land area at any interval and the daily stocking density that can be applied to effectively utilize the forage produced. Also, there is a need to know the nutritive value of the forage being produced so a producer will be able to estimate the daily performance that he can expect from his animals. This information will assist in determining appropriate allocation of forage including the number of paddock needed and the land area that should be allocated daily. In essentially all defoliation-type studies only annual mean dry matter yields are presented along with the annual weighted means for nutritive value estimates. This paper provides an approach and is one of the first efforts in this region to present forage growth curves of tall fescue from a number of defoliation intensities and provides an estimate of the nutritive value of the forage throughout the grazing season. The findings in this paper will assist in developing on-farm intensive grazing systems which employ a short period of herbage allowance (1 to 5 days) in a rotational grazing system.

Technical 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 and season mean nutritive value. In this experiment the influences of defoliation treatments on daily growth rate 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 Hapludult 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, daily growth rate 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 ranged between 650 and 733 g kg-1 in the spring, 479 and 687 g kg-1 in mid-summer and 549 and 807 by late summer. Crude protein concentration of selected treatments ranged between 145 and 210 g kg-1 in spring, 112 and 165 g kg-1 in mid-summer and 140 and 215 g kg-1 in late summer. Neutral detergent fiber concentrations increased as the season progressed and ranged between 483 and 515 g kg-1 in mid-spring, 509 and 598 g kg-1 in mid-summer and decreased to between 417 and 499 g kg-1 by early autumn. The approach used to estimate daily growth rate and associated nutritive value changes throughout the growing season resulted in useful data that can be applied in developing intensive grazing management practices.