Effects of Herbage Allowance on Defoliation Patterns of Tallgrass Prairie

Abstract

Few studies have dealt with measuring individual plant defoliations in the context of intensive grazing management. In May, July, and August of 1987, grazing trials were conducted to quantify the effects of herbage allowance on defoliation patterns of big bluestem [An&opogon gem&i Vitmanl, hrdiangrass [Sorghtrum nutons(L.) Nash], and little bluestem [ScEza&yr~ scqnrrium (Michx.) Nash]. Herbage allowancea of 10, 20,30, and 40 kg AUD" were replicated twice per trial. Tiller height, relative leaf area removed, and lrequency of defoliation were measured every 2 days over loday trials. Indiangrass was the most preferred species in all trials. The rate of leaf area removal increased as herbage allowance decreased. Current guidelines which call for rest periods of 3040 days would result in light to moderate intensity defoliation for indiangrass at all herbage allowances. The maximum percentage of tillers grazed only once per trial ranged from 20 to 9g%1 depending on herbage allowance, species, and trial.Selectivity between species was reduced by decreasing herbage allowance hut this effect was not large until herbage allowance was below 20-25 kg AUD" and selectivity was never completely removed. Grazing all tillers only once in a grazing period, even within a species, is unlikely in a tallgrass prairie community. Leaf area removal was moderate the first time a tiller was defoliated and severe for later defoliations. The goal of grazing any individual tiller at no greater than moderate intensity within a grazing period would he roughly equivalent to grazing any tiller no more than once. However such a goal would require many tillers to go ungrazed.

Tiller Defoliation Patterns under Frontal, Continuous, and Rotation Grazing

“…However, this relationship had a quadratic tit and describes the decline in defoliation frequency as herbage allowance increases. Other researchers (Jensen et al 1990, Curl1 and Wilkins 1982 herbage allowance relationship. Although marked tillers were defoliated at a faster rate under frontal compared to rotation or continuous grazing (Fig.…”

Little Bluestem Tiller Defoliation Patterns under Continuous and Rotational Grazing

“…Clipping little bluestem after apical meristems have been elevated stimulates tillering the first year (Jameson and Huss 1959 (Mullahey et al 1990). This change in the size of plants and plant parts commonly occurs in response to heavy grazing (Hanson et al 1931, Holscher 1945, Weaver and Darland 1947 (Hodgson 1966, Morris 1969, Briske and Stuth 1982, Curll and Wilkins 1982, Hart and Balla 1982, Jensen et al 1990; 2) the relative relationship between defoliation frequency and intensity (Cassady 1953, Owensby et al 1974, Buwai and Trlica 1977, Gammon and Roberts 1978c, Clark et al 1984, Mullahey et al 1990); and 3) the importance of tiller architecture i.e., height, total lamina length and location in the canopy, in determining defoliation probabilities (Greenwood and Arnold 1968, Hodgson and Ollerenshaw 1969, Bartham and Grant 1984, Pierson and Scarnecchia 1987, Heitschmidt et al 1990). …”

Early Summer Grazing Effects on Defoliation and Tiller Demography of Prairie Sandreed

“…El alto grado de correlación entre el porcentaje de hijuelos del "Prairie sandreed" apacentados y el uso del "Prairie sandreed" (R 2 = 0.91 en Junio y 0.90 en Julio) sugiere que el porcentaje de hijuelos apacentados puede ser utilizado para monitorear el uso de esta especie a inicios del verano en el Nebraska Sandhills. Briske 1988, Jensen et al 1990, Hart et al 1993, Allen and Marlow 1994, Derner et al 1994. However, most grazing systems used on semi-arid rangelands are not designed for specific plant species.…”