The effect of livestock grazing on organic C and N in rangeland soils
is not well defined. In this study on sandy rangeland in western Oklah
oma, we sampled 8 pastures moderately grazed by cattle and 8 adjacent
exclosures ungrazed by livestock for 50 years. The sagebrush was large
ly controlled by herbicide in the study areas. The C and N concentrati
ons in the surface 5 cm of soil, total herbage production, and total N
uptake by vegetation were similar (P > 0.05) in grazed and nongrazed
areas. Carbon and N concentrations in soils sampled to a constant mass
to a depth of 5 cm or less were not (P > 0.05) different from concent
rations determined on soil sampled to a constant depth of 5 cm. When c
alculated on a content basis, grazing increased (P < 0.001) the bulk d
ensity (1.35 g cm(-3)) compared to nongrazed pastures (1.19 g cm(-3))
and had a significant (P < 0.01) effect on C and N in the surface 5 cm
of soil. Litter and total N in litter were greater (P < 0.01) on nong
razed areas. Little bluestem (Schizachyrium scoparium (Michx.) Nash) a
nd sand bluestem (Andropogon hallii Hack.) produced more herbage and h
ad greater frequency on nongrazed areas, whereas blue grama [Bouteloua
gracilis (H.B.K.) Lag. ex Griffiths], sand dropseed [Sporobolus crypt
andrus (Torr.)Gray], and western ragweed (Ambrosia psilostachya DC.) i
ncreased in frequency on grazed areas. Thus, 50 years of moderate graz
ing by cattle had no measurable effect on C and N concentrations in th
e surface 5 cm of the sandy soil or on total N uptake by plants as com
pared with nongrazed areas; however, significant differences occurred
in species composition which may alter mechanisms of C and N balance.