Data on the effects of livestock grazing on soil nutrient availability are virtually nonexistent for meadow systems. We measured the effect of livestock grazing on soil, emphasizing soil-solution chemistry, in a Sierra Nevada riparian meadow. Treatments were livestock exclusion (begun in 1989) and grazing to leave 1 000 kg ha À1 of vegetation. Ceramic tension lysimeters were placed in the treatments (2 replicates) by landscape position (stream edge, midfloodplain, and forest edge), and by depth (approximately 0.1, 0.6, and 1.2 m below the soil surface). Lysimeter water was extracted twice monthly in April, May, and June of 1990 through 1993, and cations and anions were quantified. In addition, KCl-extractable NO 3 À and NH 4 þ ; bicarbonate-extractable ortho-P; available Mn, Cu, Fe, and Zn; and root-length density (RLD) were quantified in soils by treatment, landscape position, and soil depth in July 1991 and September 1993. RLD was not affected by grazing. Significant (P 0.05) treatment effects were largely limited to the forest edge. The grazed treatment had greater lysimeter-extractable Na þ , Ca þ2 , Mg þ2 , and NO 3 À ; higher pH; and less K þ and NH 4 þ than the excluded treatment. Compared with corresponding excluded treatments, bicarbonate-extractable P was significantly greater on the grazed forest edge, and available Mn was significantly greater at the grazed stream-edge position in 1991. Extractable NO 3 À was significantly higher in the 0-25 cm depth increment of the grazed treatment, and available Zn was significantly greater on the grazed midfloodplain position in 1993. Grazing did not result in more anoxic soil conditions than the excluded treatment. Grazing effects were most pronounced at the forest edge, possibly as a result of spatial transfer of nutrients via cow urine and feces. Management goals to sustain highelevation meadows should emphasize maintenance of high RLD to sequester soil nutrients.
ResumenVirtualmente no existen datos del efecto del pastoreo animal en la disponibilidad de nutrientes del suelo en sistemas de praderas. Medimos el efecto del apacentamiento del ganadosobre el suelo, enfatizando en la química de la solució n del suelo en una pradera ribereñ a de la Sierra Nevada. Los tratamientos fueron, exclusió n al ganado (desde 1989) y apacentamiento hasta dejar 1 000 kg ha À1 de vegetació n. En los tratamientos se colocaron lísimetros cerámicos de tensió n (dos repeticiones) en cada posició n del paisaje (orilla de cauce, cauce medio y límite del bosque) y por profundidad (aproximadamente 0.1, 0.6, y 1.2 m bajo la superficie). El agua del lísimetro se extrajo dos veces por mes, en abril, mayo, y junio de 1990 a 1993 y se cuantificaron los aniones y cationes. Ademá s, se cuantifico el KCl-extractable; NO 3 À y NH 4 þ ; ortho-P extractable con bicarbonato; Mn, Cu, Fe, y Zn disponibles; y la densidad de la longitud raíz (RLD), estas determinaciones se realizaron por tratamiento, posició n del paisaje y profundidad de suelo en julio 1991 y septiembre 1993. RLD no fue afecta...