Soil Attributes in a Sierra Nevada Riparian Meadow as Influenced by Grazing

Abstract

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-1 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 NO3 and NH4+– 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+, Ca+2, Mg+2, and NO3; higher pH; and less K+ and NH4+ 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 NO3 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 high-elevation meadows should emphasize maintenance of high RLD to sequester soil nutrients.