Influence of Livestock Grazing, Floodplain Position, and Time on Soil Nutrient Pools in a Sierra-Nevada Montane Meadow

Abstract

Limited data exist on quantification of soil nutrient pools in montane meadow ecosystems. Along Big Grizzly Creek in the Plumas National Forest, CA (June 1999-September 2005), soil nutrient pools were quantified by livestock grazing treatment (grazed, ungrazed), floodplain location (stream edge, midfloodplain, forest edge), and season using resin capsules (15-cm depth) and bulk soil samples (0- to 25-cm depths). Resin capsules integrated nutrient availability for three periods: overwinter, plant growth, and senescence. Bulk soil samples were collected immediately after snowmelt (pregrowth), during plant growth, and during plant senescence. During the study period, pulses of N or P did not occur, suggesting strong coupling of mineralization with root/microbial uptake. Soil availability of most nutrients was affected by sampling time and floodplain location; however, differences were small. Soil samples from grazed areas had significantly greater K and Na on clay exchange sites than soil from excluded areas possibly because of supplementation with salt blocks. A seasonal reciprocal relationship occurred for the proportional content of K and Na on clay exchange sites and on resin capsules: Na highest during the cold season, and K highest in the plant senescent period. This relationship may be important in retaining K in soil during snowmelt. Surprisingly, the robust pools of extractable Ca, Mg, K, and Na, and their proportional content on the exchanger differed significantly with time. Overall, the data suggest that the present grazing management plan does not greatly impact nutrient availability.