The effect of rock content on nutrients in a Sierra Nevada forest soil
2012
Johnson, D.W. | Walker, R.F. | Glass, D.W. | Miller, W.W. | Murphy, J.D. | Stein, C.M.
The effects of rock content on nutrient concentrations and contents (kgha⁻¹) in a skeletal soil derived from andesite were investigated. Rock content to a 60cm depth ranged from 8 to 69% among 20 quantitative soil pits within a 10ha area. On average, rocks contained 9% of total soil C, 19% of total soil N, 3% of total ecosystem C, and 12% of total ecosystem N. Percent rock content also appeared to cause increases in organic matter concentrations: rock content was significantly, positively correlated with total C and total N concentrations in the fine earth (>2mm) fraction. Soil C was organic; no carbonates were present. Percent rock content was also significantly, positively correlated with fine earth C:N ratio, suggesting that organic matter in rockier soils was in an earlier stage of decomposition at any given depth. Other consistent correlations with rock content included Bray P (positive) and exchangeable Mg²⁺ (negative). The decrease in fine earth mass with increasing percent rock content offsets the increase in C concentration such that there was no correlation between percent rock content and either fine earth or total soil (fine earth plus rock) C content (kgha⁻¹). Percent rock content was significantly negatively correlated with total N, Bray P, inorganic N, exchangeable K⁺, Ca²⁺, and Mg²⁺ contents, however. The results of this study show that high rock content can affect soil C and nutrient pools not only because of the contributions of the rocks themselves, but also because high rock content appears to cause higher concentrations in the fine earth fraction.
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