Changes in Nutrient Distribution in Forests and Soils of Walker Branch Watershed, Tennessee, over an Eleven-Year Period

• Published in: Biogeochemistry 1988-10, Vol.5 (3), p.275-293
• Main Authors: Johnson, Dale W., Henderson, Gray S., Todd, Donald E.
• Format: Article
• Language: English
• Subjects: Acid soils; Agronomy. Soil science and plant productions; Biological and medical sciences; Chemical bases; Forest ecosystems; Forest litter; Forest soils; Fundamental and applied biological sciences. Psychology; General agronomy. Plant production; Soil ecology; Soil horizons; Soil nutrients; Soil-plant relationships. Soil fertility; Soil-plant relationships. Soil fertility. Fertilization. Amendments; Subsoil; Vegetation
• ISSN: 0168-2563; 1573-515X
• DOI: 10.1007/BF02180068

Changes in vegetation, litter, and soil nutrient content were measured in selected plots on Walker Branch watershed, Tennessee, from 1972-73 to 1982. The watershed has been allowed to revert to forest since 1942, before which it consisted of small subsistence farms and woodland pastures. Changes in Ca status were of particular interest because initial nutrient cycling characterizations indicated that net Ca accumulation in vegetation could have caused large decreases in soil exchangeable Ca2+ within 20 years. Decreases in forest floor and subsoil (45-60 cm) N, exchangeable Ca2+, and Mg2+ content were noted in several plots from 1972 to 1982. Surface soils (0-15 cm) showed either no change or, in some cases (e.g., N and exchangeable K+ in certain plots), increases over the 11-year period. Reductions in forest floor and subsoil exchangeable Ca2+ and exchangeable Mg2+ on cherty, upper slope oak-hickory and chestnut oak forests were most striking. The changes in Ca2+ are thought to be due primarily to high rates of Ca incorporation into woody tissues of oak and hickory species. Reductions in forest floor and subsoil exchangeable Mg2+ could not be accounted for by woody increment; leaching may have played a major role in causing these decreases. Changes in P and exchangeable K+ were variable, with both increases and decreases. There were significant increases in exchangeable Al3+ in both subsoils and surface soils of certain plots, but these were not accompanied by decreases in exchangeable base cations or consistent decreases in pH. Dissolution of interlayer Al from 2:1 clays may be the cause of the exchangeable Al3+ increases. These results suggest a general decline in fertility, especially with regard to Ca and Mg in those forests with low soil Ca and Mg supplies. Monitoring of further changes (if any) in these ecosystems will continue as the currently aggrading forests approach steady state.