Patterns in soil and physical properties of the Bisley Watersheds 1 and 2 (Big Dig 1988, Big Dig 1990)

(1) Exchangeable cation concentrations were measured using different soil extracting procedures (fresh soil and air-dried and ground soil) to establish a range of nutrient availability in the soil, and to determine the relationship between different, but commonly used laboratory protocols.(2) Soils extracted using fresh soils generally yielded significantly lower exchangeable Ca , Mg, and K concentrations than soils which were dried and ground prior to extraction. Soil nutrients generally decreased with depth in the soil.(3) Several soil properties varied predictably across the landscape and could be viewed in the context of a simple catena model. In the surface soils, exchangeable base cation concentrations and pH decreased along a gradient from ridge tops to riparian valleys, while soil organic matter, exchangeable Fe and acidity increased along this gradient. On the ridges, N,P, and K were positively correlated with soil organic matter; on slopes, N and P were positively correlated with organic matter, and Ca, Kg, and pH were negatively correlated with exchangeable Fe. (4) Soil nutrient availability in the upper catena appears to be primarily controlled by biotic processes, particularly the accumulation of organic matter. Periodic flooding and impeded drainage in the lower catena resulted in a more heterogeneous environment. Drying and grinding the soil prior to extraction had a greater impact on exchangeable cations from the upper catena than in the valley positions, probably due to greater soil organic matter content. See Silver, W.L., F.N. Scatena, A.H. Johnson, T.G. Siccama, and M.J. Sanchez. 1994. Nutrient availability in a montane wet tropical forest in Puerto Rico: spatial patterns and methodological considerations. Plant and Soil 164:129-145. Support for this work was provided by grants BSR-8811902, DEB-9411973, DEB-9705814 , DEB-0080538, DEB-0218039 , DEB-0620910 , DEB-1239764, DEB-1546686, and DEB-1831952 from the National Science Foundation to the University of Puerto Rico as part of the Luquillo Long-Term Ecological Research Program. Additional support provided by the University of Puerto Rico and the International Institute of Tropical Forestry, USDA Forest Service.