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



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(1) Soil chemical (carbon, nutrients, aluminum, exchangeable acidity, and pH) and physical (bulk density) properties were measured systematically every 40 m on two 12 ha watersheds in Puerto Rico before and after Hurricane Hugo. 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.

Date Range: 
1988-06-01 00:00:00 to 1990-07-01 00:00:00



Additional Project roles: 

Name: Miguel C Leon Role: Data Manager
Name: Arthur Johnson Role: Associated Researcher
Name: Frederick Scatena (In Memorium) Role: Associated Researcher
Name: Thomas Siccama Role: Associated Researcher


In 1988, prior to sampling, the watersheds were surveyed and permanently marked with stakes on a 40 m grid. A description was made of each grid point including information about tree species composition, basal area, and classification of the topography as either ridge, side slope, valley, or riparian valley (Scatena, 1989; Scatena et al., 1993) - See LTERDBAS #31: 40 X 40 grid vegetation and site characteristics, Bisley at In June 1988, forest floor and surface soils were sampled on Watersheds 1 and 2. Two 15 X 15 X 10 cm pits, one for chemistry and one for root and rock volume, were dug at each grid point, 1 m east and 1 m west of the stake. Pits were excavated by first securing a 15 X 15 cm template (insiude area) with long nails and removing all live vegetation. Forest floor material (composed of all recognizable dead plant material) was collected from within the sqaure and placed in a separate bag for processing. A 10 cm deep block of mineral soil was then carefully excavated and placed in a bag. Multiple soil samples from the 10-35 cm and 35-60 cm depths were collected from inside the excavated pit using a 2.5 cm diameter soil corer. At a few sites, it was not possible to collect samples from one or both of these lower horizons due to large rocks or roots.

To determine bulk density of the 10-35 cm and 35-60 cm depths, eight large quantitative pits (50 X 50 cm) were located in four elevation bands along the ridge dividing the two watersheds. Forest floor was removed and soils were excavated by depth (0-10 cm, 10-35 cm, 35-60 cm) using a technique outlined in Hamburg (1984). Soil from each depth of the big pits was weighed in the field using a spring balance and subsampled for dry weight conversions (105° C).

Fresh samples were stored in air-tight bags at approximately 4° C for less than one week prior to extractions and pH determinations. A subsample from all chemistry pits and the two lower depths from the 'roots and rocks pit' was given to the International Institute of Tropical Forest (IITF) in Puerto Rico. (For Lab and Statistical analyses methods see publication, Silver et al., 1994)



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