Daintree Rainforest, Cape Tribulation Soil Characteristic Data 2006 - 2015

The collection of physico-chemical characteristics of soil from the Daintree Rainforest, Cape Tribulation site was conducted between 2006 and 2015. In 2006, a pit was dug and soil samples were collected from the face of the pit for each layer :0.0-0.1 m, 0.1-0.2 m, 0.2-0.4 m, 0.4-0.6 m, 0.6-0.8 m, 1.45-1.55 m. Samples were air-dried to constant mass, sieved to 2 mm, roots and rocks removed and weighed. The samples were homogenised and sent off for analysis within 5 days. Sieved (<2mm) samples were analysed, using methods described by Rayment and Higginson (1992) for exchangeable Ca, Mg, K and Na (Method 15A1), exchangeable acidity and Al (Method 15G1), Colwell extractible P (Method 9B2), total C (Method 6B4), total N (Method 7A7), electrical conductivity (EC) and pH (both in 1:5 soil:water extract) and particle size distribution. As the soil has a high content of stones, the volumetric proportion of soil and rock was determined at several depths. The total volume of each depth increment was determined by pouring measured volumes of sand into a pit as it was excavated. The excavated soil was sieved (2 mm); and material passing through the sieve was called soil. Material that was retained on the sieve was mechanically tumbled for 45 minutes in order to break apart aggregates of soil and to separate soil from the rocks. The tumbled material was sieved again through a 2mm sieve and the material retained was separated into roots and rocks. All materials were weighed and the water content of the soil was determined. Using a calibrated 20L bucket, the volume of rocks (pre-wet to prevent loss of water by absorption) was measured. The volume of soil in each layer was calculated by subtracting rock volume from the volume of the excavated hole. A different soil pit was dug to 1.5 m depth in July 2007 and monitoring probes were installed at 0.1, 0.75 and 1.5 m depths in three columns. At each depth there were 3 time domain reflectometry probes (Campbell Scientific CS616) to measure volumetric water content, 3 gypsum blocks (Measurement Engineering Australia GBHeavy, except at 0.1 m depth were there were only 2) to measure water potential over the range -30 to -600 kPa. In addition one TCAV thermocouple probe to record soil temperature was located in the centre of the soil pit at 0.10m. In each column the time domain reflectometry and gypsum blocks were separated laterally by 20cm, each column was separated from the next by 100cm. At each depth the time domain reflectometry and gypsum blocks were separated laterally by 1 m. Sensors were installed in layers maintaining the vertical configuration of 3 columns. The pit was backfilled by hand, layer by layer, to the original bulk density. Sieved soil was packed around each probe to ensure good contact and a layer of rock-free soil of at least 3 cm around the sensors.