Corangamite Soil Health Monitoring Program Data

Brief description

A set of 100 soil health monitoring sites from across the Corangamite CMA region of Victoria. Two rounds of soil test analysis have been performed at each of the sites (in 2014 and 2018). Analysis of samples from 3 depths (0-10cm, 10-20cm and 20-30cm) taken in a paddock transect and bulked. One core sample also taken for each site.

Generally, observations were made according to the conventions of Northcote (1979), Turvey (1987) and McDonald et al. (1990).

Data includes pH, texture, bulk density EC, nutrients (P,K,N,S), exchangeable cations, trace elements and Carbon fractions (Mid infrared - MIR corrected)

Full description

Both 2014 and 2018 nutrient analysis was performed by CSBP laboratory (Perth, WA). The tests involved pH (water), pH (CaCl2), Electrical Conductivity, Organic Carbon (Walkley Black), Cowell Phosphorus, Olsen Phosphorus, Cowell Potassium, Sulphur (KCl 40), and Exchangeable cations without pre-wash (Calcium, Magnesium, Sodium, Potassium, Aluminium) using Rayment and Lyons Method 15 E1.

In preparation of measuring fractionated carbon, three 67 mm diameter cores were taken to measure bulk density dispersed along the transect for the calculation of tonnes of carbon per hectare at approximately 30 m, 75 m, 120m. Samples were oven dried at 105oC for 24 hours to eliminate all moisture. Dry weights were taken and the following formula used to calculate bulk density. Bulk density (g/cm3) = Whole dry soil mass ÷ core volume. Bulk density was also calculated via the total weight of soil cores collected as a backup measurement which had been used in the Soil Carbon Research Program (SCaRP) for carbon measurement across Victoria. Samples were sent to Dr Jeff Baldock at the CSIRO laboratory in Glen Osmond, SA.

The samples were analysed for fractionated carbon and nitrogen using the Leco dry combustion method. Only the carbon levels are reported in this paper. Samples were prepared following the National soil carbon research programme: field and laboratory methodologies 2011. Calcareous samples containing inorganic carbon were determined and used to correct Leco values. Carbon amounts (t/ha) were calculated from the Leco measured organic carbon (mg/g) which was corrected for gravel weight per sample greater than 2mm and multiplied by bulk density for each 10 cm soil layer. In 2014, two deep (100 cm) cores were taken and described using standard terminology to provide a full profile description by DPI Victoria. Soil pH field and CaCl2, EC were also measured. The cores and CSMP were used to help validate Nathan Robinson, DPI PHd project on Assessing productive soil and landscapes using digital soil mapping. David Rees and Michelle Davey created an information sheet for each soil core.

Lineage

The CSMP sampled 101 sites in the Corangamite catchment in 2014 and again approximately 4 years later in 2018. Sampling occurred across grazing and cropping paddocks over a range of soil types and agricultural uses including beef/sheep, dairy, mixed farming and continuous cropping (paddock cropped for greater than 10 years). Cores 10-15 were collected in a linear transect across 100 to 150 m, with sampling occurring every 10 metres. Differential Global Positioning System readings were taken of the 2014 transect, so that in 2018, sampling could occur from the same location. Each core was divided into three depths (0-10, 10-20 and 20-30 cm) and bulked together for testing. Cores 42 mm in diameter were used to provide enough soil for testing.

Sites were chosen by landcare groups that were representative of local soil types. Two sites that associated with the Geelong Landcare network fell outside the catchment near Little River. One stony rise site with id 101 contained much underground rock and so only a 10 cm sample could be obtained and not on a linear transect.

Sampling in 2014 occurred mainly in June/July and in April/May 2018. Ideally site sampling would be at the same time in autumn before sites become too wet and inaccessible. Differences in timing of sampling may provide an explanation for different results between sampling rounds. In 2014, SFS prepared the soil for testing. This involved oven drying samples at 40oC for 48 hours or until they had achieved a constant dry weight.

The samples were taken to Agriculture Victoria soil laboratory at Macleod were they were crushed to a 4-5mm size using a jaw crusher. Then the sample was put through a brush mill with a 2 mm sieve, so that the mineral soil was separated from larger gravel content and large organic matter. The gravel content was weighed which was later used as a correction factor in the calculation of tonnes of carbon/hectare.

Approximately each soil sample contained 2 to 3 kg of soil and in hindsight probably should have been subsampled and then put through the crusher. In 2018, whole samples were thoroughly mixed by hand and broken up using a hammer. This was difficult to achieve with some very hard subsoils. A 200g sub sample was sent to the CSBP soil laboratory where the samples were also air dried, crushed and sieved to the standard 2 mm. The slightly different soil preparation of 2-3 kg of soil mixed versus 200 g may contribute to some differences in samples especially heavy clay soils.

Funding Scheme