HDLN Soil and Water Dairy Action Program - Soil Characterisation

Project Introduction

Through the use of selected soil physical and chemical properties, and visual assessment of soil structure and biota in the field this project aimed to benchmark the soil health of dairy farms in the In this research project, we aimed to benchmark the soil health on dairy farms in the Curdies River catchment. Emphasis was placed on the Scott’s Creek/Cooriemungle sub-catchments.

A total of 24 properties were sampled between 2005 and 2007. These farms represented the major landscape components in the catchment. On each of these farms, three paddocks, 2–3 sites within each of 3 paddocks were chosen for monitoring.


Methodology

During late October and early November 2005, intact soil cores were taken from each of the 30 monitor paddocks. Ten cores were taken along a transect at 10 m intervals, resulting in a total of 300 intact cores. The cores were taken in the field by first removing the pasture mat and then driving a PVC pipe (5 cm high and 7 cm diameter) into the ground.

During mid December 2005 to early January 2006, the 30 monitor paddocks were sampled for nutrient status of the surface soil (i.e. 0–10 cm). Paddocks were sampled in 2–3 strata in order to gain an understanding of where high and low nutrient values occur within a paddock. When dividing a paddock for sampling, factors such as animal movement within the paddock, variation in topography, vegetation and obvious drainage lines were taken into consideration. Samples from each strata of the paddock consisted of 30–40 sub-samples taken with a foot sampler. One to 2 hand-auger holes were made in each paddock to get some idea of depth to subsoil.

In October 2006 and 2007, 2–3 monitoring sites (10 m by 10 m) per paddock were selected to cover the range of expected soil physical conditions e.g low-lying vs. well-drained areas, high stock density vs. low stock density). In October 2006 and 2007, 30 sub-samples were taken with a foot sampler, from the same 10 m by 10 m monitoring sites used for the soil physical analyses. In the middle of each monitoring sites, a hand-augered hole to about 1m deep was used to give a full description of the soil profile.

For the intact cores, three 30 cm square quadrants were randomly located within the monitoring site. The intact soil core was collected using a single brass cylinder (73 mm diameter and 47 mm high).

The soil samples were analysed for pH in water and 0.01 M CaCl₂, electrical conductivity (EC) (1:5 soil:water), total nitrogen (N), Olsen phosphorus (P), Skene potassium (K), CPC sulphur (S), total carbon (C), and exchangeable aluminium (Al), calcium (Ca), magnesium (Mg), potassium (K) and sodium (Na). Exchangeable acidity was also measured in 2005 only, while phosphorus buffering index was included in 2006 and 2007. Laboratory analyses also included physical tests such as slaking, dispersion and field texture.

Analyses undertaken were: volumetric soil water content as received, volumetric soil water content at 0 kPa, 1 kPa and 10 kPa tensions, bulk density, and air-filled porosity at 10 kPa tension.


Soil Health Benchmarks

Benchmarks for the main soil health parameters tested are suggested in Table 1, to assist farmers and service providers relate technical data to soil health.