Analytical methods

Analyses of the soil chemistry and soil physics indicators were completed at the Landcare Research laboratory. Trace element analyses were undertaken at Hill Laboratories in Hamilton. Where necessary, samples were stored at 4°C until analysis.

Soil macroporosity was determined at the Landcare Research soil physics laboratory in Hamilton. The Land Monitoring Forum specifies that macroporosity should be measured at a matric potential of -10 kPa. Macroporosity is the percentage of pores > 30 microns in diameter, when measured at -10 kPa. Ambiguity may arise with other terms (e.g. air-filled porosity) or macroporosity measured at other matric potentials (Drewry et al. 2008; 2015).

Olsen P measurements analysed at Landcare Research were undertaken using a gravimetric (weight) method to avoid the influence of soil bulk density. In New Zealand several large commercial laboratories measure soil received in the laboratory by volume prior to Olsen P chemical extraction. The fertiliser industry guidelines for Olsen P measurement are based on a volumetric method. Further information and explanation is available from Drewry et al. (2013; 2015).


Benchmarking

Green shaded columns indicate soil quality target ranges, follow the referenced links for more information


Bulk density (t/m3)

Target range is ‘Loose’ to ‘Compact’ (Hill and Sparling, 2009).


Macroporosity (% v/v at -10kPa)

Target range is ‘Adequate’ (Hill and Sparling, 2009).


Total Carbon (% w/w)

Target range is ‘Depleted’ to ‘Ample’ (Hill and Sparling, 2009). *Organic soils excluded as by definition these soils have ample total Carbon content.


Total nitrogen (% w/w)

Target range is ‘Depleted’ to ‘Ample’, (Hill and Sparling, 2009). *Cropping and horticulture excluded as ranges would depend on specific crops grown.


Mineralisable nitrogen (mg/kg)

Target range is ‘Low’ to ‘High’ (Mackay et al. 2013).


Soil pH

Target range is ‘Slighly-acidic’ to ‘Optimal’ (Hill and Sparling, 2009). *Forestry on organic soils excluded as this combination is unlikely in real life due to windthrow.


Olsen P (mg/kg)

Target range is ‘Low’ to ‘Ample’ (Mackay et al. 2013). Notes: Sedimentary soil includes all other soil orders except Allophanic (volcanic ash), Pumice, Organic, and Recent (AgResearch classification sytstem).


Trace elements - draft eco-soil guidelines (mg/kg)

Target range is less than the soil guideline value (Cavanagh, 2019). Note: Other values may apply for non-agricultural land uses, soils and circumstances.


Trace elements - adapted from NZWWA (mg/kg)

Target range is less the the soil limit value (NZWWA, 2003). Note: the suggested values by Alloway (2008) suggested for copper deficiency (≤ 5 mg/kg) and zinc deficiency (≤ 10 mg/kg) may be of interest depending on circumstances and type of farm production.


Cadmium - Tiered Fertiliser Management System (mg/kg)

Target ranges depend on the choice and rate of phosphate fertiliser application, see the Fertiliser Association Tiered Fertiliser Management System for Soil Cadmium for more detail.