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).
Green shaded columns indicate soil quality target ranges, follow the referenced links for more information.
Target range is ‘Depleted’ to ‘Ample’ (modified from Hill and Sparling 2009 to have no upper bound on the ample category). *Organic soils excluded as by definition these soils have ample total carbon content.
Target range is ‘Depleted’ to ‘Ample’, (Hill and Sparling 2009). *Cropping and horticulture excluded as ranges would depend on specific crops grown.
Target range is ‘Slighly-acidic’ to ‘Optimal’ (Hill and Sparling 2009). Note that we refer to their ‘Sub-optimal’ rating as ‘Slightly alkaline’ throughout this report. Also note that soil pH classifications differ from usual liquid pH classifications; liquid acidity and alkalinity are usually classified with respect to a neutral pH of 7, whereas soil acidity and alkalinity are classified relative the optimal range for that land use and soil order.
*Forestry on organic soils are excluded as this combination is unlikely in real life due to windthrow.
Target ranges are set for different land use and soil orders (McKay et al 2013). Note that ‘Market gardening’ refers to the cropping of Celery, Leeks, Winter Lettuce, Onions, Early Potatoes, and Winter Spinach. Note also that lifestyle blocks are included in ‘Pastures, [other] cropping, and horticulture’.
Target range is less than the soil guideline value (Cavanagh 2019). Note: Other values may apply for non-agricultural land uses, soils and circumstances.
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.
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.