1. There is ample evidence that storage of moist soil below 4°C for days to a few weeks – or at freezing temperatures for longer periods – minimises biologically induced transformations in nutrient cations and anions. As air-drying brings soils towards a general equilibrium (Etchevers 1986), changes during storage, not due to contamination from the storage container, are likely to be small and slow.
2. Piper (1944) recommended crushing rather than grinding but accepted the need to grind heavy-clay soils. The New Zealand designed Rukuhia roller-mill, fitted with a stainless-steel screen (Waters and Sweetman 1955; Metson 1961), is locally popular but performs poorly on many hard-setting Australian soils. Consequently, corn-crackers and stainless steel hammer mills have been successfully adapted for such soils. These mills are efficient, although they have the potential to artificially increase the surface area exposed to subsequent chemical reactions (Etchevers 1986). Unlike the Rukuhia soil grinder, grinding and hammer mills require prior removal of gravels and concretions.