Physicochemical properties of 50 New Zealand pasture soils: a starting point for assessing and managing soil microbial resources

New Zealand's pastoral agriculture faces challenges associated with increasing on-farm productivity, while minimizing the environmental footprint of farming. Soil microorganisms mediate a wide range of processes that affect plant production and also have environmental consequences. However, there has been little attempt to manage these in a farming system context. This is primarily because of difficulties in determining what microbiological resources are present in soils, how they link with soil processes and function, and how variation in soil types, climate or farm management practices influence microbial function. We sampled 50 pasture soils from across 11 of New Zealand's major soil groups, 10 geographical zones and under different grazing systems (high input dairy units to dry-stock grazing). The environmental and physicochemical properties of the soils were characterized and DNA extracted. The concentrations of elements primarily associated with fertilizer use (phosphorus, nitrogen and sulphur) were all significantly (P< 0.05) higher in dairy-based systems, yet soil carbon was unchanged. The concentration of many properties varied between the soil types, reflecting a combination of their pedogenesis and predominant land use. The amount of DNA in soils was closely related to anaerobically mineralizable nitrogen (P< 0.001), a measure of soil organic matter content, but did not vary with grazing system intensity. The extensive data set for each soil, coupled with DNA originating from the same samples, provides a unique opportunity for a number of ancillary studies to map biological resources in pastures and assess how these are regulated by edaphic and environmental properties.