New Zealand Soil Classification Research Articles

A soil spectral library of New Zealand

Diffuse reflectance spectroscopy, both in the visible and near-infrared (vis-NIR: 350–2500 nm) and the mid-infrared (MIR: 2500–25,000 nm) ranges, has been increasingly employed as an alternative to obtaining a multitude of soil information and data non-destructively, rapidly, and cost-effectively. Soil spectral libraries (SSLs) have been developed across the world to calibrate prediction models for rapid and non-destructive assessment of soils at local, regional, national and global scales. Several continental or national libraries exist, for example, vis-NIR SSL in Europe, Australia, Czech Republic, Denmark, France, China and Brazil, and MIR SSL in the U.S., Switzerland and Brazil. In this study, we document the development of a vis-NIR and MIR SSL of New Zealand based on legacy and modern samples that have been sieved to 2 mm and air-dried, and explore the application of such libraries for predicting a wide range of soil properties, including soil carbon (total carbon or organic carbon), total nitrogen, pH, soil texture (sand, silt and clay), phosphate retention and available water capacity (field capacity and permanent wilting point). The vis-NIR and MIR spectral features were compared between New Zealand Soil Classification (NZSC) soil orders and the performances of both vis-NIR and MIR SSLs were compared with other national SSLs. Results of the study indicate that both vis-NIR and MIR SSL demonstrated reliable modelling performance using the PLSR model. However, MIR outperforms vis-NIR for all soil attributes. Furthermore, the study found that both vis-NIR and MIR have the potential to distinguish different soil orders within the NZSC.

Cadmium accumulation in three contrasting New Zealand soils with the same phosphate fertilizer history

Cadmium (Cd) concentration in New Zealand (NZ) agricultural soils has increased due to phosphate fertilizer application, but it is not clear whether soils with different properties accumulate Cd at similar rates for given P loadings. Here, the distribution of Cd was measured in three soils: the well-drained Horotiu series (Orthic Allophanic Soil in NZ soil classification, Typic Hapludand in US soil taxonomy), poorly-drained Te Kowhai series (Orthic Gley Soil in NZ classification, Typic Humaquept in US soil taxonomy) and an intergrade between them, Bruntwood series (Impeded Allophanic Soil in NZ soil classification, Aquic Hapludand in US soil taxonomy). All three soils often occur in the same paddock with the same fertilizer history, but have differing drainage and mineralogical characteristics, permitting an assessment of the potential for varying accumulation/translocation of Cd in contrasting soil conditions. Thirty soil profiles from ten paddocks on a dairy farm near Hamilton, NZ, with a uniform fertilizer history were sampled to depth of 60cm. The Cd concentration in topsoil (0–7.5cm) samples (mean of 0.79mgkg−1) was about 7–8 times greater than in deeper horizons (P<0.001). No significant differences in Cd concentration or fractionation among the soil series were detected. Cluster analysis showed that Cd, phosphorus (P) and uranium (U) were highly correlated, consistent with a common source, most likely phosphate fertilizer. The absence of a difference in the Cd depth profiles in the three soils indicates that Cd was preferentially adsorbed to the topsoil and was not significantly mobilized by drainage in the soils. The lack of difference in Cd distribution between contrasting soil series supports the use of one Cd management system tool for all of these soils.