Influence of chemical properties on nitrogen mineralization and nitrification in podzolized sands. Implications for forest management

Abstract

The relationship between selected chemical properties and nitrogen mineralization and nitrification was examined in soils collected from 39 sites of varying history. All sites were on podzolized sands; such soils represent more than 95% of the P. radiata growing area in south-east of South Australia/western Victoria. Given their uniformity in texture and similarity in pedogenesis, the organic matter concentrations of the sampled soils were highly variable (loss-on-ignition 0.8-10.2%). Total nitrogen was highly correlated with loss-on-ignition (r2 = 0.95, P<0.001). Nitrogen mineralization was correlated neither with total nitrogen nor loss-on-ignitition (i.e. P > 0.05), but was correlated with organic phosphorus (r2 = 0 70, P < 0.001), suggesting a major effect of phosphorus on nitrogen mineralization in these soils. On the basis of nitrate production during a 56-day aerobic incubation of disturbed soil, 18 soils were classed as strongly nitrifying (having a high potential to nitrify) and 18 as weakly nitrifying (having a low potential to nitrify). This separation reflected differences in other soil properties, with discriminant analysis giving a 91.7% correct classification into the two groups using only pH and Bray (II) extractable phosphorus for discrimination. Strongly and weakly nitrifying groups could also be discriminated on the basis of their value/chroma rating (after ignition), with a 94.4% probability of correct classification. Within each classification, nitrogen mineralization was correlated with total nitrogen (r2 =0.59 and 0.65, P< 0.001, for strongly and weakly nitrifying soils, respectively) but with a different relationship in each case. The significance of this difference in nitrogen dynamics is discussed in relation to site-specific forest management practices.