Spatial-temporal variability of soil moisture, nitrogen availability indices and other chemical properties in hoop pine (Araucaria cunninghamii) plantations of subtropical Australia

Abstract

The spatial variability of soil moisture, nitrogen (N) availability indices (total N, NO3−–N, NH4+–N, potential mineralizable N (PMN)), and other chemical properties (organic C (OC), available P, pH, CEC, exchangeable K, Ca, Mg, Mn, Na) was investigated in two plots (1.36 ha each) of eight-year-old hoop pine (Araucaria cunninghamii Ait. ex D. Don) progeny tests located in south-east Queensland, Australia, for dry and wet seasons. Following a nested sampling pattern, soil samples of 0–10 cm depth stratified at three different sampling scales (378, 42 and 2.6 m2) were taken. The hierarchical model of analysis of variance was used to analyse the spatial structure of these soil properties. The objectives of this study were to: (1) evaluate the spatial–temporal variability of soil properties in the two plots, and (2) develop an effective sampling strategy for similar test plots.

At the wet season in the study plot 1, it was shown that for soil total N, CEC, pH, exchangeable Ca, Mg, and Na there were significant differences between means of 42 m2 plots within 378 m2 plots and between those of 378 m2 plots within the 1.36 ha plot. For available P, PMN, mineral N, OC, and exchangeable Mn only differences between means of 42 m2 plots within 378 m2 plots were significant. For soil moisture, NH4+–N and exchangeable K there were significant differences between means of 378 m2 plots within the 1.36 ha plot. For all of these properties there were no significant differences between means of 2.6 m2 plots within 42 m2 plots, mainly due to substantial variation (30–70% of total variance) of the soil properties within 42 m2 plots. No spatial structure was found for soil NO3−–N. For the dry season in the study plot 1, the patterns of the spatial variability only for soil total N, mineral N and available P remained the same as for those of the wet season. For study plot 2 at the wet season, the patterns of spatial variability for such soil properties were less pronounced. The sampling strategy for evaluating tree productivity potential of the plots and for monitoring the soil properties was highly dependent on set of the properties chosen, and on expected changes in means of soil properties from date to date. The findings are discussed in relation to the issues concerning assessment of tree growth performance in forest plantations.