부산대학교 도서관

Purpose: A poor understanding of the nature of variation of soil properties within a field can lead to management decisions that reduce productivity or increase off-site environmental risks.Methods: The variability in total C%, total N%, plant-available (Colwell) P, and pH in CaCl2 at multiple depths is examined from two sites near Wagga Wagga and Yerong Creek in the mixed farming zone of southern New South Wales, Australia. The minimum number of cores required to estimate the mean for each soil property with a given level of precision (1%, 5%, and 10%) was determined and the distribution of the sample data was described by calculating the skewness and kurtosis.Results: The number of cores (42 mm diameter) required to estimate the mean was least for soil pH (3 cores) at both sites and greatest for Colwell P (25 and 58 cores) at a 10% precision in the surface 0.1 m of soil at the Wagga Wagga and Yerong Creek sites, respectively. The distributions of soil chemical properties were greatly varied with skewness and kurtosis both influencing the data. The mean value of the pH distributions sometimes exceeded the mode, leading to an underestimation of the extent of soil acidity. The mean value for Colwell P also often exceeded the mode, indicating an overestimate of the P status of the soil from a productivity perspective but concurrently underestimating the risk of off-site losses, associated with high P values at some locations. There was also an overestimation of the organic C fractions at these sites. Noteworthy in our data was a broad distribution across a large range in all soil parameters at the soil surface which, despite a generally normal distribution at that depth, gave a mean value that represents a relatively constrained approximation of the true fertility status of the soil.Conclusion: Thisstudy highlights the importance of understanding the nature of the variability in soil properties for interpreting soil test results appropriately for agronomic and environmental purposes. Due to its highly variable nature, Colwell P could not be reliably measured within the level of precision assumed under existing soil sampling guidelines used in Australia.