Abstract
The frequency distributions of soil NO -3 and NH +4 concentrations under grazed and ungrazed grassland were found to be lognormal, irrespective of time of year or soil depth. The variance and skewness of the sample values increased with stocking density and use of N fertilizer. An analysis of the spatial dependence of the variability using the semivariogram showed a high ‘nugget’ variance, even when three sample values from each sampling point were averaged. Most of the variance was therefore short-range (occurring within a distance of 0.4 m), suggesting that the sample volume for soil mineral N measurement should be as large as is practicably possible. As an estimate of the average mineral N content, the geometric mean of the sample values consistently underestimated the true arithmetic mean of the population from which the same was drawn. The conventional estimate of the arithmetic mean for lognormally distributed samples values was satisfactory when the sample number was > 50 and the (log) variance < 0.75 (µg N cm−3). However, for data with larger variances, high coefficients of skewness and fewer observations, Sichel's estimator was a more efficient measure of the true population mean.
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White, R., Haigh, R.A. & Macduff, J. Frequency distributions and spatially dependent variability of ammonium and nitrate concentrations in soil under grazed and ungrazed grassland. Fertilizer Research 11, 193–208 (1987). https://doi.org/10.1007/BF01063317
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DOI: https://doi.org/10.1007/BF01063317