Minimum repeatability of laboratory tests to identify changes in the content of soil organic matter

The paper outlines the calculations for the minimum number of individual and combined samples required for control and inspector measures to detect a statistically significant change in the soil organic matter content, as determined according to GOST 26213-91 (the Tyurin's method). The threshold for this change is a decrease of the organic matter content in the arable soil layer by 15%. The paper also considers the impact of analytical error and spatial variation on the final result. Spatial variation was analyzed for sod-podzolic soils, southern chernozems, and ordinary chernozems. It was found that for low values of the substance content (up to 3%), the analytical repeatability should be at least n = 2. For higher values, the analytical repeatability may be reduced to a single sample. The number of individual samples needed to estimate the average organic matter content with a confidence level of 0.95 can vary widely, ranging from a few to several dozen, depending on the extent of spatial variation, which is characterized by the coefficient of variation. By combining samples, the number of analytical repetitions can be significantly reduced, but this approach also requires more careful consideration of mixing requirements. The primary samples must be of the same volume, and the mixing process must be carefully controlled to ensure uniformity.  

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