Variability of topsoil properties at the southern coast of Finland and the number of  soil samples needed for the estimation of soil properties

A total of 430 topsoil samples were collected from ten fields of the Viikki Experimental Farm, University of Helsinki. Particle size distribution, organic carbon content, pH(CaCl2), exchangeable Ca, Mg, K contents, plant available P (Bray 1), 1 M KCI extractable (Al+H) content and effective cation exhange capacity of the soils were determined. The coefficient of variation was used as indicator of the variability of soil properties with in each field. The lowest coefficients of variation were observed for pH(CaCl2) and the highest for exchangeable Mg 1 M KCI extractable (Al+H) and effective cation exchange capasity. The results indicate that from 1 (pH(CaCl2)) to 33 (exchangeable Mg) samples per hectare are needed from individual fields for strict level of accuracy in estimation of the soil properties. For determination of soil type (according to clay content) and organic carbon content on average 8 samples, and for the plant available P (Bray 1) and exchangeable Mg and K contents 10 to 16 samples per hectare appear sufficient. Four samples suffice for a less stringent, lax accurate determination of all properties. The variability of soil properties is discussed from the viewpoint of agricultural advisory work and field experiments for agricultural research