Spatial variability in topsoil micronutrient contents in a one‐hectare cropland plot

Abstract

Abstract The spatial variability of meso‐ (Ca and Mg) and micronutrients (Fe, Mn, Cu, Zn, and Co) was investigated in a small cultivated plot (1.8 ha) located in the Ordenes Complex, a district of basic schists in northwest Spain. The topsoil was sampled according to a nested sampling pattern to describe the spatial variability by geostatistical techniques from 0 to about 120 m. At the sampled scale results showed that the determined meso‐ and micronutrients are spatially dependent; furthermore, pH, organic carbon, cation exchange capacity (CEC) and two texture fractions, namely sand and silt content, also present a distinct ordered spatial variation. The spatial structure of the studied nutrients was analyzed and variogram models with a nugget component and two spatial components with ranges of 20 and 50 m were found to fit the experimental results. Contour maps made by block kriging allowed to identify micro‐regions with significantly high or low extractable nutrient contents. Micronutrient distribution appear to depend largely on organic C content, soil texture, cation exchange capacity and pH. The number of samples required to assess a mean value for extractable nutrient content was calculated. Reasonably accurate determination (i.e., 95% confidence and 20% relative error) of mean nutrient contents in a plot of this size and characteristics requires 16 to 20 samples. To reduce error due to spatial dependence, samples should be about 20–25 m apart.