Spatial heterogeneity within the plough layer: low and moderate variability of soil properties

The spatial heterogeneity of soil moisture, total pore space, water-filled pore space, pH, organic carbon (Corg), of microbial biomass-C (Cmic), basal respiration, metabolic quotient, Cmic-to-Corg ratio, dissolved organic carbon (DOC), DOC-to-Corg ratio, nitrate and ammonia content were examined on an arable soil developed from loess. Soil samples were taken at two depths (0-15 and 15-30 cm) of the whole plough layer at regular intervals (7 m) on a sampling grid (9 row x 9 columns) across a 0.38 ha field plot site (60 x 63 m). Two sampling times were selected, one before (March) and one after (May) a field experiment with three crops and three N fertilization rates was laid out on a uniformly-managed area. The effects of the experimental treatments on the spatial variability in the soil properties were investigated. The soil properties could be characterized according to the extent of their spatial heterogeneity within the whole plough layer. Spatial variability of soil moisture, total pore space, water-filled pore space, pH and Corg was low and characterized by coefficients of variation (CV) less than 10%. Their spatial variability was not influenced by the imposition of the experimental plots. These low spatial heterogeneities and their stability reflected the long history of land use for arabic purposes. Moderate spatial variability in the soil of Cmic, basal respiration, metabolic quotient, Cmic-to-Corg ratio, DOC, DOC-to-Corg ratio, and nitrate and ammonia content was found, characterized by CVs ranging between 16% and 44%. The experimental treatments had no measurable effect on the deeper part of the plough layer (15-30 cm). The change of soil management had a small effect on the surface layer (0-15 cm) within 2 months of imposition of the field plots. The changes were mainly due to the crop species grown. The moderate spatial variability reflected interactions between the soil physical, chemical and biological components and their relative stability during the period of investigation.