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 (C-org), of microbial biomass-C (C-mic), bas al respiration, metabolic quotient, C-mic-to-C-org ratio, dissolved organic carbon (DOC), DOC-to-C-org ratio, nitrate and ammonia content were examine d on an arable soil developed from loess. Soil samples were taken at two de pths (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 a fter (May) a field experiment with three crops and three N fertilization ra tes was laid out on a uniformly-managed area. The effects of the experiment al treatments on the spatial variability in the soil properties were invest igated. The soil properties could be characterized according to the extent of their spatial heterogeneity within the whole plough layer. Spatial varia bility of soil moisture, total pore space, water-filled pore space, pH and C-org 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 arable purposes. Moderate spatia l variability in the soil of C-mic, basal respiration, metabolic quotient, C-mic-to-C-org ratio, DOC, DOC-to-C-org ratio, and nitrate and ammonia cont ent was found, characterized by CVs ranging between 16% and 44%. The experi mental 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. T he 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 inv estigation. (C) 1998 Elsevier Science Ltd. All rights reserved.