Significance of gravimetric versus volumetric measurements of soil quality under biodynamic, conventional, and continuous grass management

ABSTRACT:

We analyzed 22 physical, biological, and chemical soil properties using adjacent fields from commercial farms in New Zealand. Our objective was to measure the effects of biodynamic, conventional, and continuous grass systems on soil quality. One set of three adjacent farm fields included a biodynamic vegetable field, a conventional vegetable field, and a biodynamic pasture field. A second set of three adjacent farm fields included a biodynamic mixed (grain/sheep/beef) field, a conventional mixed field, and a biodynamic pasture field. The pasture fields had soils of higher biological quality (i.e., more organic matter, microbial activity, and earthworms) than the soils of the biodynamically or conventionally cropped fields. The biodynamic vegetable field had soil of higher physical, biological, and chemical quality than its conventional neighbor. When converting the chemical and biological data from a mass to a volume basis, most statistically significant differences remained in the vegetable/pasture data set, whereas many became nonsignificant in the mixed/pasture data set. Presenting data on a volume basis per unit given surface depth (like 0 to 10 cm in this study) may penalize a farm with lower bulk densities and thicker topsoils in comparison to an adjacent farm with higher bulk densities and thinner topsoils. We recommend calculating soil measurements on a volume basis per unit of top-soil depth (comphte A horizon) or per unit of solum depth (A and B horizons). Whether data are presented on a mass or volume basis, biological or ecological significance should be emphasized rather than statistical significance.