Towards a biochemical quality index for soils: An expression relating several biological and biochemical properties

Soil biological and biochemical properties are highly sensitive to environmental stress and thus can be used to assess quality. Any soil quality index should include several biological and biochemical variables so as to reflect better the complex processes affecting soil quality and to compensate for the wide variations occurring in individual properties. Many authors recommend the use of a native soil supporting climax vegetation that has undergone minimal anthropogenic disturbance as a high quality reference soil. In this study which examined three such native soils of Galicia (N.W. Spain) beating Atlantic oakwood as the climax vegetation, biological and biochemical properties were found to vary widely seasonally and with sampling site and depth. These variations were closely correlated with the total carbon (C) and/or total nitrogen (N) contents of the soils. The following equation: Total N = (0.38 x 10-3) microbial biomass C + (1.4 x 10-3) mineralized N + (13.6 x 10-3) phosphomonoesterase + (8.9 x 10-3) β-glucosidase + (1.6 x 10-3) urease explained 97% of the variance in total N for the soils studied, suggesting that a balance exists between the organic matter content of a soil and its biological and biochemical properties. A simplified expression of the above equation may be useful as a biochemical quality index for soils.