TOWARDS A BIOCHEMICAL QUALITY INDEX FOR SOILS - AN EXPRESSION RELATING SEVERAL BIOLOGICAL AND BIOCHEMICAL-PROPERTIES

Soil biological and biochemical properties are highly sensitive to env ironmental stress and thus can be used to assess quality. Any soil qua lity 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 prop erties. Many authors recommend the use of a native soil supporting cli max vegetation that has undergone minimal anthropogenic disturbance as a high quality reference soil. In this study which examined three suc h native soils of Galicia (N.W. Spain) bearing Atlantic oak-wood as th e climax vegetation, biological and biochemical properties were found to vary widely seasonally and with samplmg site and depth. These varia tions were closely correlated with the total carbon (C) and/or total n itrogen (N) contents of the soils. The following equation: Total N=(0. 38x10(-3)) microbial biomass C +(1.4x10(-3)) mineralized N +(13.6x10(- 3)) phosphomonoesterase +(8.9x10(-3)) beta-glucosidase+(1.6x10(-3)) ur ease explained 97% of the variance in total N for the soils studied, s uggesting that a balance exists between the organic matter content of a soil and its biological and biochemical properties. A simplified exp ression of the above equation may be useful as a biochemical quality i ndex for soils.