Biochemical properties of soils under crop rotation

Although biochemical properties are commonly used to study soil degradation brought about by agricultural practices, the data obtained are often not comparable because only small numbers of soils and biochemical properties are analysed. The biochemical status of 45 cultivated soils (cropped soils) in Galicia (NW Spain) under rotation of maize, rape and potatoes was evaluated by characterising a large number of biochemical properties, and the results were compared with those from soils under oak forest (climax soils), i.e., natural soils of the highest possible quality. The organic matter content of the cropped soils and the values of the biochemical properties analysed were much lower than those corresponding to the climax soils. However, when the biochemical properties were expressed per unit of organic C, the values for both types of soils were very similar, and for some properties the values for the cultivated soils were even higher. The different biochemical properties in the cultivated soils were largely unrelated to each other and to the organic matter content. The results indicate that intensive crop rotation has led to the loss of a large portion of the labile organic matter and suggest that the residual organic matter acts to stabilize hydrolytic enzyme activities. The stabilizing action implies a saving in enzyme synthesis and to a certain extent should mitigate the biochemical degradation associated with the loss of soil organic matter.