Relationships between soil porosity, root development and soil enzyme activity in cultivated soils

Porosity and pore size distribution from thin sections, prepared from undisturbed Ap horizon sam- ples taken from a zero- versus conventional-tillage field experiment, were analysed by means of a Quantimet 720 image analysing computer. The length and the size distribution of plant roots were determined using the same image analyzer. Soil urease and phosphatase activity in soil samples from the plots of this field experiment was also determined. Total porosity was significantly higher in conventionally tilled plots, but the proportion of pores ranging from 30 to 500 μπ\ in equivalent pore diameter, which are considered the most important both in soil-water-plant relationships and in the maintenance of a good soil structure, was higher in no-tilled plots. Root development showed a strict relationship with the presence of smaller pores which were more numerous in no-tilled plots. Enzyme activity was also higher in these plots than in the conventionally tilled plots. The relationships of such enzyme activities and the various pore size classes in each type of soil showed a positive common trend between the two enzyme activities and the percentage area of pores ranging from 30 to 200 μτη in equivalent pore diameter. A significant correlation was observed be- tween the degree of porosity in this range and urease activity.