The activity of -glucosidase was determined as described previously
for phosphomonoesterase activity, with the modification
that the substrate was p-nitrophenyl--glucopyranoside and the
liberated p-nitrophenol was determined by THAM–NaOH (0.1 M,
pH 12; Eivazi and Tabatabai, 1988). Arylsulphatase activity was
determined with p-nitrophenyl sulphate as substrate, incubating
soils at pH 5.8 (acetate buffer 0.5 M) and 37 ◦C for 1 h (Tabatabai
and Bremner, 1970). For urease activity determination, we used
the Kandeler and Gerber (1988) method. After the addition of aqueous
(controls) or a buffered urea solution (samples) to 5 g of soils
samples, they were incubated for 2 h at 37 ◦C. Liberated ammonium
was extracted with potassium chloride solution after being
shaken for 30 min and filtered in order to prevent the interference
of possible precipitates. The method used to determine urease was
based on the reaction of sodium salicylate with NH3 in the presence
of sodium dichloroisocyanurate which forms a green-colored
complex under alkaline pH conditions, and the extinction was measured
at 690 nm.