Thermal stability and activities of soil enzymes as influenced by crop rotations

Soil samples were collected to a depth of 10 cm in 1991 and 1993 from a vegetable crop rotation experiment initiated in 1989. The two cropping treatments, with either 0 or 280 kg N ha −1, represented the traditional vegetable rotation (TVR) and an alternative legume vegetable rotation (LVR) when a vegetable crop alternated with a red clover ( Trifolium pratense L.) seed-crop that was incorporated as green manure in the following spring. The enzyme activities of L-asparaginase, amidase and β-glucosidase were determined on whole soil and five soil aggregate size fractions: 1.00–2.00, 0.50–1.00, 0.25–0.50, 0.10–0.25 and