Urease activity in Argentine soils: Field studies and influence of sample treatmenT

The effects of various treatments and seasonal variation upon urease activity were studied on surface samples of Argentine agricultural soils. Samples were selected to be representative of the zone covering a wide range of chemical and physical soil properties. Five sample treatments were selected: moist fresh; moist stored; air-dried; refrigerated; and frozen. It was shown that storage of soil at 4°C in sealed plastic bags maintained the natural moisture content and resulted in urease values most closely to those obtained at the time of sampling. Three Typic Argiudols under different vegetation covers were selected to elucidate the seasonal variation of urease activity. The highest enzymatic activities were found during the summer, whereas lowest values were encountered during the winter. The gradients of urease activity were different for the two types of vegetation studied (forest and natural grassland). As the values of urease activity also presented differences between soils under the two types of vegetation it may be presumed that the activity of this enzyme is related to the type of vegetation.