A survey of urease activity in soils of Northern New South Wales

Abstract

The hydrolysis of urea to ammonia is an important pathway of conversion of organic nitrogen to inorganic nitrogen in solls receiving applications of urea 9 and excretions of urine from stock 6. Conrad 8 4 hypSthesised that urea hydrolysis could be catalysed by extracelhflar urease adsorbed in soils, a process quite independent of the catalytic action initiated by viable urease-containing soil micro-organisms. Since then the activity of this enzyme in soils has been examined both as a separate enzyme system 2 14 15 23 and as orte of a number of enzymes in broader studies of the total enzyme activity s 12 la It would appear that urease in soil is found within the eells of metabolizing ureolytic micro-organisms and plant organs, and as an extracellular portion derived from ruptured, moribund cells. Since extracellular urease is adsorbed on clay particles and humified organic marter 4 iß 19 23, soils exhibit levels of urease activity which are not necessarily directly related to the numbers, weights or activity of the viable ureolytic organisms at the time of determination of the urease activity la. Nevertheless, factors influencing the ureolytic population and the production of urease from this source, as well as factors influencing the aetivity and preservation of the enzyme itself, taust together determine the urease activity of a soil.It should be noted that in conformity with other workers 12 la 14 23 the term urease activity as used herein without qualification refers principally to the activity of extracellular urease in the soil, and excludes the urease activity of metabolizing ureolytic micro-organisms. This definition accepts the premises that in the method

Ammonia losses from surface-applied urea as related to urea application rates, plant residue and calcium chloride addition

“…Burns et al [2] and Zantua and Bremner [17] found that urease activity in a soil was maintained even under anaerobic environments, high temperatures and sterile conditions. The site of urease activity has been correlated to both clay particles and soil OM [9,10,12,13,14,16]. Persistence of urease may be due to association with lignaceous organic materials and/or entrapment by clay particles which prevent decomposition and entry of microorganisms, respectively.…”

Effect of Application of Liquid Swine Manure on Soil Organic Carbon and Enzyme Activities in Two Contrasting Saskatchewan Soils

“…Conversely, Burns (1978) has reported that on soil samples collected on five separate occasions over a period of three years from the same location, urease activity remained the same, independent of season. McGarity and Myers (1967) reported that on soil samples collected from winter to late spring period, there were no major differences in urease activities. However, only a few studies have looked at enzyme activity in soils with several years' history of manure application (Eivazi et al, 2003;Lalande et al, 2000).…”

Atributos bioquímicos e químicos do solo rizosférico e não rizosférico de culturas em rotação no sistema de semeadura direta

“…A urease foi determinada como proposto por McGarity & Myers (1967), realizando-se a incubação das amostras de solo por 3 h, a 37 °C, utilizando-se ureia 1 % como substrato, seguida de centrifugação e determinação. Os resultados foram calculados a partir de uma curva-padrão com solução de sulfato de amônio e expressos em μg N-NH 4 g -1 solo 3 h -1 .…”