The effect of soil pH and high urea concentrations on urease activity in soil

Abstract

The rate of hydrolysis of urea in soil over the wide range of concentrations, up to 10 moles N per dm3 soil solution, found in fertilizer practice, was examined in Begbroke sandy loam adjusted to different p H values.On rewetting air-dry soil, urease activity increased rapidly, reached a maximum within the first 24 h and then decreased slowly to level off after about 4 days. Pretreatment of the soil with urea or ammonium had n o effect on the urease activity. Urease activity increased with substrate concentration, reached an optimum value and then decreased with rising urea concentration. The results could be explained by substrate inhibition at higher urea concentrations, and the data are well described by a modified Michaelis-Menten equation involving three parameters, V,,,, K , and Ki where Ki is an inhibition constant. K , decreased linearily with rise in pH whereas Ki increased slightly between pH 4.9 and 7.0 and steeply between 7.0 and 8.4. V,,, increased with rise in pH, reached a maximum value a t pH 6.0 and then declined a t higher pHs.There was a further reaction, reaching a maximum rate at a urea concentration of about 0.2 molar N in the soil solution, that followed Michaelis-Menten kinetics. K, for this high affinity reaction increased up to pH 7.2 and then decreased a t higher pH values; V,,, increased up to pH 6.8 and then decreased. The contribution of the high affinity reaction was small except at low concentrations of urea.

Urease activity and urea hydrolysis rate under coupling effects of moisture content, temperature, and nitrogen application rate

“…Hydrolysis rate ( / U t ∂ ∂ ) increases first and then decreases with the increase in urea concentration [23] , which is different from this study's result. This study showed that hydrolysis rate ( / U t ∂ ∂ ) enhanced with the increase in urea concentration.…”

“…Singh's report [23] , the moisture content was 50% and nitrogen application rate was less than 200 mg/kg. However, the moisture content was between 19.2% (60% of field capacities) and 32% (100% of field capacities) and nitrogen application rate was between 247 mg/kg and 433 mg/kg in this study.…”

“…A significant negative correlation also exists between the nitrogen application and hydrolysis rate [22] . This relationship is due to the non-competitive substrate inhibition of urease and the inactivation of urease [13,23] . However, traditional Arrhenius model and first-order kinetic model did not consider the effects of moisture content and nitrogen application rate on K u .…”

Produtividade da cana-de-açúcar relacionada à localização de adubos nitrogenados aplicados sobre os resíduos culturais em canavial sem queima

“…Santos et al (1991) observaram aumento na taxa de hidrólise da U com o incremento na concentração do fertilizante, porém não proporcional às doses avaliadas. Nessa reação, há consumo de H + do meio, elevando, conseqüentemente, o pH, o que favorece a volatilização de NH 3 , principalmente com o aumento das doses de U (Singh & Nye, 1984;Kiehl, 1989). As menores perdas por volatilização ocorreram nas fontes NA e SA (Quadro 1).…”

Effective Use of Plant-Derived Urease in the Field of Geoenvironmental/ Geotechnical Engineering

“…The rate of hydrolysis of urea is increased with an increase in urea concentrations until a maximum is reached, beyond which hydrolysis is decreased. The results can be explained by substrate inhibition at higher urea concentrations [43,44]. Pervin et al has also studied the effect of various metal ions and chemicals on the activity of chickpea urease.…”