Studies on urea hydrolysis in salt affected soils

Abstract

In laboratory incubation studies, the kinetics of urea hydrolysis was analysed in seven soils widely differing in salinity and sodicity. The effects of the kind of salinity on urea hydrolysis was studied in a non-saline Tulewal Sl soil treated with solutions (100 me/1 to produce ECe values of approximately 10 m mhos/cm) of NaCl, NaSO4, NaHCO3 or NaCl + CaCl2 salts. In another experiment the rates of urea hydrolysis in the soil samples collected from two recently reclaimed salt affected areas were also studied. The results showed considerable variations in the rates of urea hydrolysis in different soils. Urea hydrolysis was considerably delayed with increase in soil pH. The time required for complete hydrolysis to occur varied from 3 to 14 days. Urea hydrolysis seemed to follow first order reaction kinetics. The average time for one half of the hydrolysis to occur (t1/2) ranged from 0.51 yo 4.55 days. The delay in urea hydrolysis was related to decrease in urease activity with increase in pH, decrease in organic matter (and total N). The Na HCO3 treatment decreased the activity of urease and hence resulted in the maximum delay in urea hydrolysis followed by NaCl and Na2SO4 salts in the ascending order. Urea hydrolysis was faster in recently reclaimed sodic soils than in unreclaimed soils.