Effect of substrate concentrations, temperature and cropping system onhydrolysis of urea in soils
2004
Hamid, M. | Khalil-ur-Rahman | Sheikh, M.A.,University of Agriculture,Faisalabad (Pakistan). Dept. of Chemistry
The effect of substrate concentrations, temperature and cropping system onhydrolysis of urea in alkaline soils was studied under laboratory conditions. Soilsamples were collected from berseem (Trifolium alexandrinum), chickpea (Cicerarietinum), cotton (Gossypium hirsutum) and wheat (Triticum aestivum) fields.Urea was applied at 0.28, 0.56, 0.84, 1.12, 1.40 and 1.68 mg N g-1 soil. Ureatreated soil samples were incubated at 18 degree centigrade and, 32 degreecentigrade. A t the end o f the incubation period soil was extracted with 2 M KCIcontaining 5 mg phenyl mercuric acetate (PMA) L-1. Unhydrolyzed urea wasdetermined colorimetrically using Diacetyl monoxime method. The results showedthat substrate concentrations, temperature and cropping system had significanteffect on hydrolysis of urea in soil. At a concentration of 0.28 mg N g-1 soil ureawas completely hydrolyzed in soil from berseem and cotton fields in one day at32 degree centigrade; whereas in chickpea and wheat soil, only 63 and 52% ureawas hydrolyzed, respectively. Lowering the temperature of incubation retardedthe hydrolysis of urea; 42.24, 64.02, 58.28 and 29.12% urea was hydrolyzed in soilunder berseem, chickpea, cotton and wheat at 18 degree centigrade. Ureaconcentration greater than 0.28 mg N g-1 soil reduced hydrolysis of urea in soilunder berseem, chickpea, cotton and wheat both at 18 and 32 degree C. Theresults showed that urease activity was higher in soil under berseem and cottonas compared to that in chickpea and wheat soil.
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