A large proportion of soil nitrogen is found in organic forms. Urease plays an essential role in the mineralization of organic nitrogen as well as urea. Agronomic and vegtable crops can affect urease activity in rhizosphere. The aim of our study was to determine the effects of some agronomic and vegtable crops on urease activity and total N in their rhizosphere. The agronomic and vegtable crops were planted in a semiarid soil in the pots under greenhouse condition. Urease activity, total N, total organic carbon and C/N ratio in the rhizosphere of any species was studied at middle and end vegetative growth of plants. Total N decreased significantly in the rhizosphere of all species. It was higher in the control soil (1.1 mg kg-1) and decreased from 0.9 mg kg-1 in rhizosphere of Cicer arietinum to 0.4 mg kg-1 in rhizosphere of Allium cepa. Urease activity was greatly enhanced in the rhizosphere of all species. It increased 7.2-343.5% in the middle of vegetative growth and 140.2- 473.9% in the end of vegetative growth in the rhizosphere compared to non-rhizosphere soil. Urease activity increased in rhizospheric soil of the plants at the end of vegetative growth. However only in rhizosphere of A.cepa this increase was statistically significant. It may be related to lower total N and higher C/N ratio in rhizosphere of A.cepa.
