Soil net N and C mineralization and urea transformation in agroecosystems across North China Plain

To compare soil N supply capacity,urea transformation and nitrification in four regions of the North China Plain under intensive anthropogenic disturbance,we measured soil net N and C mineralization,nitrification and urea transformation in green house(GH) and field agroecosystems across elevation and fertilization gradients,namely,Luancheng(LF),Nanpi(NF) and Huimin(SF),by using 30d laboratory aerobic incubation.We found that net nitrification were positively correlated with net mineralization,indicating that the increase of NO3--N was the main result of net mineralization.The soil N supply capacity did not differ in North China Plain where the soils are highly disturbed and heavily fertilized with N.There were no significant differences in soil net mineralization and net nitrification either between manure and chemical fertilizer input,or among the regions in North China Plain.The soil net mineralization was 14.4,13.2,17.7 and 16.5 mg/kg during 30d incubation for GH,LF,NF and HF,respectively.However,Net C mineralization of GH,which was subjected to heavy manure application,was significantly lower than that in other three regions during incubation period.NO3--N was increased after urea hydrolysis,and about 63.4%～83.2% of ureaN was transformed to inorganic N in North China Plain,with the rate of urea transformation being significantly different among the four regions.1g of applied urea-N invoke a net nitrification increase of about NO3--N 0.69,0.82,0.64 and 0.63g/kg,and CO2 1.20,1.36,0.67 and 1.58 g/kg for GH,LF,NF and HF,respectively.