Abstract:With the increasing of municipal sludge, applying sludge in agriculture has been of great concern. A field experiment was conducted to investigate the effects of applying urea, composted sludge and its combination with urea on the methane and nitrous oxide emissions from paddy soils and heavy metals accumulation in soil and plant. Five treatments, i. e. , no fertilization (CK), urea(U), urea and composted sludge(U+O)with a ratio of 7.5︰2.5(U7.5O2.5), 5︰5(U5O5), and total composted sludge(O)were installed, and the N application rate in treatments U, U+O, and O was the same(N, 240 kg/hm2). As the amount of sludge compost increased, the emission of CH4 increased linearly(P<0.05, r=0.967).Compared with treatment U, treatment O increased CH4 emission by 118%(P<0.05)and treatments U+O increased CH4 emission by 30%–34%(P>0.05). In contrast to the CH4, N2O emission reduced with the increasing composted sludge. Compared with treatment U, treatment O decreased N2O emission by 39%(P<0.05), treatment U+O decreased by 29%-38%(P<0.05). Treatments U and O had the same Greenhouse Gas Intensity(GHGI). Compared with treatment O, treatment U+O decreased GHGI by 18%-24%(P<0.05). The rice yield was no significant difference among the treatments. Compared with treatment U, treatment O increased Zn by 42%(P<0.05), Cr by 103%(P>0.05), Cu by 12%(P>0.05)in seed, treatment U+O increased Zn by 19%-27%(P<0.05), Cr by 14%-33%(P>0.05), Cu by 4%-7%(P>0.05)in seed, Ni was not detected in seed. Compared with treatment U, treatments U+O and O increased Cd by 33%(P>0.05). The heavy metal content in seed did not exceed the national standards. The combination of sludge compost and nitrogen fertilizer can be used as the recommended method for sludge compost in paddy field. But the soil heavy metal accumulation needs to be monitored.