Fertilizer nitrogen loss via N_2 emission from calcareous soil following basal urea application of winter wheat

The ratio of nitrous oxide(N2O)to N2O plus nitrogen gas(N2)emitted from soils(N2O/(N2O+N2))is regarded as a key parameter for estimating fertilizer nitrogen(N)loss via N2emission at local,regional or global scales.However,reliable measurement of soil N2emissions is still difficult in fertilized soil-crop systems.In this study,the N loss via N2emission following basal urea application(with a dose of 150 kg N ha-1)to a calcareous soil cultivated with winter wheat was quantified using the helium-based gas-flow-soil-core technique.Emissions of N2and N2O from sampled fresh soils were measured under simulated field soil temperature and oxygen conditions.Our observation performed on the first day after irrigation and rainfall events showed the highest N2and N2O emissions,which amounted to approximately 11.8 and 3.8μg N h-1kg-1dry soil,corresponding to 3304 and 1064μg N m-2h-1,respectively.The N2O/(N2O+N2)molar ratios within about 10 days following fertilization ranged from 0.07 to 0.25,which were much larger than those at the other time.During the one-month experimental period,the urea-N loss via emissions of N2,N2O,and N2+N2O was 1.6%,0.6%,and 2.2%,respectively.Our study confirms that the widely applied acetylene-inhibition method substantially underestimates fertilizer N losses via N2emissions from calcareous soils cultivated with winter wheat.

Reducing nitrogen runoff from paddy fields with arbuscular mycorrhizal fungi under different fertilizer regimes

Nitrogen（N） runoff from paddy fields serves as one of the main sources of water pollution. Our aim was to reduce N runoff from paddy fields by fertilizer management and inoculation with arbuscular mycorrhizal fungi（AMF）. In northeast China, Shuangcheng city in Heilongjiang province, a field experiment was conducted, using rice provided with 0%, 20%, 40%, 60%, 80%,and 100% of the local norm of fertilization（including N, phosphorus and potassium）, with or without inoculation with Glomus mosseae. The volume, concentrations of total N（TN）,dissolved N（DN） and particulate N（PN） of runoff water were measured. We found that the local norm of fertilization led to 18.9 kg/ha of N runoff during rice growing season, with DN accounting for 60%–70%. We also found that reduction in fertilization by 20% cut down TN runoff by 8.2% while AMF inoculation decreased N runoff at each fertilizer level and this effect was inhibited by high fertilization. The combination of inoculation with AMF and 80% of the local norm of fertilization was observed to reduce N runoff by 27.2%. Conclusively, we suggested that the contribution of AMF inoculation combined with decreasing fertilization should get more attention to slow down water eutrophication by reducing N runoff from paddy fields.