Effect of Long-Term Application of Fertilizers and Manures on Nitrous Oxide Emissions from Soils Under Maize-Wheat Cropping System in Northern India.

Nitrous oxide (N₂O) emission from fertilized soils is a major contributor towards global green house gases emission from agriculture. Long-term experiments play an important role in understanding complex interactions among added inputs, plants, soil and climatic conditions and thus can be useful in understanding the effects of continuous application of fertilizers/manures and cropping on nitrous oxide emissions. A long-term fertilizer experiment under maize-wheat cropping system, in progress since 1972 at Punjab Agricultural University, Ludhiana, India, was selected to study nitrous oxide emissions from soils.  The treatments included application of nitrogenous fertilizers alone or in combination with phosphorous or potassium or farmyard manure (FYM) at different rates. N₂O fluxes from the soils were measured by closed chambers. N₂O fluxes varied significantly during the maize and wheat crop growing seasons and were related to fertilizer application and soil moisture. During maize cultivation, highest N₂O flux peaks were observed from 150% NPK treatments, while under FYM treatments peaks were the lower. Cumulative N₂O emissions during the maize crops were the vey high in 150%NPK and NPK100%+FYM treatments. During wheat season, N₂O fluxes varied from 11.5 to 19.7 N₂O-N g ha^-1day^-1 and were the highest in soils receiving 150% NPK fertilizers.