Impacts of organic and inorganic fertilizations on alfalfa yield, soil nitrate and greenhouse gas emissions.

Abstract

Field plot experiment was carried out during May 2012 to June 2014 to investigate the impacts of nitrogen fertilizations on the emissions of nitrous oxide (N2O) and methane (CH4) from alfalfa field as well as the dry matter yield and soil nitrate contents. Five treatments including CK, urea (100 kg N·hm-2, CF), urea (100 kg N·hm-2) + dairy cattle manure (60 kg N·hm-2) (DM1), urea (100 kg N·hm-2)+ digestate (60 kg N·hm-2) (DT) and reduced urea (40 kg N·hm-2)+ dairy cattle manure (60 kg N·hm-2) (DM2) were conducted. Results indicated that in comparison with CK, CF, DM1, DT and DM2 treatments significantly increased the dry matter yields of alfalfa by 44.2%, 38.9%, 56.3% and 30.6%, and increased the N2O emissions by 52.2%,89.1%, 133.7% and 59.4%, respectively, whereas the oxidation of atmospheric CH4 was reduced to different extents by these N management practices. The losses of N2O-N originated from urea and dairy cattle manure N accounted for 0.25%-0.28% of their inputs, whereas a greater va-lue of 0.64% was observed for digestate N. Applying urea or organic N to alfalfa field could significantly increase the dry matter yield without significant NO3--N leaching, however, it would lead to higher net CO2-equivalent emissions of producing 1 t dry matter of alfalfa.