[Effects of Biochar Amendment and Irrigation on Denitrification Losses in Greenhouse Tomato Fields]

Biochar addition and irrigation are normal farm practices for tomatoes management, while their impacts on denitrification are less known. In this study, three irrigation treatments(hereafter main plots)were set as 50% (W50%), 75% (W75%) and 100% (W100%) of reference evapotranspiration (ET₀), and the subplots coupled three biochar treatments at the rates of 0 (B0), 25 t·hm^-2 (B25) and 50 t·hm^-2 (B50). Typical soil samples in each plot were collected when tomatoes were harvested in 2014 and 2015. We used acetylene inhibition method to study the denitrification loss, and also measured N₂O emissions of tomato soil without acetylene amendment. The results showed that biochar and irrigation significantly changed the physical and chemical properties of the soil. Adding biochar improved total carbon, total nitrogen content and pH of the soil, while reduced the content of NH₄⁺-N and NO₃^--N compared to B0. On the contrary, irrigation reduced the amount of total nitrogen and total carbon content. As a result, both biochar and irrigation significantly reduced denitrification losses (P<0.05). Moreover, the interaction of biochar and irrigation significantly reduced soil inorganic nitrogen and denitrification losses (P<0.05),and the orders of the influencing factors of NO₃^--N were irrigation, biochar, their interactions in turn, the orders of the influencing factors of NH₄⁺-N were biochar, irrigation, their interactions in turn, the orders of the influencing factors of denitrification losses were irrigation, biochar, their interactions in turn. Denitrification losses were positively related to inorganic nitrogen content in the soil, CO₂mineralization rates and N₂O emission rates. The ratio of N₂O/D_N, ranging from 0.31% to 1.88%, was significantly affected by biochar and irrigation treatment in the fields (P<0.05).