Nitrous oxide and nitric oxide fluxes from cornfield, grassland, pasture and forest in a watershed in Southern Hokkaido, Japan(Environment)

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To develop an advanced method for estimating nitrous oxide (N_2O) emission from an agricultural watershed, we used a closed-chamber technique to measure seasonal N_2O and nitric oxide (NO) fluxes in cornfields, grassland, pastures and forests at the Shizunai Experimental Livestock Farm (467ha) in southern Hokkaido, Japan. From 2000 to 2004, N_2O and NO fluxes ranged from -137 to 8,920μgNm^<-2> h^<-1> and from -12.1 to 185μgNm^<-2> h^<-1>, respectively. Most N_2O/NO ratios calculated on the basis of these N_2O and NO fluxes ranged between 1 and 100, and the log-normal N_2O/NO ratio was positively correlated with the log-normal N_2O fluxes (γ^2=0.346,P<0.01). These high N_2O fluxes, therefore, resulted from increased denitrification activity. Annual N_2O emission rates ranged from -1.0 to 81kgNha^<-1> year^<-1> (average =6.6kgNha^<-1>). As these emission values varied greatly and included extremely high values, we divided them into two groups: normal values (i.e. values lower than the overall average) and high values (i.e. values higher than average). The normal data were significantly positively correlated with N input (γ^2=0.61,P<0.01) and the "higher" data from ungrazed fields were significantly positively correlated with N surplus (γ^2=0.96,P<0.05). The calculated probability that a high N_2O flux would occur was weakly and positively correlated with precipitation from May to August. This probability can be used to represent annual variation in N_2O emission rates and to reduce the uncertainty in N_2O estimation.

Nitrous oxide and nitric oxide fluxes from cornfield, grassland, pasture and forest in a watershed in Southern Hokkaido, Japan(Environment)

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