Nitrous oxide emissions from cattle-impacted pasture soil amended with nitrate and glucose

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There is little information concerning N2O fluxes in the pasture soil that has received large amounts of nutrients, such as urine and dung, for several years. The aims of this study were to (1) experimentally quantify the relationship between mineral N input and N2O emissions from denitrification, (2) describe the time course of N2O fluxes resulting in N inputs, and (3) find whether there exists an upper limit of the amount of nitrogen escaping the soil in the form of N2O. The study site was a grassland used as a cattle overwintering area. It was amended with KNO3 and glucose corresponding to 10–1,500 kg N and C per hectare, covering the range of nutrient inputs occurring in real field conditions. Using manual permanent chambers, N2O fluxes from the soil were monitored for several days after the amendments. The peak N2O emissions were up to 94 mg N2O–N m−2 h−1, 5–8 h after amendment. No upper limit of N2O emissions was detected as the emissions were directly related to the dose of nutrients in the whole range of amendments used, but the fluxes reflected the soil and environmental conditions, too. Thus, in three different experiments performed during the season, the total cumulative losses of N2O–N ranged from 0.2 to 5.6% of the applied 500kg \(\operatorname{N} \operatorname{O} _{3} ^{ - } - \operatorname{N} \) ha−1. Splitting of high nutrient doses lowered the rate of N2O fluxes after the first amendment, but the effect of splitting on the total amount of N2O–N released from the soil was insignificant, as the initial lower values of emissions in the split variants were compensated for by a longer duration of gas fluxes. The results suggest that the cattle-impacted soil has the potential to metabolize large inputs of mineral nitrogen over short periods (∼days). Also, the emission factors for \( \operatorname{N} \operatorname{O} _{3} ^{ - } \, - \operatorname{N} \) did not exceed values reported in literature.