C.F.E. Topp

Quantifying N2O emissions from intensive grassland production: the role of synthetic fertilizer type, application rate, timing and nitrification inhibitors

Increasing recognition of the extent to which nitrous oxide (N 2 O) contributes to climate change has resulted in greater demand to improve quantification of N 2 O emissions, identify emission sources and suggest mitigation options. Agriculture is by far the largest source and grasslands, occupying c . 0·22 of European agricultural land, are a major land-use within this sector. The application of mineral fertilizers to optimize pasture yields is a major source of N 2 O and with increasing pressure to increase agricultural productivity, options to quantify and reduce emissions whilst maintaining sufficient grassland for a given intensity of production are required. Identification of the source and extent of emissions will help to improve reporting in national inventories, with the most common approach using the IPCC emission factor (EF) default, where 0·01 of added nitrogen fertilizer is assumed to be emitted directly as N 2 O. The current experiment aimed to establish the suitability of applying this EF to fertilized Scottish grasslands and to identify variation in the EF depending on the application rate of ammonium nitrate (AN). Mitigation options to reduce N 2 O emissions were also investigated, including the use of urea fertilizer in place of AN, addition of a nitrification inhibitor dicyandiamide (DCD) and application of AN in smaller, more frequent doses. Nitrous oxide emissions were measured from a cut grassland in south-west Scotland from March 2011 to March 2012. Grass yield was also measured to establish the impact of mitigation options on grass production, along with soil and environmental variables to improve understanding of the controls on N 2 O emissions. A monotonic increase in annual cumulative N 2 O emissions was observed with increasing AN application rate. Emission factors ranging from 1·06–1·34% were measured for AN application rates between 80 and 320 kg N/ha, with a mean of 1·19%. A lack of any significant difference between these EFs indicates that use of a uniform EF is suitable over these application rates. The mean EF of 1·19% exceeds the IPCC default 1%, suggesting that use of the default value may underestimate emissions of AN-fertilizer-induced N 2 O loss from Scottish grasslands. The increase in emissions beyond an application rate of 320 kg N/ha produced an EF of 1·74%, significantly different to that from lower application rates and much greater than the 1% default. An EF of 0·89% for urea fertilizer and 0·59% for urea with DCD suggests that N 2 O quantification using the IPCC default EF will overestimate emissions for grasslands where these fertilizers are applied. Large rainfall shortly after fertilizer application appears to be the main trigger for N 2 O emissions, thus applicability of the 1% EF could vary and depend on the weather conditions at the time of fertilizer application.

Variation in grain skinning among spring barley varieties induced by a controlled environment misting screen

The current study investigated use of a controlled misting environment to simulate field conditions that have been implicated in high levels of the malting barley defect, grain skinning. More than 200 spring barley varieties were assessed to identify those varieties that were particularly resistant or susceptible to the defect. Relationships between skinning severity and the traits ear length, floret number, grain number and grain weight were examined among the varieties. In a panel of seven varieties chosen as treatment controls, misting was found to significantly increase skinning severity. The misting treatment had no effect on measured ear traits of these varieties. Among the 200 varieties grown under the misting treatment, there was a continuous spectrum of skinning severities, which were not correlated with ear length, floret number, grain number or grain weight. Using the misting treatment, differences in susceptibility to grain skinning could be determined among varieties. As the misting treatment did not affect measured ear traits, and no correlation was found between ear traits and skinning severity among varieties, the effect of misting on skinning severity must be mediated through other physiological characteristics.