Nitrous oxide flux from wheat (National Agricultural Nitrous Oxide Research Program), Horsham, Victoria Australia, 2014. [Theme 5: Reducing emissions through improved nitrogen use efficiency]

Collection of gas samples for calculation of N2O emissions Samples were collected using static chambers of 250 mm placed on stainless steel bases that were inserted into the soil to a depth of 50 mm. The bases featured a channel which was filled with water prior to sampling to provide an air-tight seal around the base of the chamber. Chambers were removed from the plots between samplings. Chambers were located across crop rows and maintained free of all plants. Samples were collected on sampling days over a period of one hour between 9am and 1pm with three samples taken from each chamber. Prior to each sample being taken the assembly was 'flushed' by collecting and releasing three 25mL samples from within the chamber before a single 25mL sample was taken and placed in evacuated 'exetainer' (Labco ltd, High Wycombe, UK) 12 mL vials. Chambers were left open to the atmosphere between sampling days. Air temperature within the chamber and soil temperature was recorded at the time of sampling.

Gas samples analysed by Queensland University of Technology via gas chromtography. Soil and air temperature measured using Tiny Tag plus 2 temperature loggers.

Collection of crop production parameters Wheat grain yield was measured by cutting four 1m rows at ground level from each plot which were subsequently dried at 70Â°C before being hand thrashed. Both grain and straw were analysed for total N and grain protein determined by multiplying grain total N by 5.7 (Halvorson et al. 2004).

Grain and straw total N measured by LECO dry combustion

Collection of soil samples for site characterisation Prior to sowing, baseline deep soil samples were collected to a depth of 120cm in increments of 0-10cm, 10-20cm, 20-40cm, 40-80cm and 80-120cm. A total of three soil cores were randomly taken and bulked for each experimental block before being dried at 40Â°C, ground and sieved (<2.0mm) and analysed for soil mineral N (NO3- and NH4+). Additional analyses undertaken included: - pH (H20) 1:5 soil water extract measured using glass electrode - pH (CaCl2) 1:5 soil CaCl2 extract measured using glass electrode - EC 1:5 soil water extract measured using a probe - Total C Measured by combustion of air dried soils using LECO combustion analyser - Total N Measured by combustion of air dried soils using LECO combustion analyser - Organic carbon Measured using the Walkley and Black method - Lower storage limit (-1,500 kPa) determined using disturbed cores - Soil texture measured by laser - Soil bulk density was determined by soil corer >75mm inserted via hydraulic soil sampler to a depth of 60cm at 4 locations (NE, NW, SE & SW corners) within the trial. This was then divided into depts 0-10cm, 10-20cm, 20-30cm, 30-40cm, 40-50cm and 50-60cm. Extra 0-10cm cores were also taken by hand using 50mm bulk density rings.

Total C and total N measured by dry combustion using LECO analyser.

Trial design and site background The purpose of this trial was to investigate the impact of varying rates and timing of nitrogen fertiliser application as well as the potential for nitrification and urease inhibitors to mitigate nitrous oxide losses and improve productivity of a wheat crop. This trial was designed as a complete randomised block with 5 x replicates and 5 x core treatments monitored for N2O loss using static chambers with a further 5 treatments included that were not moniotred for N2O loss. For each plot being monitored for N2O emissions two static chambers were placed approximately 10cm apart, located across the crop rows. Treatments included: - Zero N* (control) - 12.5 kg N/ha of urea placed 25 mm below seed at sowing - 25 kg N/ha of urea placed 25 mm below seed at sowing - 50* kg N/ha of urea placed 25 mm below seed at sowing - 100 kg N/ha of urea placed 25 mm below seed at sowing - 25 kg N/ha of urea placed 25 mm below seed at sowing and 25 kg N/ha of urea top-dressed at GS30 - 25 kg N/ha of urea top-dressed at GS30 - 50* kg N/ha of urea top-dressed at GS30 - 25 kg N/ha of DMPP coated urea (Entec) placed 20 mm below seed at sowing - 50* kg N/ha of DMPP coated urea (Entec) placed 20 mm below seed at sowing - 25 kg N/ha as NBPT treated urea top-dressed at GS30 - 50* kg N/ha as NBPT treated urea top-dressed at GS30 *Treatments with static chambers installed. The 2014 experiment was conducted on a grey vertosol approximately 10kms west of Horsham on a Department of Economic Development, Jobs, Transport and Resources property with a long history of continuous cropping with a broad range of crops (cereals, pulses and canola), recent cropping history included barley in 2012 and Canola in 2013. The site was sown on the 20th of May to wheat (Triticum aestivum) cv. Scout (100 kg/ha) along with 128 kg/ha of single superphosphate banded with the seed. Chemical applications included a pre-sowing knockdown, pre-emergent and post emergent sprays for grasses and broadleaf weeds.

Collection of climatic data Daily weather data was collected onsite throughout the experimental period using an automatic logging weather station with rainfall analysed on a daily basis from 9am to 9am.

Data collected using an MEA (Magill, South Australia) weather station fitted with tipping bucket rain gauge, temperature and humidity sensors (fitted within a large radiation screen), wind speed and direction, evaporation, solar radiation and soil temperature sensors.