Ammonia loss from temperate pasture systems. Wye, South Australia, 2014 Autumn

NH3 measurements by passive samplers The Leuning ammonia samplers were placed at one height (0.8 m, ZINST) at the centre of each treatment circle (50 m diameter). Two masts with the same height as the treatment circles were established for background measurements. Background measurements were made upwind and downwind of the treated circles, at least 50 m from the edge of the closest circle. Samplers were changed twice per day (0800-1700 and 1700-0800 hrs) for a week after fertiliser application, then daily for another week and every 2-3 days for the third and final week. Trapped ammonia was eluted from the NH3 samplers on site using MilliQ water. Eluted samples were placed in the freezer and then transported under refrigeration back to the University of Melbourne and analysed with the Skalar San++ segmented flow analyser.

The Leuning et al. (1985) passive samplers

N2O snapshots measurement N2O fluxes were measured by closed static chambers (50 x 50 m square, 25 cm height) for the three treatments plus background with four replications/treatment. The chambers were placed at a separate location in the background area within the pasture site. This was to avoid interference of air movement and disturbance to the circular treatment area caused by the N2O work. N2O gas samples were collected daily for the first week, and then every second day for second and third weeks after the treatments were applied. On each sampling day, gas samples (20 mL) were collected at 0, 45 and 90 minutes after chamber closure using a gas-tight syringe, transferred into pre-evacuated exetainers, transferred back to the University of Melbourne and analysed by gas chromatography.

Gas chromatograph

Soil mineral N Soil samples (0-10 cm) were collected daily for three days after fertiliser application, then every second day for the following two weeks using a 2.5 cm id corer. Ten soil cores were collected per quarter of the treatment circles, following the same transect from one edge to the middle at each sample time. Each set of 10 samples was composited, with a subsample then taken for analysis. Additional background soil was collected from the areas between the treatment circles and composited. Collected soil was kept frozen at –18°C and will be extracted with 2M KCl-PMA. The extract will be filtered through a Whatman No. 42 filter paper and analysed for urea, NH4+ and NO3- on the Skalar San++ segmented flow analyser.

San++ segmented flow analyser

Biomass Pasture biomass cuts were taken from four replicates from the small plot trial associated with this experiment at the completion of the NH3 measurements. Collected samples were dried at 60°C for 72 hrs and weighed.

Oven

15N recovery Microplots (55 cm length by 45 cm width) were established on the background areas of the site with three replications. 15N-enriched granular urea (~10% atom excess) was applied to the microplots at a rate of 50 kg N/ha. Inhibitor treatments were applied to the 15N granular urea and immediately placed into the microplots. The treatments were; 1) 15N granular urea + water 2) 15N granular urea + NBPT @ 2 L/tonne as Lockdown (to make Green UreaNV equivalent) 3) 15N granular urea + DMPP @ 3.5 L/tonne (to make Urea with ENTEC equivalent) At the end of the experiment (May 26th), the entire core was removed from site and divided into 0-5 cm, 5-10 cm and 10-15 cm sections. Additional soil was collected from beneath the plots, with 3 composite cores (2.5 cm i.d) taken from 15-25 cm and 25-35 cm. Plant (above and below-ground (0-5 cm layer)) samples were collected (together with reference soil and plant samples). All samples are being processed and will be analysed for total N and 15N enrichment by isotope ratio mass spectrometry. Samples collected were dried at 40°C and 60°C for soil and plant samples, respectively, until constant weight. Plant samples will be ground using a tissue-lyser. Total sample weights were recorded to enable calculation of recovery. Soil samples will be crushed into 2 mm pieces, homogenized, and subsampled for fine grinding using a pulveriser. Another subsample will be dried at 105°C for moisture content.