Ammonia loss from vegetable systems, Clyde, Victoria, 2014

NH3 measurement by open-path FTIR Open-path FTIR (one for each paddock) was established near the centre of each site such that the distance between the FTIR and the reflector mirror is ~70 m. Two reflector mirrors were used at the same location within each site, and established at two different heights (~0.5 m and ~ 1.6 m above crop canopy). A scanner attached to the FTIR enabled the beam to pass to the upper and lower mirror heights in sequence and hence enable calculation of the NH3 fluxes using a gradient flux technique. Measurements were conducted at 10-minute intervals for 1 week prior to and 3 weeks after manure application. Site 1, manure only, was considered as the background treatment and site 2 was to determine the impact of DMPP on NH3 loss.

Open-path FTIR

Soil mineral N Soil samples were collected at regular intervals from the vegetable bed (0-15, 15-30 cm layers) and from the corresponding furrow (0-15 cm layer) using a 2.5 cm id corer. Four replicate samples were collected by traversing each quadrat of the paddock from the corner to the centre. Fifteen samples were collected across each transect and composited, with a subsample then taken for analysis. Collected soil was dried at 40°C, sieved (<2mm) and extracted for mineral N with 2M KCl (1:5 ratio). The extract was filtered through a Whatman No. 42 filter paper and analysed for NH4+ and NO3- on the Skalar San++ segmented flow analyser.

Skalar San++ segmented flow analyser

N2O snapshots measurement Closed static chambers (50 x 50 cm x 25 cm high) were placed onto the beds. No measurements were done in the furrows as the measurements at Boneo showed there was minimal loss from this region. Four replicates were used at each site. On each sampling day, gas samples (20 mL) were collected at 0, 30 and 60 minutes after chamber closure using a gas-tight syringe, transferred into pre-evacuated Labco exetainers, transferred back to the University and analysed by gas chromatography.

Gas chromatograph

15N recovery Eight microplot treatments, each replicated 3 times, were established to measure the recovery of applied N in the plant and the soil by using 15NH415NO3, to plots with and without DMPP application.

Isotope ratio mass spectrometer

Biomass Biomass measurement was conducted to assess any productivity gain from DMPP application. At harvest, three plants from each of the 4 quadrats at each site were randomly selected and cut at ground level. The plants were dried at 60°C until constant weight.

Oven