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Conversion of long-term pasture to cropping was investigated for its effects on nitrous oxide ([N.sub.2]O) emissions in a 2-year field experiment in the high-rainfall zone of south-western Victoria. Early termination (pasture terminated 6 months before sowing) followed by winter (ETw) and spring (ETs) crops and late termination (pasture terminated 1 month before sowing) followed by a winter crop (LTw) were compared with continuous, mown pasture (MP). Emissions of [N.sub.2]O were measured with an automated gas sampling and analysing system. Emissions from MP were the lowest throughout the study, resulting in annual losses of 0.13 kg [N.sub.2]O-N [ha.sup.-1] in the first and the second years of the experiment. [N.sub.2]O-N loss was 0.6 kg [ha.sup.-1] from treatments without fallow in both years (LTw in 2013 and ETs in 2014). In the first year, annual losses from previous fallow in ETw and ETs plots were 7.1 and 3.6 kg [N.sub.2]O-N [ha.sup.-1], respectively. Higher annual [N.sub.2]O losses from treatments with fallow periods continued in the second year of the study and were 2.0 and 1.3 kg [N.sub.2]O-N [ha.sup.-1] from ETw and LTw treatments, respectively. High emissions were associated with N mineralisation and the accumulation of N[O.sub.3]-N in the soil during the extensive fallow period after early pasture termination or wheat harvest. Soil water content was a key factor influencing the temporal fluctuations in [N.sub.2]O emissions. Low emissions occurred when water-filled pore space was 65%, suggesting that denitrification was the major source of [N.sub.2]O emission. Crop grain yield was not affected by the duration of fallow (and therefore timing of pasture termination) in the first year, but was lower (P Additional keywords: fallow, nitrous oxide losses, pasture--crop system., Introduction Nitrous oxide ([N.sub.2]O) is a potent greenhouse gas, with an ozone-depleting potential ~300 times that of carbon dioxide (C[O.sub.2]) and 12 times that of methane (C[H.sub.4]) (Crutzen and Ehhalt [...]

The effects of elevated concentrations of atmospheric CO2 (e[CO2]) on the nutritive value of wheat vegetative matter and grain as a feedstock for ruminants were investigated in a study undertaken at the Australian grains free‐air CO2 enrichment (AGFACE) facility. The study included two commercial wheat cultivars (Janz and Yitpi) and two genetic selections from a Seri/Babex population (SB003 and SB062) which had previously been characterised for low and high water‐soluble carbohydrate accumulation efficiency. The trial was grown under ambient (~390 µmol/mol) and elevated (~550 µmol/mol) CO2 conditions, and plants harvested at tillering, anthesis and physiological maturity. Composition analyses to determine the nutritive value for ruminant feed were undertaken on stems, leaves and grain. Plant and grain nitrogen were reduced in the e[CO2] treatments, and as expected, the water‐soluble carbohydrates increased. All genotypes responded to e[CO2] with the effects of altered composition evident within 60 days of sowing. Determinants of ruminant feed quality such as neutral and acid detergent fibre and estimated in vitro metabolisable energy were not significantly affected. The reduced plant and grain N will impact on the nutritive value and supplementation may be required. The impact of e[CO2] on chemical composition of wheat plants may be greater if the predicted climate change is associated with concomitant abiotic stress such as high ambient temperature or low soil moisture. [ABSTRACT FROM AUTHOR]

Nitrogen (N) management is critical to the profitability of grain production systems, however careful management of fertiliser is needed to minimise environmental impacts. We investigated the effect of five N fertilisation strategies on nitrous oxide (N2O) emissions and nitrogen use efficiency (NUE) of rainfed wheat grown on a clay soil in a temperate, semi-arid environment of south eastern Australia during 2013 and 2014. Treatments included urea application (50 kg N/ha) at sowing with and without nitrification inhibitor (3,4-dimethylpyrazole phosphate) and surface broadcasting of urea with and without urease inhibitor (n-butyl thiophosphoric triamide) at the end of tillering plus an unfertilised control. Daily N2O emissions were low and responsive to in-season rainfall and fertiliser addition at sowing. Cumulative emissions from sowing until harvest were highest where N was applied at sowing in 2013; 160 g N2O-N/ha, while the 0 N control emitted 28 g N2O-N/ha (over 201 days). Emissions during 2014 were 77% lower than 2013 due to dry seasonal conditions; cumulative emissions were 49 g N2O-N/ha where N was applied at sowing, with background emissions of around 0 g N2O-N/ha (over 177 days). Inhibitors showed limited scope for reducing N2O emissions in this environment, however deferring N application until the end of tillering reduced N2O emissions. Grain yield responses to fertiliser were significant; increasing grain yield by 11-31% and NUE was generally high (recovery efficiency > 68%). However, deferring N application until the end of tillering in 2014 reduced yield (− 19%) and recovery of applied N (− 74%). [ABSTRACT FROM AUTHOR]

Wheat production will be impacted by increasing concentration of atmospheric CO2 [ CO2], which is expected to rise from about 400 μmol mol−1 in 2015 to 550 μmol mol−1 by 2050. Changes to plant physiology and crop responses from elevated [ CO2] (e[ CO2]) are well documented for some environments, but field-level responses in dryland Mediterranean environments with terminal drought and heat waves are scarce. The Australian Grains Free Air CO2 Enrichment facility was established to compare wheat ( Triticum aestivum) growth and yield under ambient (~370 μmol−1 in 2007) and e[ CO2] (550 μmol−1) in semi-arid environments. Experiments were undertaken at two dryland sites (Horsham and Walpeup) across three years with two cultivars, two sowing times and two irrigation treatments. Mean yield stimulation due to e[ CO2] was 24% at Horsham and 53% at Walpeup, with some treatment responses greater than 70%, depending on environment. Under supplemental irrigation, e[ CO2] stimulated yields at Horsham by 37% compared to 13% under rainfed conditions, showing that water limited growth and yield response to e[ CO2]. Heat wave effects were ameliorated under e[ CO2] as shown by reductions of 31% and 54% in screenings and 10% and 12% larger kernels (Horsham and Walpeup). Greatest yield stimulations occurred in the e[ CO2] late sowing and heat stressed treatments, when supplied with more water. There were no clear differences in cultivar response due to e[ CO2]. Multiple regression showed that yield response to e[ CO2] depended on temperatures and water availability before and after anthesis. Thus, timing of temperature and water and the crop's ability to translocate carbohydrates to the grain postanthesis were all important in determining the e[ CO2] response. The large responses to e[ CO2] under dryland conditions have not been previously reported and underscore the need for field level research to provide mechanistic understanding for adapting crops to a changing climate. [ABSTRACT FROM AUTHOR]