Summary. Two lines of perennial ryegrass (Lolium perenne L.), cv. Aurora and breeding line Ba 11351, from the United Kingdom with elevated concentrations of water-soluble carbohydrates in the shoot were compared with the standard cultivars, Ellett, Vedette and Kangaroo Valley, in pure grass swards under irrigation at Kyabram, Victoria, and Gatton, Queensland, and under natural rainfall at Condah, Victoria, during 1995–97. Near infrared reflectance spectroscopy was used to predict the water-soluble carbohydrate, crude protein, in vitro dry matter digestibility, neutral and acid detergent fibre, and Klason lignin concentrations of the perennial ryegrass herbage. Herbage yield and water-soluble carbohydrate differed between cultivars at each site at most harvests, with the high water-soluble carbohydrate lines usually yielding less and having higher water-soluble carbohydrate concentrations than the 3 standard cultivars. However, the high water-soluble carbohydrate lines also had higher water-soluble carbohydrate concentrations at harvests where their yield was equal to the standard cultivars. The other nutritive value traits differed significantly at more than half of the 32 harvests: the high water-soluble carbohydrate lines had higher crude protein and dry matter digestibility, and lower neutral detergent fibre, the neutral detergent fibre containing less acid detergent fibre and lignin than did the standard cultivars. The high water-soluble carbohydrate lines were more susceptible to crown rust during spring and summer than the standard cultivars at Kyabram and Gatton: heavy infections reduced yield, water-soluble carbohydrate, dry matter digestibility and crude protein. Higher water-soluble carbohydrate may depend on only a few genes, as does rust resistance and it seems likely that high yielding, high water-soluble carbohydrate cultivars can be developed by recombination and selection.

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Understanding spatial variability of emissions of nitrous oxide (N 2 O) is essential to understanding of N 2 O emissions from soils to the atmosphere and in the design of statistically valid measurement programs to determine plot, farm and regional emission rates. Two afternoon, 'snap-shot' experiments were conducted; one in the summer and one in the autumn of 2004, to examine the statistics and soil variables affecting the spatial variability of N 2 O emissions at paddock scale. Small, static chambers (mini-chambers) were placed at 100 locations over an 8,100 m 2 area of irrigated dairy pasture in northern Victoria, Australia. Chamber headspace was sampled for N 2 O and soil samples taken below each mini-chamber were analysed for soil nitrate (NO 3 -), ammonium (NH 4 + ) and other chemical and physical properties known to affect N 2 O emissions. The experiments took place immediately after the sequence of grazing, urea application and irrigation. Nitrous oxide emissions and soil variables were analysed using classical statistics to investigate the effect of soil variables on N 2 O emissions. Geostatistics were used to investigate spatial patterns of N 2 O emissions and soil variables over the measurement area. Nitrous oxide emissions were extremely variable; 45-765 ng N 2 O-N m −2 s −1 and 20-953 ng N 2 O-N m −2 s −1 for the two experiments with corresponding averages of 165 and 138 ng N 2 O-N m −2 s −1 . Nitrous oxide emissions showed spatial dependence up to 73 and 51 m for the two experiments. Nitrous oxide emissions showed significant correlation with soil nutrients in decreasing order of NO 3 -, NH 4 + and available-P concentrations. There was no significant correlation of N 2 O emissions with measured soil physical properties.

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The nitrification inhibitor, 3,4-dimethylpyrazol-phosphate (DMPP) and the urease inhibitor N-(n-butyl) thiophosphoric triamide (nBTPT) can mitigate N losses through reducing nitrification and ammonia volatilization, respectively. However, the impact of repeated applications of these inhibitors on nitrogen cycling microorganisms is not well documented. This study aimed to investigate the changes in the abundance and community structure of the functional microorganisms involved in nitrification and denitrification in Australian pasture soils after repeated applications of DMPP and nBTPT.Materials and methods Soil was collected in autumn and spring, 2014 from two pasture sites where control, urea, urea ammonium nitrate, and urea coated inhibitors had been repeatedly applied over two years. Soil samples were analyzed to determine the potential nitrification rates (PNRs), the abundances of amoA, narG, nirK and bacterial 16S rRNA genes, and the community structure of ammonia oxidizers.Results and discussion Two years of urea application resulted in a significantly lower soil pH at Terang and a significant decrease in total bacterial 16S rRNA gene abundance at Glenormiston, and led to significantly higher PNRs and abundances of ammonia oxidizers compared to the control. Amendment with either DMPP or nBTPT significantly decreased PNRs and the abundance of amoA and narG genes. However, there was no fertilizer-or inhibitor-induced change in the community structure of ammonia oxidizers.Conclusions These results suggest that there were inhibitory effects of DMPP and nBTPT on the functional groups mediating nitrification and denitrification, while no significant impact on the community structure of ammonia oxidizers was observed. The application of nitrification or urease inhibitor appears to be an effective approach targeting specific microbial groups with minimal effects on soil pH and the total bacterial abundance. Keywords 3,4-dimethylpyrazole phosphate (DMPP) • Ammonia-oxidizing archaea • Ammonia-oxidizing bacteria • N-(n-butyl) thiophosphoric triamide (nBTPT)