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APPLYING SIMULATION TO IMPROVE RICE VARIETIES IN REDUCING THE ON-FARM YIELD GAP IN CAMBODIAN LOWLAND RICE ECOSYSTEMS
- P. L. POULTON, T. VESNA, N. P. DALGLIESH, V. SENG
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- Journal:
- Experimental Agriculture / Volume 51 / Issue 2 / April 2015
- Published online by Cambridge University Press:
- 10 September 2014, pp. 264-284
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Achieving export growth in rice production from variable rainfed lowland rice ecosystems is at risk if depending on conventional breeding or genetic development alone. Sustained, long-term production requires building adaption capacity of smallholder farmers to better manage the challenges of seasonal climate variability and future climate change. Better understanding of the risks and constraints that farmers face in managing their current cropping system helps develop strategies for improving rice production in Cambodia. System models are now considered valuable assessment tools for evaluating cropping systems performance worldwide but require validation at the local level. This paper presents an evaluation of the APSIM-Oryza model for 15 Cambodian rice varieties under recommended practice. Data from a field experiment in 2011, conducted in a non-limiting water and nutrient environment, are used to calibrate varietal-specific coefficients and model input parameters. An independent dataset is then used to validate the model performance for a ‘real-world’ situation using on-farm data for six rice varieties planted in 54 farmer fields on 32 farms in two villages of Southeastern Cambodia. From this analysis, the APSIM-Oryza model is shown to be an acceptable tool for exploring the mismatch between current on-farm yields and potential production through yield gap analysis and the exploration of cropping system options for smallholder farmers to increase production, adapt to seasonal climate variability and be prepared for potential climate changes.
Effects of irrigation, N fertilizer, cutting frequency and pesticides on ryegrass, ryegrass–clover mixtures, clover and lucerne grown on heavy and light land
- J. McEwen, W. Day, I. F. Henderson, A. E. Johnston, R. T. Plumb, P. R. Poulton, A. M. Spaull, D. P. Stribley, A. D. Todd, D. P. Yeoman
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- Journal:
- The Journal of Agricultural Science / Volume 112 / Issue 2 / April 1989
- Published online by Cambridge University Press:
- 27 March 2009, pp. 227-247
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The effects of irrigation, nitrogen fertilizer, cutting three or six times per year and a combined pesticide treatment that included aldicarb, phorate, benomyl and methiocarb on ryegrass (Lolium perenne) cv. S.23, either alone or in mixtures with white clover (Trifolium repens) cvs S.I00 or Blanca, and on lucerne (Medicago sativa) cv. Vertus grown on a silty clay–loam at Rothamsted and a sandy loam at Woburn were studied in 1977–81.
Benefits from irrigation were greater for six-cut than three-cut swards, with pesticides than without, for ryegrass with clover S. 100 than ryegrass with Blanca and at Woburnthan at Rothamsted. Lucerne did not benefit.
Responses of ryegrass to fertilizer N were best fitted by the model y = a + b/1+cx+dx2; and those of ryegrass–clover by the model y = a+bx (where y = yield, x = amount of N; a, b, c and d are constants). Without N, yields of ryegrass–Blanca clover mixtures considerably exceeded those of ryegrass–S.100. The former gave yields equivalent to those of ryegrass given 270 kg N/ha at Rothamsted and 330 kg N/ha at Woburn.
Lucerne without irrigation, N or pesticides gave yields in excess of all other unirrigated crops, even when these received pesticides and maximum N. Yields from three cuts of ryegrass greatly exceeded those from six cuts but yields of ryegrass–Blanca were greater from the six-cut regime.
Pesticides substantially improved the yields of ryegrass and clover, whether grown separately or mixed, but not those of lucerne. Pesticides not only controlled pests and diseases but also increased the incidence of vesicular–arbuscular mycorrhizas. The relative magnitude of yields of the different swards at the two sites differed, depending on treatment with irrigation, N fertilizer and pesticides. Differences between sites were removed or reversed by appropriate combinations of treatments.
Ryegrass–Blanca given no N fertilizer and cut six times removed 300 kg N/ha, an amount that was increased by irrigation and decreased by less frequent cutting; ryegrass–S.100 clover contained less N. Removals of P and K. often exceeded 35 and 300 kg/ha, respectively, each year. Herbage containing Blanca clover had much more Ca than that containing S.100 but at comparable yields all swards contained similar amounts of Mg.
Nitrogen deposition and its contribution to nitrogen cycling and associated soil processes
- K. W. T. GOULDING, N. J. BAILEY, N. J. BRADBURY, P. HARGREAVES, M. HOWE, D. V. MURPHY, P. R. POULTON, T. W. WILLISON
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- Journal:
- The New Phytologist / Volume 139 / Issue 1 / May 1998
- Published online by Cambridge University Press:
- 01 May 1998, pp. 49-58
- Print publication:
- May 1998
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Human activity has greatly perturbed the nitrogen cycle through increased fixation by legumes, by energy and fertilizer production, and by the mobilization of N from long-term storage pools. This extra reactive N is readily transported through the environment, and there is increasing evidence that it is changing ecosystems through eutrophication and acidification. Rothamsted Experimental Station, UK has been involved in research on N cycling in ecosystems since its inception in 1843. Measurements of precipitation composition at Rothamsted, made since 1853, show an increase of nitrate and ammonium N in precipitation from 1 and 3 kg N ha−1 yr−1, respectively, in 1855 to a maximum of 8 and 10 kg N ha−1 yr−1 in 1980, decreasing to 4 and 5 kg N ha−1 yr−1 today. Nitrogen inputs via dry deposition do, however, remain high. Recent measurements with diffusion tubes and filter packs show large concentrations of nitrogen dioxide of c. 20 μg m−3 in winter and c. 10 μg m−3 in summer; the difference is linked to the use of central heating, and with variations in wind direction and pollutant source. Concentrations of nitric acid and particulate N exhibit maxima of 1·5 and 2 μg m−3 in summer and winter, respectively. Concentrations of ammonia are small, barely rising above 1 μg m−3.
Taking deposition velocities from the literature gives a total deposition of all measured N species to winter cereals of 43·3 kg N ha−1 yr−1, 84% as oxidized species, 79% dry deposited. The fate of this N deposited to the very long-term Broadbalk Continuous Wheat Experiment at Rothamsted has been simulated using the SUNDIAL N-cycling model: at equilibrium, after 154 yr of the experiment and with N deposition increasing from c. 10 kg ha−1 yr−1 in 1843 to 45 kg ha−1 yr−1 today, c. 5% is leached, 12% is denitrified, 30% immobilized in the soil organic matter and 53% taken off in the crop. The ‘efficiency of use’ of the deposited N decreases, and losses and immobilization increase as the amount of fertilizer N increases. The deposited N itself, and the acidification that is associated with it (from the nitric acid, ammonia and ammonium), has reduced the number of plant species on the 140-yr-old Park Grass hay meadow. It has also reduced methane oxidation rates in soil by c. 15% under arable land and 30% under woodland, and has caused N saturation of local woodland ecosystems: nitrous oxide emission rates of up to 1·4 kg ha−1 yr−1 are equivalent to those from arable land receiving >200 kg N ha−1 yr−1, and in proportion to the excess N deposited; measurements of N cycling processes and pools using 15N pool dilution techniques show a large nitrate pool and enhanced rates of nitrification relative to immobilization. Ratios of gross nitrification[ratio ]gross immobilization might prove to be good indices of N saturation.
4 - Western Canada and United States
- Edited by Gerd E. G. Westermann, McMaster University, Ontario
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- The Jurassic of the Circum-Pacific
- Published online:
- 04 August 2010
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- 26 March 1993, pp 29-92
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Summary
INTRODUCTION
Prior to the general acceptance of the theory of plate tectonics, western North America was both a classic model and an enigma for structural geologists captivated by the eugeosyncline–miogeosyncline paradigm. Soon after the theory of plate tectonics settled in, accreted terranes followed, pioneered by one of the leaders of the plate-tectonic movement (Wilson 1968). Western North America, unique among the various boundary regions of the Pacific Ocean in being dominated by thin slivers of accreted terranes separated by transcurrent faults (Howell and Jones 1989), has played a leading role in the development of the concepts of terrane accretion. Insofar as the Jurassic was a primary period of accretion, the Jurassic rocks in western North American have played a major role in these developments.
The North American continent that split away from Europe during the Jurassic is estimated to have been 20–30% smaller than at present and to have grown by 300–500 km along its Pacific Coast by the accretion of about 100 terranes between 200 and 50 m.y. ago (Figure 4.1 A). The western margin of North America prior to about Middle Jurassic time was a passive margin (miogeocline), with mainly cratonic sediment sources, persisting 450 m.y. since a major Late Proterozoic rifting event (Sloss 1982; Stott and Aitken 1982).