Spatial pattern of soil properties in an irrigated field

Non-Peer ReviewedDenitrification from agricultural ecosystems is regarded as a major contributor to atmospheric N levels, but the actual rates of denitrification and the controls on these rates remain poorly understood. This study was conducted to examine landscape-scale patterns of denitrification and the soil properties that control these patterns. Two sampling grids (11 x 11 m and 110 x 110 m) were established in an irrigated field in an aridic Boroll (Brown Chernozemic) soil in southern Saskatchewan. The measured soil properties (denitrification rate, respiration rate, volumetric moisture content, bulk density, soluble organic and inorganic carbon, total and mineral N, in situ pH, and in situ redox potential) were correlated to slope properties and derived landform elements at the site to determine landscape-scale patterns and relationships. The soil properties occurred in one of three spatial patterns: (i) a random pattern for mineral N; (ii) a diagonal pattern for pH, soluble organic and inorganic carbon, and total N; and (iii) a depression-centered pattern for denitrification, bulk density, moisture, respiration and redox potential. Statistically distinct rates of denitrification were associated with the different landform elements: rates were lowest in the shoulder elements, intermediate in the footslope and level-convex elements, and highest in the level-concave elements. Hot-spots of denitrification activity, i.e., sampling sites with denitrification rates statistically identified as outliers, were all associated with the level elements and, predominantly, the level-concave elements

Temporal denitrification at the landscape scale in a Black soil

Non-Peer ReviewedLandscape scale and seasonal pattern of denitrification activity have to be incorporated in a model to estimate total N losses. A study was conducted to exam the seasonal variability of denitrification in a landscape near Blaine Lake, Saskatchewan. A 120 x 120 m sampling grid, separated by a spacing of 10 m, was established in a Black Chernozem soil. The area was surveyed, landform elements identified and from each landform element ten sampling points were further selected and sampled throughout the season for denitrification activity by the acetylene-blockage approach. Soils samples were taken seven times during the entire 1991 season before the area was prepared for seeding in the spring, following precipitation events during the growing season , and in the fall at the onset of frost. Following incubation, soil samples were analyzed for percent moisture, NH4+ and NO3-, soluble organic carbons, and total soil respiration. The distribution of denitrification activities were highly skewed and followed a distinct landscape pattern that remained consistent throughout the year. Denitrification activity increased significantly after the occurrence of a precipitation event and was further enhanced after the application of fertilizer-N, ceased toward the end of the growing season and became zero at the fall sampling. Moisture was the most dominant parameter controlling denitrification activity followed by the concentration of and NH4+ and NO3-. The highest denitrification activity occurred on the divergent and convergent footslopes, the lowest activity on the divergent shoulder and upper level landform elements, a landscape scale pattern that remained consistent throughout the year, independent of the magnitude of activity. Ambient evolution of N2O and denitrification activity followed predominantly a similar temporal and landscape scale pattern. By estimating the duration of a denitrification following a precipitation event at the various landform elements and correcting for the percentage each landform element occupies in the landscape, the total denitrification per precipitation during the early part of the season was estimated at 357 g N ha-1 cycle-1. In conclusion, results indicates that landscape scale pattern of denitrification remained constant throughout the growing season and was predominantly induced by precipitation events

The use of large undisturbed cores to assess soil quality-yield relationships in the greenhouse

Non-Peer ReviewedLarge undisturbed cores were taken from different landscape positions (divergent shoulders, DSH, and convergent footslopes, CFS) at two sites in the Black soil zone. The soils are classified as belonging to the Oxbow association and have been cultivated for 15 and 82 years. The cores were used in a greenhouse experiment to study the effect of soil quality on yield of spring wheat (var. Katepwa) at three levels of simulated growing season precipitation: low (123 mm season-1), mid (189 mm season-1), and high (332 mm season-1). Grain yields in the DSH cores increased with increasing precipitation for both the 15- and 82-year soils. Moreover, the 15-year DSH cores out-yielded their 82-year counterparts by 50, 76, and 85% at the low, mid, and high water levels, respectively. Cores from the CFS positions were watered only at the mid-water level. Grain yields in the 15- and 82-year CFS cores and the 15-year DSH cores were not significantly different (P < 0.05). The results of this study indicate that soil quality is a relatively minor factor when water is limiting but assumes a much greater role in years of normal or above normal growing season precipitation. These initial results also suggest that large cores are a feasible and cost-effective means of studying soil-plant relationships in the greenhouse or growth chamber

Microbial enzyme activity in irrigated canola plots receiving different nitrogen applications

Non-Peer Reviewe

Spatial variability of deep leached nitrate as related to denitrification in a prairie landscape

Non-Peer ReviewedDenitrification is an anaerobic process that converts NO3- to N2 and N2O, and is considered one of the most highly variable soil processes within a landscape. Moisture acting in response to hillslope hydrological processes controls rates of denitrification and leaching at the landform level. In 1991, a field study was conducted in the Black Soil Zone of an undulating landscape (3-5% slope) at Blaine Lake, Saskatchewan to determine the amount of nitrate leached below the rooting zone and its possible relationship to denitrification. Nitrate has been leached and translocated in the upper regolith in response to water movement where significant leaching of soluble components occurred in depressional areas to depths beyond 3 m. The amount of nitrate at depth was greatest in shoulder and upper level elements where it reached a maximum of 95 ug g-1 at the 1.5 m depth. Footslope and lower level elements contained the lowest nitrate levels (<1 ug g-1) within the 3m sampled area. High rates of denitrification occurred in footslope and lower level elements, compared to significantly lower rates on divergent shoulder and upper level elements. Nitrate content at depth was inversely correlated with denitrification activity (-0.485 ***). High mean concentrations of nitrate were therefore, spatially related to low rates of denitrification activity in response to hydrological spatial variation

ILRI in Asia: an assessment of priorities for Asian livestock research and development

The purpose of this discussion paper is, firstly, to promote debate amongst potential clients of ILRI's research in South and South-East Asia on what ILRI could do in these regions, in collaboration with the NARS, which will assist the development of the livestock industries and, secondly, to provide advice to the ILRI Board and management on the rational for ILRI involvement in the regions, the nature of that involvement, and the mechanisms and process by which ILRI might maximise the benefits from its investment into research and development, particularly in these regions. The paper looks initially at the economic trends in selected countries in both regions and assesses the likely impact of this on dietary preferences and priorities. Having established the potential demands in the regions for the major livestock products (meat, milk, draft-power, eggs and, to a lesser extent, leather, wool and hair) in the next decade or so, the ways in which deficits in supply can be met from existing systems are assessed. The major constraints to improved production are identified and the role that technologically based research can play in alleviating these constraints is examined. The discussion paper then canvasses options for ILRI's participation, facilitation and leadership in some areas of priority research for the region and some possible mechanisms by which ILRI might achieve such objectives are detailed

Ultramafic xenoliths from the Bearpaw Mountains, Montana, USA: evidence for multiple metasomatic events in the lithospheric mantle beneath the Wyoming craton

Ultramafic xenoliths in Eocene minettes of the Bearpaw Mountains volcanic field (Montana, USA), derived from the lower lithosphere of the Wyoming craton, can be divided based on textural criteria into tectonite and cumulate groups. The tectonites consist of strongly depleted spinel lherzolites, harzburgites and dunites. Although their mineralogical compositions are generally similar to those of spinel peridotites in off-craton settings, some contain pyroxenes and spinels that have unusually low Al2O3 contents more akin to those found in cratonic spinel peridotites. Furthermore, the tectonite peridotites have whole-rock major element compositions that tend to be significantly more depleted than non-cratonic mantle spinel peridotites (high MgO, low CaO, Al2O3 and TiO2) and resemble those of cratonic mantle. These compositions could have been generated by up to 30% partial melting of an undepleted mantle source. Petrographic evidence suggests that the mantle beneath the Wyoming craton was re-enriched in three ways: (1) by silicate melts that formed mica websterite and clinopyroxenite veins; (2) by growth of phlogopite from K-rich hydrous fluids; (3) by interaction with aqueous fluids to form orthopyroxene porphyroblasts and orthopyroxenite veins. In contrast to their depleted major element compositions, the tectonite peridotites are mostly light rare earth element (LREE)-enriched and show enrichment in fluid-mobile elements such as Cs, Rb, U and Pb on mantle-normalized diagrams. Lack of enrichment in high field strength elements (HFSE; e.g. Nb, Ta, Zr and Hf) suggests that the tectonite peridotites have been metasomatized by a subduction-related fluid. Clinopyroxenes from the tectonite peridotites have distinct U-shaped REE patterns with strong LREE enrichment. They have 143Nd/144Nd values that range from 0·5121 (close to the host minette values) to 0·5107, similar to those of xenoliths from the nearby Highwood Mountains. Foliated mica websterites also have low 143Nd/144Nd values (0·5113) and extremely high 87Sr/86Sr ratios in their constituent phlogopite, indicating an ancient (probably mid-Proterozoic) enrichment. This enriched mantle lithosphere later contributed to the formation of the high-K Eocene host magmas. The cumulate group ranges from clinopyroxene-rich mica peridotites (including abundant mica wehrlites) to mica clinopyroxenites. Most contain >30% phlogopite. Their mineral compositions are similar to those of phenocrysts in the host minettes. Their whole-rock compositions are generally poorer in MgO but richer in incompatible trace elements than those of the tectonite peridotites. Whole-rock trace element patterns are enriched in large ion lithophile elements (LILE; Rb, Cs, U and Pb) and depleted in HFSE (Nb, Ta Zr and Hf) as in the host minettes, and their Sr–Nd isotopic compositions are also identical to those of the minettes. Their clinopyroxenes are LREE-enriched and formed in equilibrium with a LREE-enriched melt closely resembling the minettes. The cumulates therefore represent a much younger magmatic event, related to crystallization at mantle depths of minette magmas in Eocene times, that caused further metasomatic enrichment of the lithosphere

Contribution of ephemeral wetlands to annual nitrous oxide flux from an agricultural landscape

Non-Peer ReviewedMeasurement of soil nitrous oxide emissions from soil in the Canadian Prairie Region rarely includes uncultivated ephemeral wetlands (UW) within agricultural landscapes. Accurate inventories and a better understanding spatial and temporal variability for soil N2O in agricultural terrains requires flux measurements from non-agricultural areas of the field. The purpose of this study was to measure soil nitrous oxide flux from an agricultural landscape that includes UW. Measurements were taken weekly and bi-weekly from July to October of 2003 and from March to October of 2004 and 2005. Cumulative emissions were highest from concave elements (cultivated ephemeral wetlands) (CV) elements in 2003 and 2004 and highest from the basin centers (BC) of UW in 2005. High flux events were associated with rainfall in 2003, and the recession of standing water at CV and BC elements in 2004 and 2005. However, there are differences between ephemeral wetlands in their emission response to water recession. Accounting for aerial extent of landscape units reveals that CV elements make greatest contribution to total yearly flux. Beneficial management practices intended to reduce annual emissions from this site should be designed to reduce emission from CV elements and UW should not be cleared for crop production. Sampling designs for measurement of emissions from UW need not distinguish between riparian grass and riparian tree elements within the UW

High-power master-oscillator power amplifiers based on rare-earth-doped fibres

In recent years there have been dramatic advances in fibre lasers. Currently, conventional single-strand cladding-pumped fibre lasers can generate output powers beyond 1 kW with high beam quality. Indeed, this fibre circuitry combined with pump-diode technology provides a unique high-gain environment for robust designs, which is also all-solid state, compact, stable, reliable, and reproducible. Here we review the recent progress in high-power MOPAs based on rare-earth-doped fibres and discuss fundamental aspects and prospects. We present our up-to-date experimental results with particular attention to a multitude of cladding-pumped, refined power amplifier regimes, including continuous-wave and pulsed fibre MOPA sources based on ytterbium-doped fibres operating at 1.1 µm and erbium:ytterbium co-doped fibres at 1.5 µm

Weak Localization Effect in Superconductors by Radiation Damage

Large reductions of the superconducting transition temperature $T_{c}$ and the accompanying loss of the thermal electrical resistivity (electron-phonon interaction) due to radiation damage have been observed for several A15 compounds, Chevrel phase and Ternary superconductors, and $\rm{NbSe_{2}}$ in the high fluence regime. We examine these behaviors based on the recent theory of weak localization effect in superconductors. We find a good fitting to the experimental data. In particular, weak localization correction to the phonon-mediated interaction is derived from the density correlation function. It is shown that weak localization has a strong influence on both the phonon-mediated interaction and the electron-phonon interaction, which leads to the universal correlation of $T_{c}$ and resistance ratio.Comment: 16 pages plus 3 figures, revtex, 76 references, For more information, Plesse see http://www.fen.bilkent.edu.tr/~yjki