Improved irrigation management

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The mapping and application of corn heat units for Saskatchewan

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Soil conditions and early crop growth as influenced by repeated swine manure application

Non-Peer ReviewedPrevious research on land applications of manures has focused on soil fertility and the relationship to final crop yield, but there is little research that quantifies the effects of changes in soil physical and chemical properties on early crop development that may ultimately be a factor in determining final yield. Surface crusting, sealing and soil strength may have significant impacts on crop emergence and early root growth that may explain final grain yield differences in some years. Research was carried out at Dixon, Saskatchewan in 2003 to examine the effect of manure addition on soil physical and chemical parameters important to crop emergence and early root development. The effects were then related to field observations made on emergence and root development of barley. This paper covers the results of this study

The three-stage petrochemical evolution of the Steens Basalt [southeast Oregon, USA] compared to large igneous provinces and layered mafic intrusions

The Steens Basalt, southeast Oregon, USA, initiated at 17 Ma as the earliest pulse of the Columbia River Flood Basalt of the northwestern USA. New and existing stratigraphically controlled data reveal temporal changes in lava flow character, and whole-rock and mineral compositions, which we use to evaluate how the balance of magma differentiation processes change in time. Temporal petrochemical variations in the Steens Basalt are analogous to the transition from Imnaha Basalt to Grande Ronde Basalt units of the Columbia River Flood Basalt and have parallels to the temporal evolution of the Deccan and Siberian traps, in India and Russia, respectively, as well as to the stratigraphic sequences of the Bushveld, of South Africa, and Stillwater, in southern Montana, USA, layered mafic intrusions. The excellent stratigraphic control from the Steens Basalt provides a detailed record for comparison across this variety of large mafic systems, providing ability to focus on commonalities among differentiation processes in time. Chemostratigraphic excursions and volcanological characteristics in the Steens Basalt record a three-stage history. A minimally exposed early stage preserved in the lower A Steens Basalt section is characterized by heterogeneity (3–8 wt% MgO) collapsing to homogeneity (~5 wt% MgO), suggesting crystal fractionation outpaces recharge. Sparse weathering horizons indicate some time elapses between eruptions. The second stage, lower B Steens Basalt, is volumetrically dominant and represents waxing of the basaltic pulse. Flows are stacked immediately upon one another without evidence of weathering or intervening sedimentary horizons, indicating high-eruptive frequency. Compositions oscillate over a ΔMgO of ~4–5 wt% between low- and high- MgO basalt, both of which become more magnesian up section, signaling a period dominated by recharge. This stage closes with declining oscillations to produce homogeneous compositions (6–8 wt% MgO). The waning stage of eruption is represented by the upper Steens Basalt section, where thin intercalated weathering horizons occur especially high in the section. The upper Steens Basalt is characterized by overall declining MgO and increasing incompatible element concentrations confirming the dominance of crystal fractionation accompanied by crustal assimilation. In detail, the upper Steens Basalt initiates with a small stack of heterogeneous flows (5–8 wt% MgO), followed by a period of relatively homogeneous flows (~6 wt% MgO) and closes with highly variable basalts to trachybasaltic andesites. These compositional characteristics coupled with a change in average flow thickness from lower to upper Steens Basalt of5–10 m illustrate a shift to more silicic compositions and higher viscosity up section. The chemical changes up section in other large igneous provinces record similar variations in differentiation processes through time, suggesting that these large volume systems share similar evolutionary histories: the earliest records suggest the magmatic systems are initially more ephemeral and compositionally variable as magma traverses relatively cool crust. With waxing, a transition to regimes of high thermal and mass input results in a stage where recharge outpaces crystal fractionation. Thermal priming of the crust during these events coupled with waning input yields magmas in which fractionation plus crustal assimilation dominates over recharge late in the system; pulses of later stage felsic magmatism in many large mafic provinces are consistent with this evolution. Using layered mafic intrusions as an analog for intrusive, cumulus-dominated residua of voluminous fractionation, as well as oceanic large igneous provinces as an analog for total magma volumes in continental flood basalt regimes, leads to the suggestion that 50%–85% of the total magma volume in a flood basalt remains in the crust, effectively remaking the crust in these regions

Changing Mantle Sources and the Effects of Crustal Passage on the Steens Basalt, SE Oregon: Chemical and Isotopic Constraints

Continental flood basalts are more prone to compositional modification from passage through thicker and (or) more felsic crust in comparison to their oceanic counterparts. The Steens Basalt in southeast Oregon (~17 Ma) is among the oldest and most mafic members of the Columbia River Basalt Group and provides a record of the early stages of flood basalt volcanism. We evaluate the balance of mantle sources in time during the onset of Columbia River Basalt Group magmatism and assess the effect of crustal passage using stratigraphically controlled Sr, Nd, Pb, Hf, Os, and O isotopic compositions, as well as whole rock major and trace element data. Mixing models indicate that depleted and enriched mantle sources identified by previous workers contribute in varying proportions during the life of the magmatic system, with the greatest contribution by depleted mantle when eruption rate and presumed intrusion rate increase. During waxing, enrichment of δ18O in some flows signals cryptic deep fractionation of abundant clinopyroxene followed by shallow fractionation of olivine ± clinopyroxene ± plagioclase. Os concentrations are among the highest worldwide at a given MgO (0.29–0.86 ppb at 6.0 to 10.9 wt.%). We argue that high Os results from scavenging of sulfides by recharging magmas passing through earlier crystallized magmas. Elevated 87Sr/86Sr in the latest stage supports modest assimilation of partial melts from mafic accreted terranes, facilitated by thermal priming of crust by persistent magmatism. This work provides a more detailed schematic view of the Steens Basalt magmatic system, from mantle origin through crustal staging

Bulk rock composition and geochemistry of olivine-hosted melt inclusions in the Grey Porri Tuff and selected lavas of the Monte dei Porri volcano, Salina, Aeolian Islands, southern Italy.

The Aeolian Islands are an arcuate chain of submarine seamounts and volcanic islands, lying just north of Sicily in southern Italy. The second largest of the islands, Salina, exhibits a wide range of compositional variation in its erupted products, from basaltic lavas to rhyolitic pumice. The Monte dei Porri eruptions occurred between 60 ka and 30 ka, following a period of approximately 60,000 years of repose. The bulk rock composition of the Monte dei Porri products range from basaltic-andesite scoria to andesitic pumice in the Grey Porri Tuff (GPT), with the Monte dei Porri lavas having basaltic-andesite compositions. The typical mineral assemblage of the GPT is calcic plagioclase, clinopyroxene (augite), olivine (Fo72−84) and orthopyroxene (enstatite) ± amphibole and Ti-Fe oxides. The lava units show a similar mineral assemblage, but contain lower Fo olivines (Fo57−78). The lava units also contain numerous glomerocrysts, including an unusual variety that contains quartz, K-feldspar and mica. Melt inclusions (MI) are ubiquitous in all mineral phases from all units of the Monte dei Porri eruptions; however, only data from olivine-hosted MI in the GPT are reported here. Compositions of MI in the GPT are typically basaltic (average SiO2 of 49.8 wt %) in the pumices and basaltic-andesite (average SiO2 of 55.6 wt %) in the scoriae and show a bimodal distribution in most compositional discrimination plots. The compositions of most of the MI in the scoriae overlap with bulk rock compositions of the lavas. Petrological and geochemical evidence suggest that mixing of one or more magmas and/or crustal assimilation played a role in the evolution of the Monte dei Porri magmatic system, especially the GPT. Analyses of the more evolved mineral phases are required to better constrain the evolution of the magma

Prolonged history of silicic peralkaline volcanism in the eastern Pacific Ocean

Socorro Island, Mexico, is an alkaline and peralkaline volcanic island located in the eastern Pacific Ocean on a mid-ocean ridge spreading center that was abandoned at ∼3.5 Ma. Silicic peralkaline rocks comprise up to 80% of the surface of the island, rendering Socorro virtually unique in the Pacific Ocean. Precise, replicate 40Ar/39Ar ages of 21 peralkaline trachytes and rhyolites reveal a history of episodic volcanic activity from ∼540 to 370 ka that may have culminated with caldera formation; repose periods between these episodes may have had maximum duration of ∼30 kyr. After up to 200 kyr of quiescence, 40Ar/39Ar ages indicate that postcaldera silicic peralkaline activity commenced by 180 ka, forming the Cerro Evermann Formation. Postcaldera mafic alkaline lavas of the Lomas Coloradas Formation erupted dominantly between 70 and 150 ka based upon relative age relations. The dominant lithology of precaldera and syncaldera silicic peralkaline deposits on Socorro is nonfragmental and nonvesicular and lacks lithic fragments and fiamme; despite this, numerous lines of evidence including welding zonation, presence of a proximal ignimbrite or co-ignimbrite deposit, association with a caldera, and compositional heterogeneity within eruptive units suggest that they are dominantly ash flow tuffs. A change in eruptive style, from predominantly explosive to predominantly effusive, followed caldera formation and suggests that a change in the efficacy of magma degassing may be linked to caldera formation. On the basis of the presence of a caldera, the magma chamber associated with Socorro Island is shallow and probably resides within the upper oceanic crust or the edifice. This together with a prolonged history of silicic magmatism indicates that intrusion of mafic magma maintained thermal viability of the magmatic plumbing system. The minimum calculated growth rate for the entire volcanic edifice (7 × 10−4 km3/yr) exceeds those of nonhotspot off-axis volcanoes in the Pacific by almost an order of magnitude. Eruption rates for subaerial phases on Socorro may be several orders of magnitude smaller than this growth rate and are comparable to subaerial eruption rates of isolated ocean islands related to mantle plumes

A simple dynamic model explains the diversity of island birds worldwide

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