THE INFLUENCE OF LENTIL, CANOLA, PEA AND WHEAT ON CARBON AND NITROGEN DYNAMICS IN TWO CHERNOZEMIC SOILS

Even though the sustainability of crop rotation with pulses has been demonstrated by ancient civilizations, the effects of legume crops on soil organic carbon (SOC) and soil organic nitrogen (SON) dynamics has not yet been adequately quantified in the Canadian Prairies. The main goal of this thesis was to analyze the impacts of incorporating lentil and pea in rotation with wheat on SON mineralization and the fate of recently fixed C in soil. Two soil types were analyzed in this study, a Brown Chernozem (Cz) from Swift Current SK. and a Dark Brown Cz from Scott SK. To quantify the effect of pulse crops on Nitrogen (N) gross mineralization, stable 15N isotope dilution was used and eight different crop rotations were selected (five on the Dark Brown Cz: canola-wheat, pea-wheat, pea-canola-wheat, continuous wheat without N fertilizer, continuous wheat with N fertilizer; and three on the Brown Cz: lentil-wheat, continuous wheat without N fertilizer, and continuous wheat without N fertilizer). These rotations were in the wheat phase at sampling. Additionally, lentil-wheat in the lentil phase was included. Gross N mineralization was evaluated at seeding (May 2009) and anthesis (July 2009). Mean gross N mineralization was not significantly different between crop rotations on any date. Timing of sampling (seeding versus anthesis) had the strongest effect on mineralization with mineralization rates significantly higher at anthesis than at seeding. No significant effect of the soil type was found and rotations with pulse crops had higher mineralization rates than continuous wheat only when compared to unfertilized continuous wheat. Soil N mineralization and SOC dynamic are interconnected and therefore the transformation of crop residue carbon (C) into SOC was also investigated. Lentil, canola, pea and wheat were grown in intact soil cores extracted from the field plots of the N mineralization experiment (at Swift Current and Scott) and pulse-labeled with 13CO2 in a controlled environment to trace crop residue decomposition. At the end of the labeling season (first growing season) 50% of the soil cores were destroyed to estimate root biomass with a 13C technique. Before the second growing season (without 13C labeling), 13C-enriched shoot residues were ground and incorporated into the soil. At the end of the second growing season the remaining cores were destroyed to assess the amount of remaining derived C from the root and the shoot. For both growing seasons, the soil was fractionated into water extractable organic matter (WEOM) very light fraction (VLF), light fraction (LF) and heavy fraction (HF) and the δ13C was determined for each soil fraction. For all crops, estimated root biomass production was markedly higher than estimates in the literature based on root washing and counting methods. In addition, lentil had root biomass production (0-10 cm) significantly higher than the other crops and the lowest shoot:root ratio at 2.5. Since canola produced three times more straw residue than the other crops, its shoot:root ratio was significantly higher at 13.2. At the end of the second growing season, the amount of root -derived C remaining in the VLF, LF and HF had decreased 91%, 61% and 60% respectively. No significant difference was found among crops. At the end of the second growing season on the Swift Current soil (Brown Cz), lentil had more derived C per ha-1 than wheat and on the Scott soil (Dark Brown Cz), canola and pea had more than wheat. Based on these results, the deduced transformation of plant residue C into SOC was VLF first, then LF, then HF, with all fractions contributing C to the WEOM and the WEOM transferring C back to the HF

Soil nitrous oxide and methane fluxes from a land-use change transition of primary forest to oil palm in an Indonesian peatland

Despite the documented increase in greenhouse gas (GHG) emissions from Southeast Asian peat swamp forest degradation and conversion to oil palm over recent decades, reliable estimates of emissions of nitrous oxide (N2O) and methane (CH4) are lacking. We measured soil fluxes of N2O and CH4 and their environmental controls along a peatland transition from primary forest (PF) to degraded drained forest (DF) to oil palm plantation (OP) over 18 months in Jambi, Sumatra, Indonesia. Sampling was conducted monthly at all sites and more intensively following two fertilization events in the OP. Mean annual emissions of N2O (kg N ha−1 yr−1) were 1.7 ± 0.2 for the PF, 2.3 ± 0.2 for the DF and for the OP 8.1 ± 0.8 without drainage canals (DC) and 7.7 ± 0.7 including DC. High N2O emissions in the OP were driven by peat decomposition, not by N fertilizer addition. Mean CH4 annual fluxes (kg C ha−1 yr−1) were 8.2 ± 1.9 for the PF, 1.9 ± 0.4 for the DF, and 1.6 ± 0.3 for the OP with DC and 1.1 ± 0.2 without. Considering their 20-year global warming potentials (GWP), the combined non-CO2 GHG emission (Mg CO2-equivalent ha−1 yr−1) was 3.3 ± 0.6 for the PF and 1.6 ± 0.2 for the DF. The emission in the OP (3.8 ± 0.3 with or without DC) was similar to the PF because reductions in CH4 emissions offset N2O increases. However, considering 100-year GWP, the combined non-CO2 GHG emission was larger in the OP (3.4 ± 0.3 with DC and 3.5 ± 0.3 without) compared to both the PF and the DF (1.5 ± 0.2 and 1.2 ± 0.1, respectively). The increase in peat N2O emissions associated with the land-use change transition from primary forest to oil palm plantation at our sites provides further evidence of the urgent need to protect tropical peat swamp forests from drainage and conversion

Denial of long-term issues with agriculture on tropical peatlands will have devastating consequences

Non peer reviewe

The James Webb Space Telescope Mission

Twenty-six years ago a small committee report, building on earlier studies, expounded a compelling and poetic vision for the future of astronomy, calling for an infrared-optimized space telescope with an aperture of at least $4m$. With the support of their governments in the US, Europe, and Canada, 20,000 people realized that vision as the $6.5m$ James Webb Space Telescope. A generation of astronomers will celebrate their accomplishments for the life of the mission, potentially as long as 20 years, and beyond. This report and the scientific discoveries that follow are extended thank-you notes to the 20,000 team members. The telescope is working perfectly, with much better image quality than expected. In this and accompanying papers, we give a brief history, describe the observatory, outline its objectives and current observing program, and discuss the inventions and people who made it possible. We cite detailed reports on the design and the measured performance on orbit.Comment: Accepted by PASP for the special issue on The James Webb Space Telescope Overview, 29 pages, 4 figure

Improving Soil Quality and Potato Productivity with Manure and High-Residue Cover Crops in Eastern Canada

Under intensive low residue agricultural systems, such as those involving potato (Solanum tuberosum L.)-based systems, stagnant crop yields and declining soil health and environmental quality are common issues. This study evaluated the effects of pen-pack cow (Bos Taurus) manure application (20 Mg·ha−1) and cover crops on nitrate dynamics and soil N supply capacity, subsequent potato yield, selected soil properties, and soil-borne disease. Eight cover crops were tested and included grasses, legumes, or a mixture of legumes and grasses, with red clover (Trifolium pratense L.) used as a control. Forage pearl millet (Pennisetum glaucum L.) was associated with highest dry matter. On average, red clover had 88% higher total N accumulation than the treatments mixing grasses and legumes, and the former was associated with higher soil nitrate in fall before residue incorporation and overwinter, but this was not translated into increased potato yields. Pearl millet and sorghum sudangrass (Sorghum bicolor × sorghum bicolor var. Sudanese) were associated with lower soil nitrate in comparison to red clover while being associated with higher total potato yield and lower numerical value of root-lesion nematodes (Pratylenchus penetrans), although this was not statistically significant at 5% probability level. Manure incorporation increased total and marketable yield by 28% and 26%, respectively, and increased soil N supply capacity by an average of 44%. Carbon dioxide released after a short incubation as a proxy of soil microbial respiration increased by an average of 27% with manure application. Our study quantified the positive effect of manure application and high-residue cover crops on soil quality and potato yield for the province of Prince Edward Island

Response of the Arctic Pteropod Limacina helicina to Projected Future Environmental Conditions

Thecosome pteropods (pelagic mollusks) can play a key role in the food web of various marine ecosystems. They are a food source for zooplankton or higher predators such as fishes, whales and birds that is particularly important in high latitude areas. Since they harbor a highly soluble aragonitic shell, they could be very sensitive to ocean acidification driven by the increase of anthropogenic CO2 emissions. The effect of changes in the seawater chemistry was investigated on Limacina helicina, a key species of Arctic pelagic ecosystems. Individuals were kept in the laboratory under controlled pCO2 levels o