Le cycle de l'azote de marais filtrants artificiels : potentiel d'émission de gaz à effet de serre (GES) et exportation de formes azotées

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal

Food-Based Composts Provide More Soil Fertility Benefits Than Cow Manure-Based Composts in Sandy Soils

Nutrient concentration and availability vary substantially among composts depending on the materials used and the production process. Composts produced from agricultural operations typically utilize animal wastes such as manures, whereas composts produced in urban areas mainly incorporate food and yard waste. Our objective was to assess how different composts affect nutrient availability and cycling, mostly carbon (C) and nitrogen (N). In a laboratory incubation, we compared three composts derived from cow manure (composted dairy manure solids, vermicompost made from those manure solids, and Black KowTM) and two composts derived from food waste (composted food waste from the UF-IFAS Compost Cooperative and EcoscrapsTM). We used two sandy soils from Gainesville, FL: one from an area under perennial grasses and a second heavily-tilled soil lower in organic matter. Incubations were conducted for eight weeks at 24 and 30 °C, i.e., the annual and July mean soil temperature for the area. The composted and vermicomposted cow manure solids had the greatest CO2 emissions relative to the unamended soils. Soil nitrate was highest with composted food waste, whereas all three cow manure-derived composts resulted in lower soil nitrate compared to the unamended soils. This suggests that N was immobilized with cow manure-derived composts, consistent with the high CO2 emissions measured with these amendments. We found similar results for both soils. Our results indicate a greater potential for food-waste compost as a nutrient source than compost derived primarily from cow manure solids, which could be more beneficial to building soil C

Three years of cover crops management increased soil organic matter and labile carbon pools in a subtropical vegetable agroecosystem

Abstract Cover crops have been widely adopted to improve soil functions in agroecosystems, including providing carbon (C) inputs that can contribute to soil C sequestration. However, soil C changes may be slow after introducing cover crops in unfavorable environments for soil organic matter (SOM) accumulation, like the Southeast United States subtropical region characterized by a warm humid climate, and coarse‐textured soils. We examined labile C pools as potential early indicators of SOM changes after cover crop introduction in a sandy subtropical vegetable production system. We compared the effects of four cover crop monocultures namely two grasses [sorghum sudangrass, Sorghum bicolor × S bicolor var. Sudanese and pearl millet, Pennisetum glaucum (L.) R. Br.], two legumes (sunn hemp, Crotalaria juncea L., and cowpea, Vigna unguiculata Walp.), and one four‐species mixture on soil organic carbon pools for 3 years. Soil samples were collected at a 15‐cm depth before cover crop planting and post cover crop incorporation to assess changes in SOM, permanganate‐oxidizable carbon (POX‐C), mineralizable carbon (Cmin), and water extractable organic carbon (WEOC). The incorporation of cover crops increased concentrations of SOM, POX‐C, and Cmin in year 3 relative to their baseline values in year 1. Concentration of SOM increased by 0.24 ± 0.05% (mean ± standard error) after 3 years of cover crop management. However, concentrations of WEOC significantly decreased in years 2 and 3 relative to the baseline. Monocultures and the mixture had similar effects on measured C pools, likely due to comparable aboveground biomass production. Our findings highlight the potential of POX‐C and Cmin as early indicators of SOM accumulation driven by cover crops use, as well as the capacity of cover crops to build SOM in similar subtropical systems and coarser textured soils

Greenhouse gas production and efficiency of planted and artificially aerated constructed wetlands

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Greater Nitrogen Availability, Nitrous Oxide Emissions, and Vegetable Yields with Fall-Applied Chicken Relative to Horse Manure

Optimal manure management can maximize agronomic benefits and minimize environmental impacts. Field experiments were conducted in the Pacific Northwest (Vancouver, Canada) to determine how chicken and horse manures that were fall-applied to meet nitrogen crop demand affect soil ammonium (NH₄⁺) and nitrate (NO₃ −), apparent net mineralization (ANM) and nitrification (ANN), crop biomass and nutrient concentration, and fluxes of nitrous oxide (N₂O), carbon dioxide (CO₂), and methane (CH₄). Relative to horse manure, chicken manure increased soil NH₄⁺ by 60-fold, ANM by 2-fold, and ANN by 4-fold. Emissions of N₂O (+600%) and CO₂ (+45%) were greater and growing season CO₂ emissions (−40%) were lower after application of chicken than horse manure. Productivity of cover crop (+30%), legume cover crop (−25%), and squash cash crop (+20%) were affected by chicken relative to horse manure. Overall, fall-applied chicken manure increased yields, N availability, and environmental impacts relative to horse manure.Land and Food Systems, Faculty ofNon UBCReviewedFacult

Protection from wintertime rainfall reduces nutrient losses and greenhouse gas emissions during the decomposition of poultry and horse manure-based amendments

<p>Manure-based soil amendments (herein “amendments”) are important fertility sources, but differences among amendment types and management can significantly affect their nutrient value and environmental impacts. A 6-month in situ decomposition experiment was conducted to determine how protection from wintertime rainfall affected nutrient losses and greenhouse gas (GHG) emissions in poultry (broiler chicken and turkey) and horse amendments. Changes in total nutrient concentration were measured every 3 months, changes in ammonium (NH₄⁺) and nitrate (NO₃⁻) concentrations every month, and GHG emissions of carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O) every 7–14 days. Poultry amendments maintained higher nutrient concentrations (except for K), higher emissions of CO₂ and N₂O, and lower CH₄ emissions than horse amendments. Exposing amendments to rainfall increased total N and NH₄⁺ losses in poultry amendments, P losses in turkey and horse amendments, and K losses and cumulative N₂O emissions for all amendments. However, it did not affect CO₂ or CH₄ emissions. Overall, rainfall exposure would decrease total N inputs by 37% (horse), 59% (broiler chicken), or 74% (turkey) for a given application rate (wet weight basis) after 6 months of decomposition, with similar losses for NH₄⁺ (69–96%), P (41–73%), and K (91–97%). This study confirms the benefits of facilities protected from rainfall to reduce nutrient losses and GHG emissions during amendment decomposition.</p> <p><i>Implications</i>: The impact of rainfall protection on nutrient losses and GHG emissions was monitored during the decomposition of broiler chicken, turkey, and horse manure-based soil amendments. Amendments exposed to rainfall had large ammonium and potassium losses, resulting in a 37–74% decrease in N inputs when compared with amendments protected from rainfall. Nitrous oxide emissions were also higher with rainfall exposure, although it had no effect on carbon dioxide and methane emissions. Overall, this work highlights the benefits of rainfall protection during amendment decomposition to reduce nutrient losses and GHG emissions.</p

Nitrogen fertilization and genotype jointly drive bermudagrass (Cynodon spp.) productivity but are not associated with differences in SOC

Abstract Pastureland contributes a large share of the global soil C stock, much of which derives from root systems. Management practices like fertilization and the introduction of improved forages have clear benefits to aboveground forage production, but their impacts on belowground biomass (BGB) and hence soil C are less clear, especially in relatively understudied subtropical pastures. If fertilization and improved cultivars increase BGB, C sequestration may benefit. However, long‐term soil C stocks, and their associated ecosystem services, may be compromised if these practices sacrifice roots in favor of shoot production. We studied the aboveground and belowground biomass of nine bermudagrass (Cynodon spp.) genotypes in response to four escalating NPK fertilization rates and compared the soil C and N stocks among them. As expected, increasing fertilization improved forage accumulation (FA) although gains from additional N diminished at higher fertilization rates. A positive relationship between fertilization and BGB emerged but varied among genotypes. The latter identified potential tradeoffs between aboveground and belowground allocation in newly released and commercial forage varieties, which may affect pasture persistence and contributions to soil organic matter over time. Overall, we found subtle differences in soil organic C/soil organic N stocks among NPK fertilization rates and genotypes, with the strongest signal emerging from C isotopic analysis. Our results suggest that fertilization at the recommended rate and improved genotype selection minimized negative tradeoffs between aboveground and belowground biomass and did not elicit differences in SOC in the top 15 cm but likely contributed to ecosystem disservices as it relates to N losses

Assessing the sensitivity and repeatability of permanganate oxidizable carbon as a soil health metric: An interlab comparison across soils

Soil organic matter is central to the soil health framework. Therefore, reliable indicators of changes in soil organic matter are essential to inform land management decisions. Permanganate oxidizable carbon (POXC), an emerging soil health indicator, has shown promise for being sensitive to soil management. However, strict standardization is required for widespread implementation in research and commercial contexts. Here, we used 36 soils—three from each of the 12 USDA soil orders—to determine the effects of sieve size and soil mass of analysis on POXC results. Using replicated measurements across 12 labs in the US and the EU (n = 7951 samples), we quantified the relative importance of 1) variation between labs, 2) variation within labs, 3) effect soil mass, and 4) effect of soil sieve size on the repeatability of POXC. We found a wide range of overall variability in POXC values across labs (0.03 to 171.8%; mean = 13.4%), and much of this variability was attributable to within-lab variation (median = 6.5%) independently of soil mass or sieve size. Greater soil mass (2.5 g) decreased absolute POXC values by a mean of 177 mg kg−1 soil and decreased analytical variability by 6.5%. For soils with organic carbon (SOC) >10%, greater soil mass (2.5 g) resulted in more frequent POXC values above the limit of detection whereas the lower soil mass (0.75 g) resulted in POXC values below the limit of detection for SOC contents −1 while decreasing the analytical variability by 1.8%. In general, soils with greater SOC contents had lower analytical variability. These results point to potential standardizations of the POXC protocol that can decrease the variability of the metric. We recommend that the POXC protocol be standardized to use 2.5 g for soils <10% SOC. Sieve size was a relatively small contributor to analytical variability and therefore we recommend that this decision be tailored to the study purpose. Tradeoffs associated with these standardizations can be mitigated, ultimately providing guidance on how to standardize POXC for routine analysis.</p