Soil P Status and Nitrogen Fixation on Organic Dairy Farms in Ontario and Nova Scotia

Legumes are a key source of nitrogen (N) in organic production systems. However, there is evidence that reduced inputs may be leading to deficient soil phosphorus (P) on some organic dairy farms (Roberts et. al. 2008). This may affect crop performance and N fixation in forage legumes. This study aims to gauge the relationship between soil P dynamics in organic dairy systems and legume biological nitrogen fixation (BNF). The study has two main sub-projects: 1. A field survey of soil-test P and legume forage productivity and N fixation on dairy farms in Ontario and Nova Scotia, Canada. 2. Growth chamber and greenhouse studies examining: a) The role of P nutrition in legume growth and N fixation, and b) The P-supplying power of composts, struvite, and a rock P source. Field data was commenced in the 2008 season, and was completed in 2009. Growth chamber and greenhouse studies were conducted in 2009. Analyses of 2009 samples are not complete at the report date

Decomposition of wheat straw and stabilization of microbial products

Includes bibliographical references (pages 74-77).This research examined the effects of soil environment on the decomposition of cereal crop residues and stabilization of microbial products in the field. Microplots at semi-arid and subhumid field sites were amended with 14C-, 15N-labelled wheat straw and with 14C-labelled glucose plus 15N-labelled NH4NO3 and the fate of the residual C and N was monitored over 10 yr. Mineralization of C and N derived from wheat straw was greater at the site in the more moist environment in the short term (2 yr). In the long term (up to 10 yr), however, the residual C and N at this site decayed at a slightly slower rate, providing evidence of stabilization of organic material in chemically resistant forms, as compared to possible physical protection in the semi-arid clay-textured soil. The total recovery of labelled N was 22.5–24% in the harvested crops with 13.4–16% remaining in the surface soil by the end of the study. Mineralized labelled organic N was used with an efficiency ranging from 32 to 51%. However, after summer fallow the crop apparently used mineralized labelled N with an efficiency of only 7%. This study showed that moistness of the soil environment has a considerable effect on residue decomposition. Stabilization of humic material derived from residues relates more to the recalcitrance of microbial products and their interactions with soil mineral colloids than to the nature of the original residue

Effect of Carbon Dioxide Concentration on the Growth Response of Chlorella vulgaris Under Four Different Led Illumination

This experiment examined the growth response of Chlorella vulgaris exposed to CO2 concentrations increasing from ambient to 8.5% and under white, blue, red and red-blue lights after 15 days incubation. Biomass production increased with increasing CO2 concentrations under all light sources. The highest biomass production, 1.59 g L-1, was obtained when the algae were supplied with 8.5% CO2 and exposed to white light. Biomass production under blue, red and red+blue light was 1.53 g L-1, 0.45 g L-1 and 1.27 g L-1, respectively. The research suggests that C. vulgaris is not able to adapt production of its photosynthetic pigments to absorb light sources different that it is normally has evolved to

Bilan phosphore du sol et fixation de l'azote dans fermes laitières biologiques de l'Ontario et de la Nouvelle-Écosse

Les légumineuses sont une source importante d'azote (N) en production biologique. Toutefois, il est prouvé que de trop faibles intrants peuvent entraîner une carence de phosphore du sol (P) dans les fermes laitières biologiques (Roberts et coll., 2008), et une réduction possible du rendement des cultures et de la fixation de N par les légumineuses fourragères. La présente étude vise à évaluer le lien entre la dynamique du P du sol et la fixation de l’azote par les légumineuses en gestion biologique (BNF). L’étude a deux principaux sous-projets : 1. Étude sur le terrain de la concentration du P dans le sol, et rendement des légumineuses fourragères et fixation de N dans les fermes laitières de l’Ontario et de la Nouvelle-Écosse, Canada. 2. Études en chambre de culture et en serre du : a) Rôle nutritif du P dans la croissance des légumineuses et dans la fixation de N. b) Taux d’apport de P des composts, de la struvite et d’une source de phosphate naturel. La cueillette de données sur le terrain, commencée à la saison 2008, a été complétée en 2009. Les études en chambre de croissance et en serre ont été menées en 2009. À la remise du rapport, les analyses des échantillons de 2009 ne sont pas terminées

Carbon sequestration potential of a 27-year-old tree-based intercropping system in southwestern Ontario

Paper presented at the 13th North American Agroforesty Conference, which was held June 19-21, 2013 in Charlottetown, Prince Edward Island, Canada.In Poppy, L., Kort, J., Schroeder, B., Pollock, T., and Soolanayakanahally, R., eds. Agroforestry: Innovations in Agriculture. Proceedings, 13th North American Agroforestry Conference, Charlottetown, Prince Edward Island, Canada, June 19-21, 2013.This study aimed to quantify carbon (C) pools and fluxes in a 27-year-old tree-based intercropping (TBI) system as compared to a conventional agricultural system at the University of Guelph�s Agroforestry Research Station (43o 16�N 89o 26�W) (established 1987). Tree species quantified during this study include poplar hybrid (Populus spp.), Norway spruce (Picea abies), red oak (Quercus rubra), black walnut (Juglans nigra), and white cedar (Thuja occidentalis). In the TBI system, above- and belowground biomass, along with soil organic carbon (SOC) concentrations, litterfall, litter decomposition and soil respiration were quantified. In the conventional agricultural field, SOC, litter decomposition and soil respiration were quantified. Preliminary results indicated higher C sequestration potential rate with faster growing species such as poplar, and slower potential rate for slower growing species such as spruce and cedar. SOC accumulation was highest in the predominant wind direction (east), closest to the tree rows (0.5 m), and at shallower depths (10-20 cm) for all species. SOC accumulation was highest under poplar tree, followed by spruce, oak and walnut. Quantities of litterfall followed similar pattern and decomposition rates are still being analyzed. Soil respiration rates were higher in TBI systems and at distances closer to the tree row. Further results will be presented on the total measured C pools and fluxes and the importance of C sequestration potential of a 27-year-old TBI system to sequester atmospheric C and mitigate climate change. Accumulation of SOC can also have implications on crop yields and long term stability of TBI soils.Amy Wotherspoon (1), Idris Mohammed (1), Naresh V. Thevathasan (1), Andrew M. Gordon (1), and R. Paul Voroney (1) ; 1. School of Environmental Sciences, University of Guelph, Guelph, ON, Canada, N1G 2W1.Includes bibliographical references

How significant to plant N nutrition is the direct consumption of soil microbes by roots?

The high degree to which plant roots compete with soil microbes for organic forms of nitrogen (N) is becoming increasingly apparent. This has culminated in the finding that plants may consume soil microbes as a source of N, but the functional significance of this process remains unknown. We used 15N- and 14C-labelled cultures of soil bacteria to measure rates of acquisition of microbes by sterile wheat roots and plants growing in soil. We compared these rates with acquisition of 15N delivered as nitrate, amino acid monomer (l-alanine) and short peptide (l-tetraalanine), and the rate of decomposition of [14C] microbes by indigenous soil microbiota. Acquisition of microbe 15N by both sterile roots and roots growing in soil was one to two orders of magnitude slower than acquisition of all other forms of 15N. Decomposition of microbes was fast enough to account for all 15N recovered, but approximately equal recovery of microbe 14C suggests that microbes entered roots intact. Uptake of soil microbes by wheat (Triticum aestivum) roots appears to take place in soil. If wheat is typical, the importance of this process to terrestrial N cycling is probably minor in comparison with fluxes of other forms of soil inorganic and organic N

SUSTAINABILITY OF ORGANIC DAIRYING IN CANADA

The distinctive production characteristics and economic performance of organic dairy farms in central Canada has been documented, but the sustainability of these systems with respect to farm nutrient flows is less well understood. We have assessed farm management, livestock productivity, and nutrient status of fifteen long term (>10y) certified organic dairy farms in Ontario, Canada. Farm size, herd size and herd productivity averaged 110 ha, 52 cows and 8207 kg milk cow yr-1, respectively. Cropping composition differed little between farms, with pasture and forage accounting for an average of 65% of the cropped landbase. Annual farm nutrient budgets (inputs-outputs) over two years (2003-2005) for N, P and K were 52, 1 and 11 kg ha-1 yr-1, respectively. The majority (13) of farms had positive K budgets with half of the farms recording negative annual P budgets. Nutrient budget results were supported by soil fertility data generated by sampling 80% of farm fields (n=225). Overall, these results contrast strongly with large nutrient surpluses reported for more intensive, confinement-based dairy farms throughout N. America, but suggest a challenge to remain sustainable over the longer term for the 50% of these farms adopting a broadly ‘self-sufficient’ approach, and importing little P (0 - 2.5 kg ha-1 yr-1) as feed and feed supplements

Greenhouse gas mitigation potential of annual and perennial dairy feed crop systems

Dairy production constitutes a significant amount of the total global anthropogenic greenhouse gas (GHG) emission. One of the proposed strategies to mitigate GHG emission from dairy production is by enhancing soil carbon sequestration through promoting the growing of perennial over annual dairy feed crop. We determined the net ecosystem carbon budget (NECB) of a hay and corn field grown side-by-side over three years to compare the GHG mitigation potential of perennial over annual feed crops in Elora, Ontario, Canada. The NECB was determined using measurements of net ecosystem exchange (NEE), total plant carbon content, and carbon content in applied dairy manure. The greenhouse gas balance (GHGB) were determined using the NECB plus the total nitrous oxide (N2O) fluxes measured by a complementary study at the same site. The effect of plowing of the hay field on the NECB and GHGB was also investigated. Our observations indicate that on average over the three study years, NECB of hay (7 ± 51 g C m−2 yr−1) was significantly lower than corn (154 ± 79 g C m−2 yr−1) indicating that corn was a larger carbon source than hay. The three-year average GHGB of 796 and 127 g CO2-eq m−2 yr−1 for corn and hay, respectively, indicated that corn was a larger emitter of GHG than hay. The NECB was the more dominant factor than N2O emissions in influencing the outcome of the annual GHGB. We conclude that hay has a larger potential than corn in sequestering carbon and mitigating GHG emission even when emissions from hay plow-down are included

Ensemble Identification of Spectral Bands Related to Soil Organic Carbon Levels over an Agricultural Field in Southern Ontario, Canada

The recent use of hyperspectral remote sensing imagery has introduced new opportunities for soil organic carbon (SOC) assessment and monitoring. These data enable monitoring of a wide variety of soil properties but pose important methodological challenges. Highly correlated hyperspectral spectral bands can affect the prediction and accuracy as well as the interpretability of the retrieval model. Therefore, the spectral dimension needs to be reduced through a selection of specific spectral bands or regions that are most helpful to describing SOC. This study evaluates the efficiency of visible near-infrared (VNIR) and shortwave near-infrared (SWIR) hyperspectral data to identify the most informative hyperspectral bands responding to SOC content in agricultural soils. Soil samples (111) were collected over an agricultural field in southern Ontario, Canada and analyzed against two hyperspectral datasets: An airborne Nano-Hyperspec imaging sensor with 270 bands (400–1000 nm) and a laboratory hyperspectral dataset (ASD FieldSpec 3) along the 1000–2500 nm range (NIR-SWIR). In parallel, a multimethod modeling approach consisting of random forest, support vector machine, and partial least squares regression models was used to conduct band selections and to assess the validity of the selected bands. The multimethod model resulted in a selection of optimal band or regions over the VNIR and SWIR sensitive to SOC and potentially for mapping. The bands that achieved the highest respective importance values were 711–715, 727, 986–998, and 433–435 nm regions (VNIR); and 2365–2373, 2481–2500, and 2198–2206 nm (NIR-SWIR). Some of these bands are in agreement with the absorption features of SOC reported in the literature, whereas others have not been reported before. Ultimately, the selection of optimal band and regions is of importance for quantification of agricultural SOC and would provide a new framework for creating optimized SOC-specific sensors