Derek H. Lynch

Soil Physical Properties and Organic Matter Fractions Under Forages Receiving Composts, Manure or Fertilizer

A field study was conducted to assess the benefits, with respect to soil physical properties and soil organic matter fractions of utilizing composts from a diversity of sources in perennial forage production. A mixed forage (timothy-red clover (Trifolium pratense L.) and monocrop timothy (Phleum pratense L.) sward were fertilized annually with ammonium nitrate (AN) at up to 150kg and 300 N ha−1 yr−1, respectively, from 1998-2001. Organic amendments, applied at up to 600 kg N ha−1 yr−1 in the first two years only, included composts derived from crop residue (CSC), dairy manure (DMC) or sewage sludge (SSLC), plus liquid dairy manure (DM), and supplied C to soil at 4.6 and 9.2 (CSC), 10.9 (SSLC), 10.0 (DMC) 2.9 (DM) Mg C ha−1. Soil samples (0-5cm; 5-10cm;10-15cm) were recovered in 2000 and 2001. Improvements in soil physical properties (soil bulk density and water content) were obtained for compost treatments alone. Composts alone influenced soil C:N ratio and substantially increased soil organic carbon (SOC) concentration and mass (+ 5.2 to + 9.7 Mg C ha−1). Gains in SOC with AN of 2.7 Mg C ha−1 were detectable by the third crop production year (2001). The lower C inputs, and more labile C, supplied by manure (DM) was reflected in reduced SOC gains (+ 2.5 Mg C ha−1) compared to composts. The distribution of C in densiometric (light fraction, LF; >1.7 g cm−3) and particulate organic matter (POM; litter (>2000μm); coarse-sand (250-2000μm); fine-sand (53-250μm) fractions varied with compost and combining fractionation by size and density improved interpretation of compost dynamics in soil. Combined POM accounted for 82.6% of SOC gains with composts. Estimated compost turnover rates (k) ranged from 0.06 (CSC) to 0.09 yr−1 (DMC). Composts alone increased soil microbial biomass carbon (SMB-C) concentration (μg C g−1 soil). Soil available C (Cext) decreased significantly as compost maturity increased. For some composts (CSC), timothy yields matched those obtained with AN, and SOC gains were derived from both applied-C and increased crop residue-C returns to soil. A trend towards improved C returns across all treatments was apparent for the mixed crop. Matching composts of varying quality with the appropriate (legume/nonlegume) target crop will be critical to promoting soil C gains from compost use.

Environmental impacts of organic agriculture: a Canadian perspective.

Canada, in 2009, will enact a regulatory regime to oversee certified organic agricultural productions systems, based on a management standard. The overreaching goal of that standard is to develop farm enterprises that are “sustainable and harmonious with the environment”. However, empirical evidence to shed light on claims of environmental benefits from organic agriculture is particularly scarce in Canada and North America generally, and has not been comprehensively summarized. This review examines the literature of Canadian and US studies which relate to environmental impacts of organic agriculture within the selected indicators of: (i) soil organic matter storage and soil quality/soil health; (ii) plant and wildlife biodiversity; (iii) energy use; (iv) nutrient loading and off-farm nutrient losses; and (v) climate change and greenhouse gas emissions. The empirical evidence presented suggests organic farming system attributes regarding cropping, floral, and habitat diversity, nutrient intensity, soil man...

Impact of Land Use on Arbuscular Mycorrhizal Fungal Communities in Rural Canada

ABSTRACT The influence of land use on soil bio-resources is largely unknown. We examined the communities of arbuscular mycorrhizal (AM) fungi in wheat-growing cropland, natural areas, and seminatural areas along roads. We sampled the Canadian prairie extensively (317 sites) and sampled 20 sites in the Atlantic maritime ecozone for comparison. The proportions of the different AM fungal taxa in the communities found at these sites varied with land use type and ecozones, based on pyrosequencing of 18S rRNA gene (rDNA) amplicons, but the lists of AM fungal taxa obtained from the different land use types and ecozones were very similar. In the prairie, the Glomeraceae family was the most abundant and diverse family of Glomeromycota, followed by the Claroideoglomeraceae, but in the Atlantic maritime ecozone, the Claroideoglomeraceae family was most abundant. In the prairie, species richness and Shannons diversity index were highest in roadsides, whereas cropland had a higher degree of species richness than roadsides in the Atlantic maritime ecozone. The frequencies of occurrence of the different AM fungal taxa in croplands in the prairie and Atlantic maritime ecozones were highly correlated, but the AM fungal communities in these ecozones had different structures. We conclude that the AM fungal resources of soils are resilient to disturbance and that the richness of AM fungi under cropland management has been maintained, despite evidence of a structural shift imposed by this type of land use. Roadsides in the Canadian prairie are a good repository for the conservation of AM fungal diversity.

Improving Energy Efficiency and GHG Mitigation Potentials in Canadian Organic Farming Systems

Organic farming systems demonstrate greater energy efficiency and reduced green house gas (GHG) emissions per land unit and unit of production compared with conventional operations, usually attributable to the absence of synthetic fertilizers, particularly nitrogen, and synthetic pesticides. However, results suggest that the efficiency of organic systems can improve with research on optimizing yields/inputs, as comparisons of efficiency/output are not as robustly positive as those of efficiency/area. Organic systems also appear to have greater carbon sequestration potential. Organic systems can be significantly improved, pursuing both farm-level and sector-wide strategies. The specific conditions of organic farming, relative to conventional production, limit the number of currently promoted strategies that can fit into organic operations. Priority areas for future research to improve energy efficiency and GHG mitigation potential of organic systems are identified, including how energy crop production might be adapted to organic systems.

Organic amendment effects on tuber yield, plant N uptake and soil mineral N under organic potato production

The market for certified organic potatoes in Canada is growing rapidly, but the productivity and dynamics of soil N under commercial organic potato systems remain largely unknown. This study examined, at two sites in Atlantic Canada (Winslow, PEI, and Brookside, NS), the impacts of organic amendments on Shepody potato yield, quality and soil mineral nitrogen dynamics under organic management. Treatments included a commercial hog manure–sawdust compost (CP) and pelletized poultry manure (NW) applied at 300 and 600 kg total N ha −1 , plus an un-amended control (CT). Wireworm damage reduced plant stands at Brookside in 2003 and those results are not presented. Relatively high tuber yields (~30 Mg ha −1 ) and crop N uptake (112 kg N ha −1 ) were achieved for un-amended soil in those site-years (Winslow 2003 and 2004) when soil moisture was non-limiting. Compost resulted in higher total yields than CT in one of three site-years. Apparent recovery of N from CP was negligible; therefore CP yield benefits were attributed to factors other than N availability. At Winslow, NW300, but not NW600, significantly increased total and marketable yields by an average of 5.8 and 7.0 Mg ha −1 . Plant available N averaged 39 and 33% for NW300 and NW600, respectively. Soil (0–30 cm) NO 3 − -N at harvest was low ( −1 ) for CT and CP, but increased substantially both in season and at harvest (61–141 kg N ha −1 ) when NW was applied. Most leaching losses of NO 3 − -N occur between seasons and excessive levels of residual soil NO 3 -N at harvest, as obtained for NW600, must be avoided. Given current premiums for certified organic potatoes, improving yields through application of amendments supplying moderate rates of N or organic matter appears warranted.

Management of Canadian prairie region grazed grasslands: Soil C sequestration, livestock productivity and profitability

Lynch, D. H., Cohen, R. D. H., Fredeen, A., Patterson, G. and Martin, R. C. 2005. Management of Canadian prairie region grazed grasslands: Soil C sequestration, livestock productivity and profitability. Can. J. Soil Sci. 85: 183‐192. The GrassGro model (a computer simulation of management-induced changes in range and pasture forage and livestock productivity) was combined with spreadsheet analyses to estimate the influence of improved grazing practices on soil organic carbon (SOC), and farm profitability, across native rangelands and tame pastures of the southern Canadian Prairies. Improved practices included complementary grazing (CG) and reduced stocking density (RSD) on rangeland; and N fertilization (FERT), seeded grass/legumes grazed continuously (GLGC) or rotationally (GLGR), and RSD on tame pastures. The analysis was stratified into three ecoregions on the basis of similarities in climate and soil type. Averaged over 30 yr and ecoregions, SOC rates of gain through improved management were 5 (RSD) to 26 (CG) kg C ha ‐1 yr ‐1 for rangelands, and 86 (RSD), 75 (GLGC), 62 (GLGR) and 222 (FERT) kg C ha ‐1 yr ‐1 for tame pastures. Gains with FERT were considered largely negated by associated energy (C) costs, N 2 O emissions, and shifts in grassland species. The CG system alone improved net returns to the producer. The estimated potential combined SOC gain on prairie grazinglands (11.5 Mha) was 1.63 MMT CO 2 yr ‐1 (or 0.465 MMT C yr ‐1 ), slightly less than the 1.70 MMT CO 2 yr ‐1 currently emitted from agricultural soils in Canada.

Environmental impacts of organic agriculture in temperate regions

Can organic agriculture elaborate a scientifically based, resource-efficient and agroecological approach to low-input farm management? This review examines the literature from temperate regions, with a particular emphasis on Canadian and US studies that relate to environmental and ecological impacts of organic agriculture with respect to (i) soil organic matter storage, (ii) soil quality/soil health, (iii) nutrient loading and risks of off-farm nutrient and agrochemical losses, (iv) biodiversity and (v) energy use and global warming potential. The context and implications of semi-arid conditions and low soil P levels, common to many organic farms in North America, and widespread adoption of genetically engineered crops in conventional production, is also considered. The consensus of the data available to date indicates the distinctiveness of cropping, floral and habitat diversity, soil management regime, nutrient intensity and use efficiency, and energy, and pesticide use in organic farming confer important environmental and ecological benefits. These include maintenance of soil organic matter and added return of carbon to soil, improved soil health, reduced off-farm nitrogen and phosphorus losses, enhanced vegetative and wildlife (bird) biological diversity, extended sometimes to other taxa depending on landscape context, improved support for pollinators and pollination and reduced energy use and improved energy efficiency. The continued evolution of organic agriculture to a more outcomes-based, agroecological production system will require an expanded multi-disciplinary research effort, linked ideally to support from consumers and policy-makers on the basis of renewed understanding of its potential contribution to global environmental sustainability.

Mulch type and moisture level affect pupation depth of Rhagoletis mendax Curran (Diptera: Tephritidae) in the laboratory

Mulching can be beneficial for organic highbush blueberry production, but its effects on insect pests have received little attention. For pests that pupate in soil, depth may affect pupation success due to differences in temperature and moisture, mortality factors such as predation, or efficacy of controls such as insecticidal soil drenches. We examined how mulch type and moisture affect pupation depth for Rhagoletis mendax Curran (blueberry maggot), an important pest of blueberries. In laboratory studies, pupation depth was measured in wood waste compost, uncomposted pine needles, soil and sand, each at dry, field moisture levels and wet, 99% water holding capacity conditions. Pupation occurred more deeply but with greater variability in pine needle mulch compared to compost mulch, soil, or sand. Approximately 50% of maggots pupated on the surface of wet soil, however, maggots burrowed more deeply in wet than in dry pine needles. Moisture level did not significantly affect pupation depth in compost or sand. Some larvae unexpectedly escaped the stacks of cups used to assess pupation depth or died before forming a puparium. Less than 70% of stacks with dry pine needles contained pupae, and fewer pupae were recovered from wet than dry compost and soil. These results suggest that mulch material and/or moisture levels can have significant impacts on R. mendax pupation depth with potential implications for its management.

Avoidance tests with Folsomia candida for the assessment of copper contamination in agricultural soils

The feasibility of assessing copper accumulation in agricultural soils using avoidance tests with a Canadian strain of Folsomia candida was investigated under laboratory conditions. The avoidance response to nominal copper sulfate concentrations of 0, 200, 800, 1600 and 3200 mg kg⁻¹ in OECD soil was inconsistent between trials with the standard plastic cup or a modified Petri dish method requiring less soil. However, combined results from three Petri dish trials decreased variability and provided a 75% avoidance level, close to the 80% criterion proposed for avoidance tests. A Copper avoidance EC₅₀s of 18 mg kg⁻¹ was obtained using the Petri dish method whether tests were conducted with or without light. While Petri dish tests have potential as a cheap tool to distinguish metal contaminated soils from uncontaminated soils they would be unsuitable for tracking or quantifying changes in metal concentrations. throughout remediation. Advantages and limitations of the method have been presented.

Nitrogen Management in Organic Potato Production

There is increasing interest in organic potato production in Canada, within a context of continuing strong growth rates for organic products globally. Using data from on-farm and station based trials, key characteristics of organic potato production in the Atlantic Canada region, notably the use of extended rotations involving leguminous crop green manures combined with organic amendments, low intensity of nitrogen and residual soil mineral N (RSMN) post harvest, and enhanced soil quality and health, are shown as sustainable outcomes of these systems. Data presented confirm nitrogen as the primary factor limiting total and marketable yields. Without additional N supplementation but following legume green manures (GMr) of red clover, or hairy vetch, potato yields and N uptake are shown to range from 30 to 35 Mg ha−1 and 100–125 kg N ha−1, respectively, while RSMN remains low. Combining N supplementation (with composts or dehydrated manures) with GMr consistently increased total and marketable yield. The effect of N supply and GMr type on pest (wireworm, Colorado potato beetle) population dynamics is also examined. Finally, synchronizing N supply in these systems with crop demand remains challenging and the potential to use novel soil tests and plant bioassays to improve N management in organic production systems is also discussed.