Declining soil‐test phosphorus (STP) levels on eastern Canadian organic dairy farms is a concern because of potential negative impacts on forage growth and biological nitrogen fixation (BNF). This study examined the relationship between STP, forage productivity, and BNF on organic or transitional‐organic dairy farms in Ontario (ON) and Nova Scotia (NS). More than two‐thirds of 28 legume–grass mixed forage fields in the study were low in available P by provincial soil‐test guidelines. Averaged across all fields over 2 yr, forage legume proportion was 46%, forage harvested 5.9 Mg ha–1, BNF 64 kg ha–1, and N harvested 153 kg N ha–1. Forage tissue P concentrations were clearly correlated with STP in the low soil‐test categories (<10 mg Olsen P kg–1 of soil in ON; <30 mg Mehlich‐3 P kg–1 of soil in NS), above which there was little response. Inclusion of soil total P or organic P did not improve the fit of regressions. However, STP explained a very small fraction of variation in forage harvested and BNF. Ninety percent of tissue P concentrations were above 2 g P kg–1 of tissue, a frequently cited critical minimum, and the only apparently P deficient forage crops were on fields that received no manures or fertilizers for more than 5 yr. In the term of this study, low STP was apparently not having a significant impact on forage harvested or BNF on the majority of eastern Canadian organic dairy farms. This result may not apply to seedling‐year forages or other crops.

The effects of feeding total mixed ration (TMR) or pasture forage from a perennial sward under a management intensive grazing (MIG) regimen on grain intake and enteric methane (EM) emission were measured using chambers. Chamber measurement of EM was compared with that of SF 6 employed both within chamber and when cows grazed in the field. The impacts of the diet on farm gate greenhouse gas (GHG) emission were also postulated using the results of existing life cycle assessments. Emission of EM was measured in gas collection chambers in Spring and Fall. In Spring, pasture forage fiber quality was higher than that of the silage used in the TMR (47.5% v. 56.3% NDF; 24.3% v. 37.9% ADF). Higher forage quality from MIG subsequently resulted in 25% less grain use relative to TMR (0.24 v. 0.32 kg dry matter/kg milk) for MIG compared with TMR. The Fall forage fiber quality was still better, but the higher quality of MIG pasture was not as pronounced as that in Spring. Neither yield of fat-corrected milk (FCM) which averaged 28.3 kg/day, nor EM emission which averaged 18.9 g/kg dry matter intake (DMI) were significantly affected by diet in Spring. However, in the Fall, FCM from MIG (21.3 kg/day) was significantly lower than that from TMR (23.4 kg/day). Despite the differences in FCM yield, in terms of EM emission that averaged 21.9 g/kg DMI was not significantly different between the diets. In this study, grain requirement, but not EM, was a distinguishing feature of pasture and confinement systems. Considering the increased predicted GHG emissions arising from the production and use of grain needed to boost milk yield in confinement systems, EM intensity alone is a poor predictor of the potential impact of a dairy system on climate forcing.

. 2007. Assessing the energy potential of agricultural bioenergy pathways for Canada. Can. J. Plant Sci. 87: 781-792. We assessed agricultural bioenergy pathways using existing and newly developed life cycle energy analyses so as to compare the potential of these pathways to replace fossil fuel in Canada. Energy gains after subtracting life cycle fossil energy inputs (E g ) and the ratio of fuel energy to life cycle fossil energy input (ER) were calculated. Results varied widely, reflecting differences in regional yields and study assumptions. Grasses and coppiced willow processed to electricity and heat exhibited Egs of 29-117 GJ ha -1 yr -1 and ERs of 4-17. These crops processed to lignocellulosic ethanol showed E g s of 22-114 GJ ha -1 yr -1 and ERs of 5-13. Grain ethanol and oilseed biodiesel showed E g s from -15 to 32 GJ ha -1 yr -1 and ERs from 0.8 to 3.7. Assuming 20% of Canada's cleared agricultural land could be dedicated to annual biofuel crops, grain ethanol or oilseed biodiesel could displace up to 10 or 50%, respectively, of national road gasoline or diesel demand. If instead 40% of cleared agricultural land could be dedicated to perennials, the feedstocks could displace up to 52% of road gasoline demand if processed to lignocellulosic ethanol or 100% of utilities' and industries' fossil fuel demand for electricity and steam production. Our analyses showed that a goal of fossil fuel displacement favors the production of perennial crops for electricity and heating.

The soil carbon (C) accumulation rate was determined for switchgrass, as compared with selected C3 species in Nova Scotia, Canada. There was no significant effect of crops on total soil C retention, whereas soil 13C signature (δ13C) was enriched by 0.4‰ in switchgrass relative to other C3 species, and C accumulation rate was 0.06 Mg ha−1 yr−1 in the top 30 cm of soil.