. 2008. Nutrient budgets of Ontario organic dairy farms. Can. J. Soil Sci. 88: 107Á114. The sustainability of organic dairying in Canada, with respect to nutrients, remains unexamined. To assess how management affects nutrient status, we documented whole farm nutrient (NPK) budgets over 2 yr (2003 to 2005) and soil (0 to 15 cm) P and K status on 15 long-term Ontario organic dairy farms. Farm size, livestock density and herd productivity averaged 110 ha, 1.00 livestock units ha(1 and 5656 kg milk cow (1 yr (1 , respectively. Annual farm nutrient surpluses of 75 (N), 1 (P) and 11 (K) kg ha(1 yr (1 were lower than those reported for confinement-based dairy farms in the United States, pointing to possible environmental benefits from reduced off farm impacts on air and water quality. Weighted average soil test P levels were low (B10 mg kg ) on approximately 50% of farms, while exchangeable K levels were moderate to high (76 to 160 mg kg(1 ) on all farms. Four farms adopting a ''self-sufficient'' approach, producing most feed on-farm, imported little P as feed (1.37 to 1.90 kg P ha(1 yr(1 ) and had negative aveage farm P balances (avg. (1.54 kg P ha(1 yr(1). An integrated nutrient management approach, along with a flexible feed import strategy, fosters the sustainability of organic dairying systems. Les exce´dents annuels d'e´le´ments nutritifs a`la ferme de 75 (N), de 1 (P) et de 11 (K) kg par hectare annuellement sont infe´rieurs a`ceux rapporte´s dans les e´levages de bovins laitiers en claustration des É .-U., signe que les plus faibles re´percussions des ope´rations hors ferme sur la qualite´de l'eau et de l'air pourraient eˆtre be´ne´fiques pour l'environnement. La concentration moyenne ponde´re´e du P dans le sol e´tait faible ( B10 mg par kg) dans environ la moitie´des exploitations, alors que celle d'ions K e´changeables e´tait de moyenne a`e´leve´e partout (de 76 a`160 mg par kg). Quatre exploitations avaient instaure´une approche d'autosuffisance, la majeure partie des aliments du be´tail e´tant produite sur place avec peu d'achats de P (1,37 a`1,90 kg de P par hectare annuellement), ce qui a eu une incidence ne´gative sur le bilan du P a`la ferme (en moyenne (1,54 kg de P par hectare annuellement). Une approche inte´gre´e a`la gestion des e´le´ments nutritifs assortie d'une strate´gie suffisamment souple pour l'achat des aliments du be´tail favorise la durabilite´des e´levages biologiques de bovins laitiers.
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.
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