Earlier harvest dates have become necessary for Canadian Christmas tree producers to meet international demand, though by harvesting these trees early they may experience poor needle retention. The objective of this study is to understand the effect of harvest date on needle retention and link those changes to cold acclimation. In one experiment, balsam fir trees with varied needle abscission resistance (NAR) were collected in October and in January and monitored for needle retention. This was repeated for 3 years. In a second experiment, 45 branches were collected each month from September to January and monitored for needle retention, xylem pressure, membrane injury, capacitance, and accumulation of galactose, raffinose, and abscisic acid. High-NAR trees had little improvement in needle retention from October to January, whereas low-NAR trees had significantly improved needle retention from October to January. Between September and January, there was an 85% increase in raffinose, 147% increase in galactose, 80% increase in abscisic acid, and 62% decrease in stem capacitance. Early harvest was not detrimental for all trees, and it appears that cold acclimation is linked to postharvest needle abscission, though cold acclimation does not adequately explain differences between NAR classes.Résumé : Les producteurs canadiens d'arbre de Noël doivent récolter les arbres plus tôt pour satisfaire la demande internationale bien qu'une récolte hâtive ait un impact négatif sur la rétention des aiguilles. L'objectif de cette étude était de comprendre l'effet de la date de récolte sur la rétention des aiguilles et de relier ces changements à l'acclimatation au froid. Dans une première expérience, des sapins baumiers dont la résistance à l'abscission des aiguilles (RAA) était différente, ont été collectés en octobre et en janvier et la rétention des aiguilles a été suivie. Ceci a été répété pendant trois ans. Dans une seconde expérience, 45 branches ont été récoltées chaque mois, de septembre à janvier, pour faire le suivi de la rétention des aiguilles, de la pression du xylème, des dommages aux membranes, de la capacité électrique et de l'accumulation de galactose, de raffinose et d'acide abscissique. Il y a eu peu d'amélioration de la rétention des aiguilles d'octobre à janvier chez les arbres qui avaient une RAA élevée mais l'amélioration était significative chez les arbres qui avaient une faible RAA. Entre septembre et janvier, le raffinose a augmenté de 85 %, le galactose de 147 %, l'acide abscissique de 80 % et la capacité électrique de la tige a diminué de 62 %. La récolte hâtive n'était pas néfaste pour tous les arbres et il semble que l'acclimatation au froid soit reliée à l'abscission des aiguilles qui survient après la récolte bien que l'acclimatation au froid n'explique pas adéquatement les différences entre les classes de RAA. [Traduit par la Rédaction] Mots-clés : abscission, sapin baumier, acide abscissique, raffinose, acclimatation au froid.

Snowmelt runoff often comprises the majority of annual runoff in the Canadian Prairies and a significant proportion of total nutrient loss from agricultural land to surface water. Our objective was to determine the effect of agroecosystem management on snowmelt runoff and nutrient losses from a long-term field experiment at Swift Current, SK. Runoff quantity, nutrient concentrations, and loads were estimated after a change in management from conventionally tilled wheat (Triticum aestivum L.)-fallow (Conv W-F) to no-till wheat-fallow and subsequently no-till wheat-pulse (NT W-F/LP) and to an organic system with a wheat-green manure rotation (Org W-GM). The conversion from conventional tillage practices to no-till increased snowmelt runoff likely due to snow trapping by standing stubble after summer fallow. Relatedly, runoff after no-till summer fallow had higher dissolved P losses (0.07 kg P ha −1 ). Replacing summer fallow with a pulse crop in the no-till rotation decreased snowmelt runoff losses and nutrient concentrations. The Org W-GM treatment had the lowest P loss after stubble (0.02 kg P ha −1 ) but had high dissolved P concentrations in snowmelt following the green manure (0.55 mg P L −1 ), suggesting a contribution from incorporated crop residues. In this semiarid climate with little runoff, dissolved reactive P and NO 3 -N loads in snowmelt runoff were smaller than those reported elsewhere on the prairies (averaging <0.05 kg P ha −1 yr −1 , and <0.2 kg NO 3 -N ha −1 yr −1 ); however, the nutrient concentrations we observed, in particular for P, even without P fertilizer addition for organic production, question the practicality of agricultural management systems in this region meeting water quality guidelines.

National inventory reporting of agricultural nitrous oxide (N2O) emissions in Canada is based primarily on measurements obtained using static chambers. In regions with cold winters and an accumulated snowpack (including Canada), these measurements tend to focus on the growing season (typically May-Oct). However, research has shown that emissions continue throughout the non-growing season (NGS) and that these account for a significant proportion of annual emissions. In the Canadian National Inventory NGS emissions currently are assumed to be adequately captured in western Canada, while they are accounted for in eastern Canada by multiplying the growing season emissions by a correction factor of 1.4. a value that was derived based on a limited number of measurements. Here we use recent Canadian studies to validate this correction factor. We collected data from available Canadian studies that measured soil N2O emissions from agricultural systems for the entire year, and determined the proportion of these emissions that occurred during the NGS. The proportion of annual N2O emissions that occurred during the NGS varied widely, ranging from -4 to 119% with a mean of 35.5%, compared to the previous estimate of 30%. Due to high variability, few differences were observed between means associated with climatic, soil and management variables. To correct for NGS N2O emissions from Canadian agricultural soils we suggest that the current correction factor for converting growing season to total annual emissions be changed from 1.4 to 1.55 and that this be used for all agricultural soils in Canada rather than just eastern Canada.

To improve the estimates of C and N inputs to soil, we developed new estimates of partitioning between the harvested portion, aboveground residue, and belowground residue for 11 major crops based on depth-adjusted root/shoot ratios and grain yield-adjusted harvest indices. We updated the mean N concentration of each partition.

Drainage water from agricultural fields with applied manure can degrade the bacterial quality of surface and groundwater. The impact of conventional tillage (CT) and zero tillage (ZT) practices on Escherichia coli (E.coli) discharge through artificially drained soils is not well understood. Consequently, two field trials were conducted during 2002-2004. The first trial involved fall applications of beef manure while the second involved spring applications of dairy manure. Both surface and subsurface drainage water were monitored in the first trial while only subsurface drainage water was monitored in the second. Under fall applied beef manure (trial 1), no differences (p>0.05) were observed in E.coli concentrations (cfu/100 ml) in combined drainage water under both tillage systems. However, during 2003-2004, subsurface drainage water under ZT had higher E.coli concentrations and loads than drainage water under CT. When the combined (surface + subsurface) annual E.coli loads were considered, CT loads were greater than ZT during 2002-2003 with an opposite situation during 2003-2004. Overall, annual E.coli loads were similar under ZT (4.7×10 10 cfu/ha) and CT (4.8×10 10 cfu/ha). Spring dairy manure application (trial 2) produced significant (p>0.03) tillage effect on E.coli loads in subsurface drainage water only during the second year. During the study period, ZT plots (1.55×10 10 cfu/ha) discharged 5× more E.coli than CT (0.23×10 10 cfu/ha). A longer duration of ZT practices resulted in higher subsurface flow volumes and subsequently greater loads of E.coli discharge in both trials.

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