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High rates of asymbiotic nitrogen (N) fixation have been measured in woody roots in temperate forests, but this rate has not been quantified in boreal forests. We studied the asymbiotic [N.sub.2] fixation associated with living and decomposing woody roots of Norway spruce (Picea abies (L.) H. Karst.) in three sites in Finland. In addition, tree species effect was studied in one site that included Norway spruce and silver birch (Betula pendula Roth.) monocultures and mixed stands. The rate of [N.sub.2] fixation measured as nitrogenase activity was affected by host tree species; spruce roots were the most active (0.67 [C.sub.2][H.sub.4] x [day.sup.-1] x [(g dry mass).sup.-1] in spruce monocultures). The activity was not statistically different in decayed and living root samples, and moisture content did not explain the observed high variability in nitrogenase activity. In a birch- spruce mixed stand, the average [N.sub.2] fixation in woody roots was 0.17 kg N x [ha.sup.-1] x [year.sup.-1], whereas in Norway spruce dominated sites, the activity ranged from 0.06 to 0.15 kg N x [ha.sup.-1] x [year.sup.-1]. The [N.sub.2] fixation in decaying and living woody roots is an important contributor to the long-term total N balance of the forest. However, the estimated rate of [N.sub.2] fixation is low compared with atmospheric N deposition. Key words: acetylene reduction assay (ARA), coarse woody debris, Picea abies, Betula pendula, forest nitrogen supply. Resume : Des taux eleves de fixation non symbiotique de l'azote (N) ont ete mesures dans les racines ligneuses en forets temperees mais ce taux n'a pas ete mesure en forets boreales. Nous avons etudie la fixation non symbiotique de [N.sub.2] dans des racines ligneuses vivantes et en decomposition d'epicea commun (Picea abies (L.) H. Karst.) dans trois stations en Finlande. De plus, l'effet de l'espece d'arbre a ete etudie dans une station oU on retrouvait l'epicea commun et le bouleau verruqueux (Betula pendula Roth.) en peuplements purs et melanges. Le taux de fixation de [N.sub.2], mesure par l'entremise de l'activite de la nitrogenase, etait influence par l'espece d'arbre hote; les racines de l'epicea etant les plus actives (0,67 [C.sub.2][H.sub.4] x [jour.sup.-1] x [(g de matiere seche).sup.-1] chez l'epicea en monoculture). L'activite n'etait pas statistiquement differente que les racines echantillonnees soient vivantes ou en decomposition. La teneur en humidite n'expliquait pas la grande variabilite observee dans l'activite de la nitrogenase. Dans un peuplement mixte de bouleau et d'epicea, la fixation moyenne de [N.sub.2] dans les racines ligneuses atteignait 0,17 kg N x [ha.sup.-1] x [an.sup.-1], tandis qu'elle variait de 0,06 a 0,15 kg N x [ha.sup.-1] x [an.sup.-1] dans les stations dominees par l'epicea. La fixation de [N.sub.2] dans les racines ligneuses vivantes et en decomposition contribue de facon significative au bilan a long terme de N total dans les forets. Cependant, le taux estime de fixation de [N.sub.2] est faible comparativement au depot atmospherique de N. [Traduit par la Redaction] Mots-cles : methode de la reduction de l'acetylene, debris ligneux grossiers, Picea abies, Betula pendula, stocks d'azote en foret., Introduction Plants require nitrogen (N) in larger amounts than any other mineral nutrient, and in boreal forests, plant-available N is generally the most growth-limiting factor (Kukkola and Saramaki 1983; Nohrstedt [...]

We analysed the timing of pesticide treatments for eventual analysis of temporal environmental risks associated with pesticide use in field vegetable crops. At the same time, we investigated whether farmers followed the Integrated Pest Management (IPM) instructions. The data cover chemical plant protection in field vegetable farms in southwestern Finland in 2009–2019. The timing of treatments, made with different pesticides in the weeks following sowing, corresponded with the known phenology of different pests of carrot, swede and fresh pea. The same was true for the carrot fly, the pea moth and the second generation of the cabbage root fly when phenological flight time models using historical data were used to predict the timing of treatments. We conclude that farmers acted in accordance with the principles of IPM when practising chemical control. For those species that lacked phenological predictive models in the study years, the degree days for the observed timing of treatments can be used as a starting point if such models are developed in the future. Our results can be used as a long-term baseline in future surveys on the changes in pesticide use and their risks regarding the studied crops. [ABSTRACT FROM AUTHOR]