fixation by soybeans grown with different levels of mineral nitrogen, and the fertilizer replacement value for a following crop. Can. J. Soil Sci. 82: 139-145. A field experiment was established to study the impact of added mineral N on the prediction of N 2 fixation by soybean, and the consequences for the nature of any N credit that might be used to modify fertilizer recommendations to a following non-fixing crop. Nodulating and non-nodulating isolines of soybean were grown with five rates of N fertilizer, and in a second year corn was grown in the same plots and its yield compared with a response curve. Yield, total N content, amount of N derived from soil, and fertilizer utilization of the nodulating isoline of soybean were not affected by fertilizer N. In contrast, mineral N inhibited nodulation and led to a decrease in the amount of N fixed. The balance of N in the soil was more negative for lower levels of applied N, but by the following spring the amount of mineral N in the soil was the same in all plots. The yield of corn was greater in the plots that had grown nodulating soybean than the non-nodulating isoline. The N fertilizer replacement value of 25 ± 8 kg N ha -1 resulted from a greater amount of root residues in the nodulating soybean, together with a C:N ratio that would favour faster mineralization than in the non-nodulating isoline. Une expérience au champ a été réalisé pour étudier l'impact du N mineral ajouté sur la prévision de la fixation de N 2 par le soja, et les conséquences pour la nature de l'équivalent d'engrais azoté laissé par le soja pour la culture subséquente. Isolignes de soja capables ou non de noduler ont été cultivées avec cinq doses d'engrais, et dans l'année suivante le maïs a été cultivé dans les mêmes parcelles et son rendement comparé à une courbe de réponse. Le rendement, la teneur en N totale, la quantité de N dérivée du sol, et l'utilisation d'engrais du soja nodulé n'a pas été affecté par l'engrais de N. Par contre, la nodulation a été réduite par le N mineral et la quantité de N fixée a diminuée. Le balance de N dans le sol était plus négatif pour des niveaux plus bas de N appliqué, mais au printemps suivant la quantité de N mineral dans le sol était la même dans toutes les parcelles. Le rendement du maïs était plus grand dans les parcelles qui avaient eu le soja nodulé. L'équivalent d'éngrais azoté (25 ± 8 kg N ha -1 ) a résulté d'une plus grande quantité de résidu de racine dans le soja nodulé, ainsi qu'une proportion C:N qui favoriserait une minéralisation plus rapide que dans l'isoligne non-nodulée. Assuming the average grain yield of 2.42 Mg ha -1 they estimated that the N fixed was 98 ± 32 kg ha -1 . Both these values resulted from field experiments where no N fertilizer was applied.Legumes vary in their sensitivity to the effects of mineral N in the soil either as a result of the mineralization of organic matter or of fertilizer application, on N 2 fixation. While soybean is a relatively sensitive crop, both mineral and fixed N seem to be essential for maximum...

Heavy metals far in excess of trace amounts that are required for healthy plant growth, cause harmful effects on soil microorganisms; however, studies concerning the characterization of microbial communities in mine soils are scarce. The present study is the first attempt to characterize, by means of the analysis of phospholipid fatty acid (PLFA) patterns, soil microbial community composition from a contaminated mine soil (Pb, As) subjected to different remediation technologies. A pot experiment was performed with a soil from the São Domingos mine (South of Portugal) with or without native herbaceous plants combined with the following soil treatments: control; inorganic fertilizer (NPK); inorganic fertilizer plus polyacrylate polymer; inorganic fertilizer plus organic amendment (compost); inorganic fertilizer plus both amendments (compost, polymer). The measurements of PLFA patterns were made on soil samples collected 5 months after the application of remediation treatments.The total microbial biomass and the biomass of specific groups increased notably after soil treatments, particularly those including organic amendments, and were significantly higher in presence of native plants than in the corresponding bare soils. The data also indicated that a plant cover rather than organic and inorganic treatments played the dominant role in determining the composition of the microbial community. An influence of different soil treatments on microbial composition was also observed; the effect of organic amendment being more pronounced than that of the remaining treatments. The results clearly showed the efficacy of a vegetation cover (native plants) combined with the use of organic amendment in the reclamation of this degraded mine soil.

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In this study, the different fertiliser practices of four commercial vineyards (Vitis vinifera L. cv. 'Cardinal' and cv. 'D. Maria') in southern Portugal were assessed and compared in 2002. The vineyards were established in similar soils under the same climatic conditions and additional water was supplied by drip irrigation. At harvest, the mineral composition of petioles (P, K, Mg, Ca, Fe, Cu, Zn and Mn) and quality parameters of the grapes (total soluble solids expressed as degree Brix, cluster length and weight, number of grapes, grapes weight and rachis weight) were recorded. For the 'Cardinal' cultivar, the nutritional status of the plant was correlated with growth and yield, and the greatest values for most of the parameters studied were measured at Alvisquer farm. For the 'D. Maria' cultivar, a single correlation was found between nutrient levels and growth. Shoot and cluster lengths, and grape weight were similar at all farms, though cluster weight, number of grapes and total soluble solids were smaller at Pedras than at Alvisquer or Gomeira.