Values for the various fluxes of nitrogen through the tree–soil system were calculated using models derived from measurements of rates of input, accumulation, and transfer in plots of 11-m-tall Pinusnigra var. maritima (Ait.) Melv. that were showing growth responses to varying rates of nitrogen fertilizer. As the result of continuing immobilization in trees and humus, growth of the unfertilized trees was declining and the trees were having to sacrifice older tissues to mobilize sufficient nitrogen for new growth. In the fertilized trees, there was similar mobilization but of excess nitrogen stored during the period that fertilizers were applied. Models of the flux of nitrogen, phosphorus, calcium, and magnesium at optimum growth showed that tight cycling and low rates of immobilization, coupled with effective retention of relatively high atmospheric inputs, probably represents the adaptive mechanism that enables trees to thrive on soils low in potassium and magnesium. However, high rates of immobilization and low rates of atmospheric input relative to tree uptake mean that despite the maintenance of tight cycles, the trees continued to make significant demands on soil reserves of nitrogen, phosphorus, and calcium throughout their life cycle.

. 1997. Effects of three fertility amendments on soil dehydrogenase activity, organic C and pH. Can. J. Soil Sci. 77: 281-283. An Acadia silty clay and a Pugwash sandy loam were each fertilized with three rates of either composted chicken manure, fresh chicken manure, or synthetic fertilizer. The effects of these amendments on soil microbial activity (dehydrogenase enzyme activity, DHA), organic C and pH were monitored. The sandy loam soil, which was relatively high in organic C, did not experience increases in DHA due to organic amendments while compost produced higher DHA than manure or fertilizer treatments to the silty clay soil. There was no treatment effect on soil organic C in the sandy loam, while organic treatments increased organic C in the silty clay soil. Soil pH was affected by treatments to both soils with compost amendments producing the greatest increases in this parameter. The results emphasize the importance of considering initial soil organic C and soil texture when planning studies of the effect of organic amendments on soil microbial activity. Le loam sableux, relativement riche en C organique, ne manifestait pas d'intensification de la DHA due aux amendements organiques, mais dans l'argile limoneuse le fumier composté donnait lieu à une plus forte DHA que le fumier frais ou que la fumure minérale. Aucun traitement n'avait d'effet sur la teneur en C organique dans le loam sableux, mais dans l'argile limoneuse un accroissement était observé dans les traitements avec amendements organiques. Le pH des deux sols, était touché par tous les traitements, le fumier composté provoquant les plus forts accroissements. Ces observations mettent en relief l'importance de la prise en compte à la fois de la teneur initiale de C organique dans le sol et de la texture du sol dans la planification des recherches sur les effets des amendements organiques sur l'activité microbienne du sol.Mots clés: Déshydrogénase, fumier composté, fumier de volaille frais, pH, carbone organique du sol Beginning in the summer of 1991, a 3-yr experiment was initiated to assess the impacts of fresh and composted chicken manure and ammonium nitrate as N sources for established hay crops. Various soil and plant parameters, including soil pH, organic carbon and DHA, were measured for the 3 yr [for a full report on the experiment's influence on all soil and plant parameters, refer to Warman and Cooper (1994)]. Microbial activity and its related factors were of particular interest because in systems which use organic fertility sources, it is the microbial turnover of soil organic matter which determines nutrient flow to the crop. Goyal et al. (1993), for example, reported that soils with higher levels of organic C have larger pools of microbial biomass which affect the flux of plant nutrients and the size of the plant nutrient pool.The DHA is considered one of the better indicators of microbial activity because dehydrogenases only occur within living cells, unlike other enzymes which can occur in an extracellular state. However, inter...

An experiment was conducted in 2000 to compare simple visual estimate, sward height and rising plate meter (RPM) methods for determining forage biomass in mixed-species, naturalized, rotationally grazed dairy and beef pastures. Measurements were taken pre-and post-grazing on 10 sampling dates at the dairy pasture, and post-grazing at 13 sampling dates at the beef pasture. For each sampling date, the effectiveness of each method for estimating the actual biomass from a quadrat was evaluated using regression analysis. The results for the visual estimate method were not consistent, with non-linear relationships occurring early and late in the season. While the meter stick was most effective in the dairy pasture, the RPM was most effective in the beef pasture. Species composition and structural characteristics of the stand were important factors affecting accuracy of biomass estimation. Equations developed for each method and site using data from all dates had low R 2 -adjusted values, and were unreliable predictors of biomass. The results from individual sites and dates were extremely variable, with no single method effective in all circumstances. To estimate forage biomass in mixedspecies, naturalized pastures, standard quadrat harvesting remains the most reliable method, provided that enough quadrats are clipped to adequately represent a given area.

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Warman, P. R. and Cooper, J. M. 2000. Fertilization of a mixed forage crop with fresh and composted chicken manure and NPK fertilizer: Effects on dry matter yield and soil and tissue N, P and K. Can. J. Soil Sci. 80: 337-344. An experiment was conducted for 3 yr to compare the effects of fertilization of mixed forage with fresh and composted chicken manure and inorganic NPK. Fertility amendments were applied each year at three N levels and an unfertilized treatment was included. The experiment was conducted in two hay fields near Truro, Nova Scotia. Dry matter yield and forage N, P and K contents are reported for the 1992 and 1993 seasons. The nutrient content of the amendments as well as the efficiency of P and K use are discussed. Soil Mehlich 3-extractable P and K and KCl-extractable N were measured at two depths in September 1993. By the final year of the experiment, compost amendments produced yields as high as the recommended rate of NPK fertilization at both sites on both harvest dates. Medium rates of compost application also resulted in tissue N levels as high as or higher than the equivalent NPK treatments. The medium rate of manure application was equivalent in yield and tissue N to the compost treatments at the Acadia site, but had slightly lower yields and tissue N content at the Pugwash site. Compost P and K were relatively inefficiently used by the forage; this resulted in increased levels of Mehlich 3-extractable P and K in the 0-to 15-cm layer of the compost-amended plots. It was concluded that fertilization with compost or inorganic NPK, supplying equal amounts of N, can result in comparable yields and quality of forage. Dans la dernière année de l'expérience, le fumier composté donnait lieu à des rendements fourragers comparables à ceux obtenus à la dose recommandée de fumure minérale NPK, aux deux emplacements et pour les deux dates de récolte. Les doses moyennes d'é-pandage sous forme compostée produisaient des concentrations de N dans le fourrage au moins aussi hautes que la fumure minérale NPK équivalente. L'effet de la dose moyenne d'épandage de fumier frais sur le rendement et sur les concentrations azotées du fourrage équivalait à celui du fumier composté à l'emplacement Acadia, mais à Pugwash les rendements et les concentrations de N du fourrage étaient légèrement inférieurs à ceux obtenus avec le fumier composté. Le P et le K apportés dans le compost étaient relativement mal valorisés par les cultures fourragères, ce qui se manifestait par une augmentation des concentrations de P et de K extractibles dans la solution Mehlich-3 dans les 15 premiers cm du sol des parcelles traitées au compost. On peut conclure que la fumure sous forme de fumier composté ou d'engrais minéral NPK fournit des quantités semblables de N et permet d'obtenir des rendements fourragers comparables, en quantité et en qualité.