N2O emissions from an irrigated and non‐irrigated organic soil in eastern Canada as influenced by N fertilizer addition

Drainage and cultivation of organic soils often result in large nitrous oxide (N₂O) emissions. The objective of this study was to assess the impacts of nitrogen (N) fertilizer on N₂O emissions from a cultivated organic soil located south of Montréal, QC, Canada, drained in 1930 and used since then for vegetable production. Fluxes of N₂O were measured weekly from May 2004 to November 2005 when snow cover was absent in irrigated and non‐irrigated plots receiving 0, 100 or 150 kg N ha⁻¹ as NH₄NO₃. Soil mineral N content, gas concentrations, temperature, water table height and water content were also measured to help explain variations in N₂O emissions. Annual emissions during the experiment were large, ranging from 3.6 to 40.2 kg N₂O‐N ha⁻¹ year⁻¹. The N₂O emissions were decreased by N fertilizer addition in the non‐irrigated site but not in the irrigated site. The absence of a positive influence of soil mineral N content on N₂O emissions was probably in part because up to 571 kg N ha⁻¹ were mineralized during the snow‐free season. Emissions of N₂O were positively correlated to soil CO₂ emissions and to variables associated with the extent of soil aeration such as soil oxygen concentration, precipitation and soil water table height, thereby indicating that soil moisture/aeration and carbon bioavailability were the main controls of N₂O emission. The large N₂O emissions observed in this study indicate that drained cultivated organic soils in eastern Canada have a potential for N₂O‐N losses similar to, or greater than, organic soils located in northern Europe.     

Kinetics of acetylcholine synthesis and hydrolysis in myasthenia gravis

Kinetic studies for choline-O-acetyltransferase (CAT) (E.C. 2.3.1.6) and acetylcholinesterase (E.C. 3.1.1.7) were performed on serum, skin fibroblasts in culture, and biopsied sartorius muscle from normal and myasthenic subjects. There was a significant decrease of CAT activity per milligram of protein in myasthenic muscle compared to normal muscle, and there was no difference in acetylcholinesterase activity per milligram of protein in the same muscle homogenates. Substrate concentration curves for acetyl coenzyme A and CAT also showed a significant reduction in the maximum rate of product formation (V(max)) per milligram of protein between myasthenic and normal muscle. It is postulated that binding of substrate to CAT is being inhibited by an inhibitor present in muscle.     

PERFORMANCE OF DUALEX IN SPRING WHEAT FOR CROP NITROGEN STATUS ASSESSMENT,YIELD PREDICTION AND ESTIMATION OF SOIL NITRATE CONTENT

Dualex and SPAD are devices developed for the purpose of testing crop nitrogen (N) status. These instruments were used in a wheat experiment in order to compare their respective performance in assessing leaf nitrogen (N) concentration, response to N topdressing application, soil nitrate (NO₃)-N levels and in predicting grain yield. The experiment included different N rates in 2005 and 2006 in the Montérégie region of Quebec, Canada. Dualex readings correlated negatively with SPAD readings, leaf N concentration, soil NO₃-N content and wheat grain yield. SPAD alone and the ratio of SPAD to Dualex measurements (Chl/Phen) were linearly related to N application rate but no effect of N application rate was found for individual Dualex parameters. However, both SPAD and Dualex readings were affected by year effects. The Dualex was also capable of indirect evaluation of in-season soil NO₃-N accumulation and the prediction of wheat yield, but more so as Chl/Phen.     

Influence of photosynthetic irradiance on nitrate reductase activity,nutrient uptake and partitioning in tomato plants

The objective of the present work was to study the nutritional behavior of tomato plants (Lvcopersicon esculentum Mill.) subjected to high pressure sodium (HPS) supplementary lighting in relation to nitrate reductase activity (NRA). Tomato plants were grown with or without HPS supplementary lighting at 2 different root‐zone temperatures (RZT). Supplementary lighting combined with low RZT promoted NRA and cation uptake. Magnesium uptake appeared particularly related to the NRA daily pattern. Effects of photosynthetic irradiance (PI) at two growth stages on partitioning of 45Ca and 86Rb were also investigated. Low light level stimulated 45Ca uptake in fruiting plants but depressed 86Rb uptake. A hypothetical mechanism involving the influence of NRA and K cycling on HCO₃‐ excretion by root is proposed to explain the effects of treatments on mineral uptake.     

Spatially explicit assessment of forest road suitability for timber extraction and hauling in Switzerland

Efficient forest management, and wood production in particular, requires a forest road network of appropriate density and bearing capacity. The road network affects the choice of a suitable extraction method and the length of the transport route from the forest, while the road standard defines the truck type that can be used.

We evaluate the forest road network’s economic suitability for harvesting operations in the entire Swiss forest, an area of about 13,000 km² covering a range of topographies, based on the Swiss National Forest Inventory’s (NFI) forest road dataset. This dataset is based on information from an interview survey with the local forest services and includes all forest roads in Switzerland capable of carrying trucks. Extraction options and hauling routes are analysed together; thus, the entire logging process is examined.

Model results include maps of the most suitable extraction method; extraction costs; hauling costs; and a suitability map based on a combination of the results. While the larger part of the Swiss forest is classified as “suitable” for economic harvesting operations, significant portions also fall into the “limited suitability” and “not suitable” categories. Our analysis provides an objective, country-wide, spatially explicit assessment of timber accessibility. The resulting suitability map helps identify areas where timber harvesting is economic using the current forest road network, and where it is not. The model results can be used in road network planning and management, for example, by comparing road-network re-design scenarios, and compared to the spatial distribution of available wood volume.

     

Nitrogen fertilizer application and developmental stage affect silage quality of timothy (Phleum pratense L.)

Crop composition at harvest affects the ensiling process and the resulting silage quality. The objectives of this study were to determine: (i) the effect of annual N‐fertilizer application (0, 60, 120 and 180 kg N ha^?1) and developmental stage (stem elongation, early heading, late heading and early flowering) on the ensiling properties and silage quality of the spring regrowth of timothy (Phleum pratense L.) at two sites for 1 or 2 years, and (ii) the relationship between ensiling properties of the forage and the quality of the resulting silage. Laboratory silos with wilted forage at approximately 350 g dry matter (DM) kg^?1 of fresh matter were prepared at each harvest and opened 150 d later for silage analysis. Higher rates of N‐fertilizer application decreased the concentration of water‐soluble carbohydrates (WSC), increased the buffering capacity (BC) and nitrate concentration, and decreased the ratio of WSC:BC, primarily in the early stages of development. The ensiling properties of timothy were, therefore, less favourable when high rates of N fertilizer were applied. Silage pH generally increased with increasing rates of N‐fertilizer application; this increase was particularly evident at the first three developmental stages at one site in 1 year. Non‐protein N (NPN) and soluble N concentrations of the silages increased with increased rates of N‐fertilizer application at the first three developmental stages but decreased at early flowering. Ammonia‐N concentration in the silages increased by 0·85, 0·56 and 0·67 when rates of N‐fertilizer application were 60, 120 and 180 kg ha^?1, respectively, compared with that when no N fertilizer was applied. Significant correlations between the composition of the forage ensiled and silage quality variables were found at sites in individual years but, when all data were combined, WSC concentration and BC, and their ratio in the forages, were not correlated with pH, and soluble‐N and ammonia‐N concentrations of the silages, and were weakly correlated with NPN and free amino acid‐N concentrations of the silages. Silage quality was reduced by increased N‐fertilizer application, primarily at the early developmental stages, and this can be attributed to a reduction in WSC concentration and an increase in BC of the forage. Water‐soluble carbohydrate concentration, BC, and their ratio, however, were poor predictors of silage quality.