During the early establishment phase, outplanted white spruce (Picea glauca (Moench) Voss) and jack pine (Pinus banksiana Lamb.) seedlings are vulnerable to lethargic growth or mortality because of interspecific competition for soil nutrients, particularly N. Accurately quantifying the degree of N competition is essential for supporting effective vegetation management (VM) decisions. This study evaluated the use of in situ burials of ion-exchange membrane (IEM; Plant Root SimulatorTM-probes) for quantifying differences in soil N supply rate between different VM treatments and the relationship of this N availability index to early growth of conifer seedlings at four boreal forest sites. At most sites, the effect of noncrop N uptake on soil N availability was apparent, with smaller NH4+-N, NO3–-N, and total dissolved inorganic N (DIN) supply rates in control plots than in VM plots. Total DIN supply rate was correlated (R2 = 0.60 to 0.73, P < 0.01) with seedling height, root-collar diameter, and stem volume growth. Ammonium-N supply rate was better correlated than NO3–-N supply rate with conifer seedling growth, which is in agreement with preferential NH4+-N uptake by conifer species. The results of this study support the use of in situ burials of IEM for measuring soil N availability during the early establishment phase.

Corresponding author (Brian.Fowler@usask.ca).Abbreviations: DL critical , critical day length; FLN, number of leaves produced on the main stem before transition to the reproductive stage; GDD, growing degree days; LT, low temperature; LT 50 , temperature at which 50% of a population is killed in an artificial freeze test; MFLN, minimum final leaf number; PP strength , strength of photoperiod genes; T c , daily mean crown temperature; T i , threshold induction temperature; V req , vernalization requirement; VR, vernalization saturation in the revised model; VRT, vegetative to reproductive transition.

An interactive web‐based model (https://norstar.usask.ca/survivalmodel) that simulates winter survival in cereals has been developed for use by farmers, extension workers, plant breeders, and researchers. Consistent with our current understanding of low‐temperature (LT) gene regulation, the model is based on a series of equations describing phenological development, acclimation, dehardening, and damage due to LT stress. Low‐temperature tolerance is estimated on a daily basis relative to crown temperature, stage of phenological development, and cultivar LT tolerance potential. Acclimation proceeds until the start of the reproductive growth stage, which becomes a critical developmental switch that initiates the downregulation of LT tolerance gene expression. Environmental data can be uploaded and model input parameters revised to allow for simulation of genotypic differences and environmental conditions of special interest to users. Because the model is fully interactive, it can be used as a teaching tool that allows production risks, cause‐and‐effect processes, and genetic theories to be systematically investigated. In addition to encouraging more widespread use of the model, opening access to interested researchers will serve as a means of additional testing and validation allowing further refinements to be made. This will hopefully lead to increased prediction accuracy over a wider range of environmental conditions and a better understanding of the dynamic interactions involved in over‐winter survival of winter annual crops.

A new extraction method for the HPLC-UV determination of metsulfuron in soil was developed and compared with NaHCO3extraction and a lentil bioassay technique. The new procedure consisted of metsulfuron extraction using anion exchange membranes followed by a dichloromethane concentration of the membrane eluates. Three soils representing different landscape positions were spiked with metsulfuron to yield concentrations in the range of 0 to 40 μg kg−1dry soil and were analyzed by the above procedures. At a given spike rate, the efficiency of the anion exchange membrane extraction was highest for the soil from the upper slope position and lowest for the soil from the lower slope position, indicating that the amount of ion-exchangeable sulfonylurea was affected by soil properties. Similar trends in degree of root growth inhibition were observed for lentil response to metsulfuron presence in soil; percent root growth inhibition was related to the landscape position as the amount of membrane-extractable metsulfuron. The percent shoot growth inhibition was not soil dependent and did not differ among soils. The efficiency of NaHCO3extraction for metsulfuron did not vary with soil type; in the NaHCO3method, because of the buffered alkaline nature of the extraction, differences in soil properties, particularly soil pH, would have less effect on metsulfuron recovery. Because of similar trends for the results of the membrane extraction method and a lentil root bioassay, anion exchange membrane extraction may provide useful information on bioavailable fractions of sulfonylurea herbicides in soil.

,Z. 1996. Assessing plant-available potassium in soil using cation exchange membrane burial. Can. J. Soil . We assessed a method for extraction of plant-available potassium using a cation exchange membrane (CEM)