Hardwood seeding root and nutrient parameters for a model of nutrient uptake.

Use of mechanistic models is an increasingly accepted way to evaluate complex processes. The Barber-Cushman model provides a means to simulate nutrient uptake once information on root system characteristics, nutrient uptake, and soil nutrient supply are developed. Objectives of this study were to determine during a growing season: (i) root growth for 1-yr-old black cherry (Prunus serotina Ehrh.), northern red oak (Quercus rubra L.), and red maple (Acer rubrum L.) seedlings; (ii) net plant increase in N, P, K, Ca, and Mg; (iii) soil solution and solid phase nutrient concentrations; and (iv) the influence of root growth and soil nutrient supply changes on nutrient uptake using the Barber-Cushman model. Seedlings were grown in pots containing A horizon soil from two forest sites. Measurements were made on five occasions during the growing season. Root growth averaged 41.5 cm d-1 for red maple compared with 28.0 and 16.7 cm d-1 for cherry and oak, respectively. Seventy-five percent of root growth occurred at the end of the growing season. Total plant N showed the greatest change (25-58%) due to soil source. Model simulations underestimated observed uptake by 31 to 99%. A clear relationship between soil solution nutrient concentration and plant uptake, an important assumption of the model, was not observed. Results indicate care will need to be exercised in the development and use of root growth and nutrient supply values in mechanistic models.

Use of a multimemory stopwatch to measure the temporal gait parameters.

Before a measurement technique is used clinically, it must be shown to be both valid and reliable. The purpose of this paper was to investigate a novel technique for measuring the temporal phases of the gait cycle using a stopwatch and slow motion video. Two healthy, young adult subjects walked at a range of self-selected walking speeds on a resistive grid walkway. The subjects were videotaped while traversing the walkway. Using video played back at slow motion and a multimemory stopwatch, two student physical therapists independently analyzed the videotapes on five separate occasions. Regression analysis was used to compare the data obtained by each of the raters with those obtained from the walkway. Measurements by both raters correlated highly with those obtained from the walkway. The results indicated a slight bias between the walkway data and the stopwatch technique, but the confidence intervals suggest that the relative timing of key events differed by less than 1%. This study shows that it is possible to get valid and reliable measures of the relative durations of the temporal gait parameters using slow motion video and a multimemory stopwatch.