Influence of plant nutrient concentration on growth rate: Use of a nutrient interruption technique to determine critical concentrations of N, P and K in young plants

Abstract

A method is described for determining the way in which growth rate varies with plant nutrient concentration using a simple nutrient interruption technique incorporating only 2 treatments. The method involves measuring the changes in growth and nutrient composition of otherwise well-nourished plants after the supply of one particular nutrient has been withheld. Critical concentrations are estimated from the relationship between the growth rate (expressed as a fraction of that for control plants of the same size which remained well-nourished throughout) and the concentration of the growth-limiting nutrient in the plants as deficiency developed. Trials of the method using young lettuce plants showed that shoot growth rate was directly proportional to total N (nitrate plus organic N) concentration, and linearly or near-linearly related to K and P concentration over a wide range; the corresponding relationship for nitrate was strongly curvi-linear. Critical concentrations (corresponding to a 10% reduction in growth rate) determined from these results were similar to critical values calculated from models derived from field data, but were generally higher than published estimates of critical concentration (based on reductions in shoot weight) for plants of a similar size. Reasons for these discrepancies are discussed. Nitrate, phosphate or potassium concentrations in sap from individual leaf petioles were highly sensitive to changes in shoot growth rate as deficiency developed, with the slope of the relationships varying with leaf position, due to differences both in their initial concentration and in the rates at which they were utilized in individual leaves. Each nutrient was always depleted more quickly in younger leaves than in older ones, providing earlier evidence of deficiency for diagnostic purposes. Although the plants were capable of accumulating nitrate, phosphate and potassium well in excess of that needed for optimum dry matter production during periods of adequate supply, the rate of mobilization of these reserves was insufficient to prevent reductions in growth rate as the plants became deficient. This brings into question the validity of the conventional concept that luxury consumption provides a store of nutrients which are freely available for use in times of shortage. The implications of these results for the use of plant analysis for assessing plant nutrient status are discussed.

Prediction and Measurement of the Decline in the Critical-K, the Maximum-K and Total Cation Plant Concentrations during the Growth of Field Vegetable Crops

“…Similar linear relationships between sub-optimal plant-K concentrations and relative growth rate have been reported by Ericsson and Kahr (1993) and by Burns (1992) although, in other studies, Burns and Hutsby (1986) found a curved relationship. W, in these latter studies, was less than 2 t ha − ".…”

“…Even so, worthwhile comparisons can be made of the maximum K concentrations in the early stages of growth. In some cases there has been reasonably good agreement but, in others, higher values than those found here have been reported (Haworth and Cleaver, 1964 ;Costigan 1985Costigan , 1986Burns, 1992). One explanation for such differences is that leaching from leaves has varied among environments, sometimes being substantial (Tukey, 1970 ;Chapin, 1980).…”

“…Support for the existence of predominantly linear relationships between plant-N concentrations and relative growth rate comes from the numerous examples referred to by A / gren (1985) and, subsequently, by Greenwood, Stone and Draycott (1990), Greenwood et al (1991) and Burns (1992). Similar linear relationships between sub-optimal plant-K concentrations and relative growth rate have been reported by Ericsson and Kahr (1993) and by Burns (1992) although, in other studies, Burns and Hutsby (1986) found a curved relationship.…”

Composition and digestibility during ageing of Italian ryegrass leaves of consecutive insertion levels

“…Nitrogen in the total herbage mass declined throughout the experiment in both treatments (Fig 1D). However, according to the criteria developed by Burns (1992), nitrogen concentration in dry matter never fell below the critical level for optimal growth.…”

Field investigations of nitrogen dioxide (NO<sub>2</sub>) exchange between plants and the atmosphere

“…Furthermore, it is known that the nutritional status influences the photochemical activity of plants (Pflüger and Mengel, 1972;Burns, 1992). For longer enclosure studies it is of interest that plant species efficiently withdraw nutrients from leaves prior to senescence Dalling, 1982, 1983;Lohman et al, 1994;BuchananWollaston, 1997).…”