DOI: 10.4228/zalf.dk.91
title: Manual leaf area measurement on individual sugar beet plants taking plant density and irrigation into account

description: For sugar beet growth models, knowledge of the development of the photosynthetically active leaf apparatus with its up to more than 50 individual leaves per beet plant as a source of assimilate production is very important. Because the measurement using leaf area index (LAI) meters from above allows only a limited measurement and does not cover the total leaf area of all existing individual leaves, it is necessary to carry out manually leaf area measurements for individual sugar beet plants over the whole growth period without destroying the leaves. For this reason, a special measuring methodology was developed and applied. On the experimental fields of the Research Centre for Soil Fertility Müncheberg (FZB Müncheberg) (location: 52°01`N, 14°07`E, 14°07`Eastern latitude; location type: D 2a; soil type: sandy-loamy soil; German soil quality index: 26; average (1951-1981) annual precipitation: 544 mm; average (1951-1981) annual temperature: 8.2°C) leaf area measurements were carried out in different experiments with sugar beets between 1979 and 1982. In each experimental variant, the leaf areas of 8 individual plants were measured between emergence and harvesting of the sugar beet at intervals of approximately 7 days. Between end of May and mid-October usually about 20 measurements were realized. The leaf area is given in cm2 per sugar beet plant. Experiments with different crop densities (60,000, 80,000 and 100,000 sugar beet plants per hectare) as well as without and with irrigation (based on pen evaporation or based on model-added irrigation scheduling system EDV-BB) were taken into account.
description: T​o measure the leaf area per beet, each newly grown leaf (except the two cotyledons) is given a serial number. More than 50 leaves can be formed per beet. For this purpose, each petiole is given a label with a number hanging on a string. This is necessary in order to be able to identify each leaf by its number and in order to be able to document the process of growing of each individual leave. In order to improve the overview, the number is removed from leaves that have died in the process of beet development. The existing photosynthetically active (green) leaves are individually measured with a ruler taking into account their length and their width. The leaf length is measured as the distance between the beginning of leaf formation on the leaf stem and the top of the leaf. The width of the leaf is measured at its widest point with a ruler. The measuring instructions for width and length are shown in the illustration. Based on measured leaf width (W, cm) and leaf length (L, cm) the area of each leaf (A, cm²) is calculated using the following relationship: A= W x L x 0.675 . The sum of the leaf areas of all existing individual leaves gives the leaf area of a beet plant per measuring day. The factor of 0.675 was statistically determined on the basis of several hundred individual leaves of different ages and from different stages of plant development by measuring the leaf length and the leaf width and by area counting of the leaf based on a leaf projection on graph paper. For each variant of a sugar beet experiment, 8 beet plants are randomly selected from the cropping stand, whose leaves are measured non-destructively at intervals of approx. 7 days with regard to length and width.