Quantifying canopy formation processes in fodder beet (Beta vulgaris subsp. vulgaris var. alba L.) crops

• Canopy parameters in fodder beet were quantified across water and N supply.
• Base temperature was 0 °C and critical LAI range (90–95% interception) was 3–4 m2/m2.
• The phyllochron was estimated at ∼50 °Cd and the extinction coefficient 0.74.
• Water stress enhanced leaf senescence but reduced appearance and expansion rates.
• N stress reduced leaf expansion but had negligible effect on appearance and senescence rates.

Fodder beet is a highly productive forage crop of expanding use in livestock production systems in temperate regions, notably in Europe and New Zealand. The main determinant of fodder beet productivity is the amount of light intercepted by the crop canopy, which is regulated by temperature and the availability of water and nitrogen (N) for plant development and growth. The quantitative understanding of canopy formation processes under constraining growth conditions is an essential step for the development of biophysical simulation models of new crops for research and predictive purposes. In this study, we provided the first estimates of key canopy formation parameters in fodder beet both under optimum and water- and N-limited supply, in two field experiments in Lincoln, Canterbury, New Zealand. Specifically, the base temperature for leaf appearance in fodder beet was estimated as 0 °C. The range of the critical LAI (c. 90–95% of light interception) was 3–4 m2/m2. The phyllochron was 48–53 °Cd/leaf in unstressed crops and 60 °Cd/leaf in water stressed crops, with no effect of N supply. Leaf senescence rates varied widely (from 42 to 260 °Cd/leaf) depending on water availability and canopy cover. Leaf expansion, appearance and senescence rates fully recovered following a period of water stress to values similar to those observed in unstressed crops in response to late season rainfall events. Leaf area expansion rates (LAER) ranged from 0.0012 to 0.0034 m2/m2/°Cd and was reduced both by limited water and N supply. Leaf area senescence rates (LASR) ranged from 0.0005 to 0.0019 m2/m2/°Cd, with low values recorded during drought periods when crop growth was negligible. Canopy architecture, characterised by the extinction coefficient (k), was less sensitive to water stress than canopy expansion or senescence with a conservative value of 0.74. This first quantitative description of fodder beet canopy forming processes can assist the development of predictive approaches, such as biophysical simulation models, for application in research, extension and teaching.