Capability of the ‘Ball-Berry’ model for predicting stomatal conductance and water use efficiency of potato leaves under different irrigation regimes Fulai Liu a, *, Mathias N. Andersen b , Christian R. Jensen a a University of Copenhagen, Faculty of Life Sciences, Department of Agriculture and Ecology, Højbakkagaard Alle ´ 13, DK-2630 Taastrup, Denmark b University of Aarhus, Faculty of Agricultural Sciences, Department of Agroecology and Environment, P.O. Box 50, DK-8830 Tjele, Denmark 1. Introduction Stomata play a central role in the regulation of photosynthesis and transpiration thereby the water use efficiency (WUE) of plant leaves (Jones, 1992). Biological water-saving irrigation strategies like alternate partial root-zone drying (PRD) irrigation have been developed based on extrapolating the role of stomatal control in modulating WUE, such that partial stomatal closure may increase WUE under moderate soil water deficits (Liu et al., 2005). Therefore, an accurate prediction of the stomatal conductance for water vapour (g s ) under varied environmental conditions is necessary for better irrigation scheduling thereby maximizing crop water productivity. The responses of g s to environmental factors have been intensively studied and numerous models have been developed for predicting g s (e.g. Gutschick and Simonneau, 2002 and literature cited therein). Among others, the model proposed by Ball et al. (1987) (denoted as BB-model hereafter), describing the relationship of g s to net photosynthesis (A n ), relative humidity (h s ) and CO 2 concentration (C s ) on the leaf surface, received wide attention and applications due to its apparent simplicity (Kim and Lieth, 2003). The Farquhar’s photosynthesis model (Farquhar et al., 1980) has been used for simulating A n as an input for the BB-model (Gutschick and Simonneau, 2002; Bauerle et al., 2004; Misson et al., 2004; Liu et al., 2008b). However, due to the interdependency between A n and g s , this approach has been criticized by Aphalo and Jarvis (1993) that the BB-model is not a model of g s but a model of the relationship between A n and g s , and it is of no use for defining causal relationships. Nevertheless, many authors have reported that, given a good estimation of A n or using the measured A n as an input variable, the BB-model performed successfully in predicting Scientia Horticulturae 122 (2009) 346–354 ARTICLE INFO Article history: Received 27 January 2009 Received in revised form 12 May 2009 Accepted 25 May 2009 Keywords: Solanum tuberosum L. Model simulation Partial root-zone drying Stomatal conductance Water use efficiency ABSTRACT The capability of the ‘Ball-Berry’ model (BB-model) in predicting stomatal conductance (g s ) and water use efficiency (WUE) of potato (Solanum tuberosum L.) leaves under different irrigation regimes was tested using data from two independent pot experiments in 2004 and 2007. Data obtained from 2004 was used for model parameterization, where measurements of midday leaf gas exchange of potted potatoes were done during progressive soil drying for 2 weeks at tuber initiation and earlier bulking stages. The measured photosynthetic rate (A n ) was used as an input for the model. To account for the effects of soil water deficits on g s , a simple equation modifying the slope (m) based on the mean soil water potential (C s ) in the soil columns was incorporated into the original BB-model. Compared with the original BB-model, the modified BB-model showed better predictability for both g s and WUE of potato leaves on the parameterization data set. The models were then tested using the data from 2007 where plants were subjected to four irrigation regimes: non-irrigation (NI), full irrigation (FI), partial root-zone drying (PRD), and deficit irrigation (DI) for 3 weeks during tuber initiation and earlier bulking stages. The simulation results showed that the modified BB-model better simulated g s for the NI and DI treatments than the original BB-model, whilst the two models performed equally well for predicting g s of the FI and PRD treatments. Although both models had poor predictability for WUE (0.47 < r 2 < 0.71) of potato leaves, the modified BB-model was able to distinguish the effects of the irrigation regimes on WUE being that the WUE was generally greater for PRD than for FI and DI plants. Conclusively, the modified BB-model is capable of predicting g s and of accounting for the differential effects of irrigation regimes on WUE of potato leaves. This information is valuable for further simulating potato water use thereby optimizing WUE under field conditions. ß 2009 Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +45 3533 3416; fax: +45 3533 3478. E-mail address: fl@life.ku.dk (F. Liu). Contents lists available at ScienceDirect Scientia Horticulturae journal homepage: www.elsevier.com/locate/scihorti 0304-4238/$ – see front matter ß 2009 Elsevier B.V. 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