Sugarcane for water-limited environments: Enhanced capability of the APSIM sugarcane model for assessing traits for transpiration efficiency and root water supply

• Published in: Field crops research 2016-09, Vol.196, p.112-123
• Main Authors: Inman-Bamber, N.G., Jackson, P.A., Stokes, C.J., Verrall, S., Lakshmanan, P., Basnayake, J.
• Format: Article
• Language: English
• Subjects: APSIM-Sugar; Drought resistance; GxE interaction; Maximum transpiration; Transpiration efficiency
• ISSN: 0378-4290; 1872-6852
• DOI: 10.1016/j.fcr.2016.06.013

•New features added to the APSIM- Sugar module now deal with observed clonal variation in transpiration efficiency (TE).•Options for internal CO2 concentration (Ci) and vapour pressure deficit mediated responses were developed.•Biomass allocation to roots now effects root water uptake in the new module and improves its performance.•Trade-offs between water use efficiency and yield are now possible.•Over 200 observations from 38 experiments show model reliability with a priori parameterization. Genetic variation in traits affecting transpiration efficiency has been reported in sugarcane, but the impact of this variation on yield in a range of production environments needs to be estimated for assessing the priority and selection weightings to apply to these traits in crop improvement programs. A modelling approach may be useful and even necessary for reasonable assessment of these traits across production environments with different and temporally variable levels of water availability. Earlier theoretical modelling using the Agricultural Production Systems Simulator (APSIM)-Sugar module, found that traits affecting transpiration efficiency (TE) and water uptake by roots were important for improving sugarcane grown with highly variable rainfall. However, there were limitations of APSIM-Sugar in accommodating key physiological mechanisms, and this led to a revision of the APSIM-Sugar module described in this paper. Four key features were added to enable genetic variation in TE traits and root water supply (RWS) known to exist, to be modelled and assessed for predicted impact. These features were 1) the response of TE to water stress, 2) the midday flattening of hourly transpiration when plants are stressed, 3) conductance limits to hourly transpiration, which can apply even without stress and 4) the separation of soil hydraulic conductivity (k) and root length density (l) rather than the use of combined kl for determining RWS. A dataset of 182 observations of above ground biomass from 13 field experiments of sugarcane were used to check firstly that the new sugarcane module did not affect the simulation results when all the new features were disabled (model stability), secondly to check that the new features did not greatly reduce model performance, and thirdly, to determine the response or sensitivity of yields to the new features. Variation in parameter settings for the new features were based on the best evidence available for genetic variation in these tra