Proceedings of the 18th Australian Society of Agronomy Conference, 24 – 28 September 2017, Ballarat, Australia © 2017. (http://www.agronomyaustraliaproceedings.org/) 1 Assessment of canopy growth and development for three wheat cultivars under different water and nitrogen regimes Bangyou Zheng 1 , Karine Chenu 2 , Fernanda Dreccer 3 , Greg Rebetzke 4 and Scott Chapman 1 1 CSIRO Agriculture and Food, Queensland Biosciences Precinct 306 Carmody Road, St Lucia, 4067 QLD, bangyou.zheng@csiro.au 2 The University of Queensland, Queensland Alliance for Agriculture and Food Innovation (QAAFI), 203 Tor Street, Toowoomba, QLD 4350 3 CSIRO Agriculture and Food, Cooper Laboratory, Warrego Highway, Gatton, QLD 4343 4 CSIRO Agriculture and Food, PO Box 1700, Canberra, ACT 2601 Abstract Traits related to water productivity in dryland cropping interact in multiple ways to influence final grain yield. Crop modelling can be a useful tool to address the challenge of determining how to best combine region-specific traits and develop management adaptation for specific cultivars. The Agricultural Production Systems sIMulator (APSIM) model has been developed and widely-used for diverse applications in scientific research and decision support. However, the model requires further development to accurately simulate important candidate traits associated with water productivity. To better capture differences among genotypes, APSIM needs improvement related to the modelling of canopy development as a driver of water use. Field experiments were conducted in 2015 to assess variation and covariation in traits related to water productivity, e.g. early vigour, tillering, leaf area development, water soluble carbohydrate (WSC) accumulation and transpiration efficiency. Contrasting genotypes for these traits were grown under a range of water and nitrogen regimes. Data were collected through field observation, destructive sampling and high- throughput technologies. Extensive phenotyping was used to explore patterns in canopy development and canopy structure and their impact on productivity, with particular focus on variation occurring during the vegetative stage. An improved wheat model is being developed using the Plant Model Framework in the next generation prototype of APSIM. Experiments described above, as well as previously collected datasets, are being used to develop new algorithms. The new model will be used to assess wheat traits related to water productivity across the Australian wheatbelt. Keywords APSIM, crop model, high throughput phenotyping, water productivity. Introduction Crop models can be utilised to understand how to best combine traits for target environments and assist breeding of new cultivars (Hammer et al. 2014; Chenu et al. 2017). The Agricultural Production Systems sIMulator (APSIM) model has been developed and widely-used for diverse applications in decision support for crop management, whole-farm analysis and policy development (Holzworth et al. 2014). However, the model requires further development to be able to simulate different candidate traits related to water productivity, including early vigor, tillering, canopy development, water soluble carbohydrate content and transpiration efficiency. Developing new algorithms for this purpose requires a better understanding of the intrinsic mechanisms affecting these traits under different environments and management as well as the interactions between these traits. The aim of this study was to quantify the growth and development of canopies, especially during the vegetative stage, in contrasting wheat genotypes and environments. Field experiments were conducted over two years using contrasting cultivars under a range of water and nitrogen availability regimes and sowing dates. These experiments will be used at a later stage for APSIM algorithm development. The results from 2015 of three key genotypes sown at the normal date are discussed here. Methods Wheat experiments were conducted in 2015 and 2016 at the University of Queensland Gatton Campus experimental station (27.50°S, 153.01°E). Contrasting canopies were established using two irrigation treatments (irrigation and rain-fed), two nitrogen treatments (high and low), two sowing dates (normal and late in 2015, normal in 2016) and eight cultivars. The experimental field was 54 m wide and 161 m long, and split into four blocks and 621 plots. Plots contained seven rows and were 2 m wide and 7 m long. The four