The limit to wheat water-use efficiency in eastern Australia. I. Gradients in the radiation environment and atmospheric demand.

Book Title: NA
Year Published: 2007
Month Published: NA
Author: Rodriguez, D. ; Sadras, V. O.
Book Group Author: NA

In the wheatbelt of eastern Australia, rainfall shifts from winter dominated in the south (South Australia, Victoria) to summer dominated in the north (northern New South Wales, southern Queensland). The seasonality of rainfall, together with frost risk, drives the choice of cultivar and sowing date, resulting in a flowering time between October in the south and August in the north. In eastern Australia, crops are therefore exposed to contrasting climatic conditions during the critical period around flowering, which may affect yield potential, and the efficiency in the use of water (WUE) and radiation (RUE). In this work we analysed empirical and simulated data, to identify key climatic drivers of potential water- and radiation-use efficiency, derive a simple climatic index of environmental potentiality, and provide an example of how a simple climatic index could be used to quantify the spatial and temporal variability in resource-use efficiency and potential yield in eastern Australia. Around anthesis, from Horsham to Emerald, median vapour pressure deficit (VPD) increased from 0.92 to 1.28 kPa, average temperature increased from 12.9 to 15.2°C, and the fraction of diffuse radiation (FDR) decreased from 0.61 to 0.41. These spatial gradients in climatic drivers accounted for significant gradients in modelled efficiencies: median transpiration WUE (WUEB/T) increased southwards at a rate of 2.6% per degree latitude and median RUE increased southwards at a rate of 1.1% per degree latitude. Modelled and empirical data confirmed previously established relationships between WUEB/T and VPD, and between RUE and photosynthetically active radiation (PAR) and FDR. Our analysis also revealed a non-causal inverse relationship between VPD and radiation-use efficiency, and a previously unnoticed causal positive relationship between FDR and water-use efficiency. Grain yield (range 1-7 t/ha) measured in field experiments across South Australia, New South Wales, and Queensland (n=55) was unrelated to the photothermal quotient (Pq=PAR/T) around anthesis, but was significantly associated (r2=0.41, P<0.0001) with newly developed climatic index: a normalised photothermal quotient (NPq=Pq.FDR/VPD). This highlights the importance of diffuse radiation and vapour pressure deficit as sources of variation in yield in eastern Australia. Specific experiments designed to uncouple VPD and FDR and more mechanistic crop models might be required to further disentangle the relationships between efficiencies and climate drivers.

Pages: 287 - 302
URL: http:////,ip,url,cpid&custid=s4640792&db=lah&AN=20073092806&site=ehost-live
Volume: 58
Number: 4
Journal: Australian Journal of Agricultural Research
Journal ISO: NA
Organization: NA
Publisher: NA
ISSN: 0004-9409

crop yield, cultivars, photosynthesis, plant waterrelations, radiation, simulation models, sowing date, temperature,transpiration, vapour pressure, water use efficiency, wheat, Australia,New South Wales, Queensland, South Australia, Victoria, Triticum,Triticum aestivum, Australasia, Oceania, Developed Countries,Commonwealth of Nations, OECD Countries, Australia, Triticum, Poaceae,Cyperales, monocotyledons, angiosperms, Spermatophyta, plants,eukaryotes, carbon assimilation, carbon dioxide fixation, cultivatedvarieties, vapor pressure, Field Crops (FF005) (New March 2000), PlantPhysiology and Biochemistry (FF060), Plant Water Relations (FF062),Meteorology and Climate (PP500), Mathematics and Statistics (ZZ100)

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