Water relations in sugarcane and response to water deficits

Knowledge of water relations is fundamental to improved crop management in regions where irrigation is practiced or where dry conditions cannot be avoided. The objective of this review was to assess where knowledge of sugarcane water relations must be strengthened in order for progress to be made in irrigation management as well as genetic improvement and general management response to climate as well as plant and soil resources. Although past research in sugarcane water relations has been piecemeal, at least some data are available for most aspects. Knowledge about evapotranspiration in sugarcane has advanced recently to allow estimates of daily water use to be obtained from hourly weather records. Evaporation from a wider range of surface conditions (mulched or lodged crops, different row configurations) needs to be determined. Physiological water stress thresholds for irrigation have been defined for a limited range of cultivars so that irrigation can be applied differentially for expansive growth and for sucrose accumulation. This work needs to be tested across a wider range of cultivars and conditions. Manipulation of dry matter partitioning through careful timing and severity water stress clearly has large potential benefits. The mechanisms for enhanced partitioning to sucrose are documented but models need to be developed and tested to transfer this knowledge to practical irrigation management for increasing sucrose content. Responses to water stress in root and leaf conductances varied considerably between the few genotypes considered. Further research on 13C discrimination is warranted after reports of genetic variation in this trait. Osmoregulation, on the other hand, appears not to vary greatly amongst cultivars. Control of stomatal aperture by chemical signals from roots could apply to both ripening processes and to limited growth in compacted soils. This needs to be followed up.