Water stress and reduced fruit size in micro-irrigated pear trees under deficit partial rootzone drying
Mark G. O’Connell A B and Ian Goodwin AA Department of Primary Industries, Private Bag 1, Tatura, Vic. 3616, Australia.
B Corresponding author. Email: mark.oconnell@dpi.vic.gov.au
Australian Journal of Agricultural Research 58(7) 670-679 https://doi.org/10.1071/AR06306
Submitted: 23 October 2006 Accepted: 22 March 2007 Published: 26 July 2007
Abstract
Crop water relations, vegetative and reproductive growth, and soil water status were studied during 2 seasons to determine the effectiveness of partial rootzone drying (PRD) in a mature micro-irrigated pear orchard in the Goulburn Valley, Australia. PRD treatments were 50% (PRD50) and 100% (PRD100) of predicted crop water requirement (ETc) applied on one side of the tree alternated on a 14-day cycle compared with a Control treatment, which received 100% of ETc irrigated on both sides of the tree. Irrigation was applied daily by micro-jets to replace ETc estimated using reference crop evapotranspiration (ETo) and a FAO-56 crop coefficient of 1.15 adjusted for tree size. The PRD50 regime applied 174–250 mm for the season v. 347–470 mm for both the Control and PRD100 treatments. Irrigation maintained a well watered rootzone under the emitter compared with the drying profiles of the alternated wet/dry irrigated zones of the PRD treatments. There was no significant benefit of PRD100 compared with the Control irrigation regime. Similar vegetative growth (canopy radiation interception), reproductive growth (fruit growth rate, final fruit size, yield), fruit quality (total soluble solids, flesh firmness), and crop water relations (midday leaf conductance, midday leaf and stem water potential) were measured between the Control and PRD100. Trees under the PRD50 regime showed symptoms of severe water stress, that being greater fruit drop, reduced fruit size, lower yield, reduced leaf conductance, and lower leaf and stem water potential. The 50% water saving afforded by PRD50 led to a yield penalty of 16–28% compared with the Control and PRD100. PRD50 fruit failed to meet commercial cannery requirements due to poor fruit size. We conclude from an agronomic basis that deficit PRD irrigation management is not recommended for micro-irrigated pear orchards on fine-textured soils in the Goulburn Valley, Australia.
Acknowledgments
The technical support and assistance of Jim Selman, Neil Penfold, and Yinghong Wang is gratefully acknowledged. Financial support was provided by the STI Project 1.3.1 ‘Next generation sustainable production systems—Megabucks from Megalitres’, NPIRD Project CDH2 ‘Improving the water use efficiency of horticultural crops’, and the Department of Primary Industries. Finally, thanks to Dr Horst Caspari for his helpful comments on the manuscript.
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