Alternative methods of estimating water deficit stress of wheat grown on undisturbed and repacked soil in drainage lysimeters

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Abstract
The effect of soil modification on changing the availability of water and the onset of crop water deficit stress in wheat was assessed during 2 drying periods. The different methods of determining the onset of stress generally agreed with each other. Differences were either related to the different parts of the canopy measured or to different physiological processes measured. Because foliage temp. was continuously monitored, the dynamic development of stress in relation to increasing soil water deficit and root growth became evident. The allowable soil water deficit at the onset of stress varied widely between soil treatments and the stage of crop growth at which deficit stress occurred. Physically modifying the soil increased plant available water by 80%. This resulted from both changes in amount of soil water stored and through a more uniformly distributed root system. Wheat growing in undisturbed soil was unable to adapt to post-anthesis stress, as frequent irrigations prior to anthesis concentrated root distribution in the upper layers.