Evaluation of Trunk or Scaffold Shrinkage in Walnut as an Indicator of Orchard Water Status

After about a decade invested in development of plant-based techniques to diagnose tree water status in orchards, midday Stem Water Potential (SWP) is being adopted at the farm level as a irrigation management tool in orchard crops such as walnut and almond. An alternative technique referred to as midday, shaded Leaf Water Potential (LWP) has also been developed for use at the farm level. Effective use of a plant-based indicator of orchard water status such as SWP has been shown to result in a variety of benefits such as improved growth in developing orchards, reduced risk of root diseases associated with over-irrigation or underirrigation and longer tree life, more consistent nut yield and quality, and water savings. However, farm level adoption of SWP has been constrained because it is considered labor intensive and monitoring must be completed during a 2 to 4 hour period occurring after 12:00 noon to attain reliable information and this limits the acreage that can be monitored with a costly pressure chamber. In response to these constraints with midday SWP and shaded LWP, researchers have been working to develop alternative plant-based methods to guide orchard water management decisions. Findings from this preliminary experiment indicate that electronic sensors referred to as LVDT sensors can be used to continuously measure trunk or scaffold diameter in walnut and provide a plant-based technique that can accurately diagnose orchard water status. Furthermore it appears that it can be automated rendering it far less labor intensive and more flexible to on-farm use than either midday SWP or midday, shaded LWP. This technology warrants further research and development in walnut.