Plant Stress FAQ
What is plant stress?
Plant stress contains the measurements acquired from trunk dendrometers. Trunk dendrometers measure the tiny changes in the thickness of the tree trunk that occur as the trunk swells from water at night and loses water during the day. The values can indicate stress or lack of stress in the plant.
What data points are available?
Map Tags. The tags on the map are color coded according to stress level: Green is no stress, Yellow is moderate stress, Red is high stress.
Plant stress is an index that indicates how much stress the plant is under. Stress is graded as no stress (Green), Moderate stress (Yellow), and High stress (Red). While more complicated than this simple explanation, a rough way to understand the plant soil index is that the more the tree shrinks during the day the greater the stress will be.
Trunk Displacement is the raw data retrieved. From the dendrometer. It records the actual shrink and swell of the trunk throughout the day and night.
How should I use the Plant Stress Index?
Research using dendrometers is not extensive, and shows inconsistencies. Because of this, it is best to use it as a support for other, more proven and reliable data sources such as soil moisture and ET. As you use and compare the data you will likely find ways that it is useful to you. Here are some suggestions on how you can use the data.
Setting irrigation thresholds. Because soils vary, the point at which irrigations should occur is not the same for every soil. By allowing a soil to dry until the Plant Stress index crosses from green to yellow, and comparing that to the soil moisture content at that same time, you can get an idea of the soil moisture % when the plant begins to stress. It would be wise to set your irrigation point slightly higher than that point.
Induced stress. Many crops have periods where moderate stress is beneficial to the crop or the development of the canopy. During these periods you can take advantage of the dendrometers by allowing the plant stress index to venture into the moderate stress region. This will allow you to provide some stress, but not so much as to cause damage.
Deficit irrigation. When water supply is limited, optimal use of available water can be achieved by allowing moderate stress but not high stress.
How should I use Trunk Displacement?
Plant Stress is calculated the day after the measurements are collected. Trunk Displacement, on the other hand, is close to real-time. You can use it to estimate the effects of irrigation the day of.
In general, Trunk Displacement should show an overall increase over a season. However, during periods where stress is desired, that increase should stop or be minimal, showing that sufficient stress is being applied to get the desired results.
What else should I know?
While all are based on the same initial research, each company that provides a Plant Stress Index has put their own proprietary touch on the calculations. Semios has performed extensive work to improve the model by making changes that make the index more consistent throughout the entire spectrum of wet to dry as well as reducing the effect that rain has on the measurement.