Characterizing Plant Response

Non weather proofed sap flow sensor (inset) and numerous  weather proofed sap flow sensors in operation under field conditions


While developing a plant water requirement model, numerous measurements are taken. The information collected via these measurements can be used to develop an integrated systematic approach for solving water management issues within the nursery and landscape industries. Models can be adapted for a specific site by inputting readily available site specific information.  


Plant Water Use

One reason we measure plant water use is because it provides hard numbers for whole plant water use.  Various methods exists for quanitfying plant water use.  The choice of one method over another usually depends on the environment measured (indoor versus outdoor, field versus containerized, etc.).

Sap Flow Measurement System

sap flow logger

A sap flow sensor system is effective for measuring whole plant water use because it can be operated in both 

containerized and field conditions (Fig. 1). The sap flow sensor consists of a collar that wraps around the treestem.  Several different sensors within the collar relay data back to a central controller/logging device (Fig. 2).  From the data, we can calculate branch or whole plant transpiration (water use).

Unfortunately, there are several drawbacks to wide application of sap flow measurements:

  1. method is cost prohibitive
  2. technically difficult
  3. difficult to apply over great distances (e.g., separate nursery blocks of plants). 

Although the sap flow measurement method is wonderful for research purposes, it is not practical for the industry.  It is solely used to verify and refine water use models.  These models will calculate and report water use estimates.


Plant Measurement Types

cartoon tree fitted with various environmntal response     sensors

Before we can create a water use model, plant system must first be characterized. This requires monitoring of numerous plant responses in order to understand how a plant will respond to various environmental conditions.  These measurements can usually be separated into two types

  1. Dynamic and site specific - needed for on site application.
  2. Static and transferable among site - available from other sources (e.g. the internet), provided before model release.

The dynamic measurements needed for site-specific application can be automatically collected from both a weather station (e.g., temperature, humidity, light, wind speed) and a substrate moisture sensor.  Data collection is automated and costs from weather stations and substrate moisture sensors are minimal after initial purchase. 

Below we illustrate an example of how automated sensors collect weather and substrate data for model calculations (Fig. 3).  The illustration shows data collection from a single tree only, but this tree could either be an individual stand-alone tree (as in the case of a landscape setting) or among hundreds of others i.e. within a nursery stand of trees.  If it were among hundreds of others, the sensors illustrated below would not be repeated on every tree but rather placed on one or several representative trees.