Leaf area index (LAI) is a key variable used in horticultural studies involving the relation between crop growth and yield. This variable can be a very useful tool when looking to evaluate the performance of your crop.
What is LAI?
LAI represents the structural attributes of the leaf components estimated by the area of leaf per unit of ground surface area. This variable can represent the space available for photon interception which can obviously affect yield.
LAI can be an indicator of canopy health or development because it can affect how light moves through the canopy. In addition, LAI can affect the canopy surrounding microclimate. Radiation from the sun or lamps is intercepted by leaves affecting transpiration and by consequence latent heat. Radiation can also affect leaf surface temperature and by consequence surrounding air. When we recognize the relation between canopy, leaf area, and surface we can get very useful information about plant response and identify how different variables can affect or promote plant growth.
How to measure LAI?
LAI measurement can sometimes be a time-consuming process, depending on the method used. In order to measure LAI, we can use direct and indirect methods.
Direct methods can be in situ or destructive. Destructive methods involve removing leaves from the plant to make direct measurements or the use of scans in order to calculate leaf area using different software. In order to directly calculate LAI we must use the following formula:
Leaf area (m2)/ Ground area (m2) = m2/m2
Direct methods can involve direct measurements on the leaf. In order to simplify the process we can also assume a specific geometric figure in order to simplify the process. For example, in tomatoes we can measure length and width in order to get an idea of an average leaf area in the plant. Ground area is based on plant density.
Indirect methods can be done using a variety of sensors working within a software with the capability to infer LAI using measurements involving light transmission, absorption and/ or reflection of light through the canopy. Here are some examples of sensors and softwares available to estimate LAI: Licor LAI-2000 Plant Canopy Analyzer, Digital images, WinSCANOPY analysis system and PAR (photosynthetically active radiation) interception mapping method
How can I use LAI?
LAI provides information about plant response to different environmental variables. For example, if measuring variables such as: Net photosynthetic rate, transpiration or more. You can use the data and look for interaction between LAI and the variable measured in order to get information about how different variables can be affecting or promoting plant growth and/ or yield.
Why should you measure LAI in a greenhouse?
- Can provide information about your crop needs
- Can provide information to evaluate new methods or new management to improve production
- Can tell you about microclimate and system management necessities.
- Can provide information about plant transpiration / water use / humidity.
- Can be directly related to yield
LAI is one of the most important surface state variables required for a better understanding of many plant processes: Crop growth, Gas exchange, Energy and Water balance, etc…LAI can even be used to study how pests and diseases affect and spread in a crop.
Remember! The more you measure the more you can manage! A system better understood will always be a system with better results!