Leaf area index, or LAI, is used to measure the amount of foliage in canopies. It is determined by the coverage of leaves per unit of the ground surface. Or in simpler terms, LAI measures how many layers of leaves are found in a m2 of surface.
What does the leaf area index tell us?
Leaf area index is used to gauge the amount of photosynthesizing biomass. Making it a great proxy for understanding the flow of water, nutrients and carbon in an ecosystem. It also helps with adjusting humidity and temperature control systems in greenhouses and growing facilities.
On a global scale, LAI is used in climate models to learn about processes affecting the entire ecosystem and atmosphere such as radiation uptake, precipitation, and energy conversion.
How is LAI measured?
The leaf area index (LAI) can be calculated by how many layers of foliage can cover 1 square meter. The values usually range from 1 to 4.5. The coefficients for radiation absorption in the plants doesn’t change in a ratio of 1:1 compared to the LAI. The reason for that is that in modern agriculture, plants are grown in rows, and do not get the light uniformly and equally from all directions. Also, leaves on the lower part of the plant tend to be less active. When compared to younger leaves, we see calcium accumulation on these lower, older leaves.
There are two approaches to measuring the leaf area index, directly or indirectly.
Direct methods require a physical collection of leaves. In deciduous species, this is relatively easy. Traps are set on the ground to collect the falling leaves and may then be measured using a leaf area meter or an image scanner.
The use of direct methods in non-deciduous plants is destructive, as leaves need to be harvested. In crops, however, direct methods are widely applied post-harvest.
Indirect methods to estimate LAI use hemispherical photography, also known as canopy or fisheye photography. This is a photograph taken upwards, from below the canopy. The image may then be analyzed using different methods to determine the LAI of the photographed area. There is a variety of equipment that does so automatically.
Indirect measurements of leaf area index are prone to inaccuracies and tend to slightly underestimate the true LAI.
Why should LAI be measured in a greenhouse?
Measuring the leaf area index in an agricultural setting provides significant knowledge of the scope of processes happening in the growing space.
A good estimation of LAI will allow growers to gauge, much more accurately, the flow of nutrients, water and gases in the growing facility. Making it possible to provide precisely what the crops need.
This allows climate control systems such as dehumidification to be tailored effectively to the amount of transpiration occurring, reducing the need to overheat or over-invest in infrastructure, due to a lack of information on what is truly going on.