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What is Leaf Area Index?

Leaf area index, or LAI, is a metric growers use 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 in a m2 of surface.

What does the leaf area index tell us?

Growers use leaf area index to gauge the amount of photosynthesizing biomass. It’s a great proxy for understanding the flow of water, nutrients and carbon in an ecosystem. Which is why it helps with adjusting humidity and temperature control systems in greenhouses and indoor growing facilities.

On a global scale, scientists use LAI in climate models to learn about processes affecting the entire ecosystem and atmosphere, such as radiation uptake, precipitation, and energy conversion.

How to measure LAI

Leaf area index (LAI) represents how many layers of foliage can cover 1 square meter.  Values usually range from 1 to 4.5. The coefficients for radiation absorption in the plants don’t change in a ratio of 1:1 compared to the LAI. The reason for that is that in modern agriculture, growers grow crops in rows, so they don’t get light uniformly and equally from all directions. Also, leaves on the lower part of the plant tend to be less active. When comparing to younger leaves, we can see calcium accumulation on these lower, older leaves.

leaf area index (LAI) table

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. You can set traps on the ground to collect the falling leaves. After collecting the leaves, you can measure the LAI 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. When it comes to crops, however, growers use direct methods 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. You can then determine the LAI using different methods to analyze the photograph. 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.

leaf area index measurement

Why should you measure LAI 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.

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