leaf area index
Fig. 2 - LAI indicates the number of layers
the leaves from a plant could make on
the surface of the soil where the plant
is growing. For example, a LAI of three
means the soil could be covered three
times over by the leaves of a plant if they
were laid on the ground.
INDIRECT MEASUREMENT OF LAI
Indirect measurement is the typically preferred way to compute LAI. Not
only is it much easier and quicker, but non-contact measurement tools
such as plant canopy analyzers and hemispherical photography calculate
LAI in non-destructive ways. No matter if they’re measuring a plant, a
crop, or a section of a forest, plant canopy imagers quickly provide digital
information indicating the LAI with good practical accuracy. Light meters
can also be useful for measuring the LAI of individual plants or small crops.
(The amount of light that is intercepted by plant foliage before it reaches
the ground is also at the heart of LAI, though it isn’t the only consideration.)
The meters are placed at strategic locations, and their measurements are
compared against known available light measurements. This technique
basically measures intercepted light.
LAI AND PLANT HEALTH
So, now that we know what LAI is and how to calculate it, the next
question is: why would we want to measure it and what can it do for
our crop production or plant health? Leaf area index is used to predict
photosynthetic production and evapotranspiration, estimate a crop’s water
demand, calculate a plant’s estimated carbon absorption, and evaluate
theoretical production ecology. It is also a way to analyze crop growth and
the success of a growing strategy, especially in comparison to previous
seasons. For example, if a crop is a quarter way into its growth cycle and
its LAI is notably lower than the
same crop was at the same time in
“INDIRECT MEASUREMENT IS THE
a previous season, this indicates
something needs correcting.
Anything—available light, soil
moisture, nutrition, pests, disease,
WAY TO COMPUTE LAI.”
and even greenhouse layout—
could be the cause of these growth
rate changes. So, the discovery of a decrease like this should trigger the
search for the cause. If found, a remedy or solution can be applied to stay
on track for maximum yields. The earlier in the seasonal growth cycle an
adjustment or treatment is made, the more effective it can be.
typically preferred
LAI AND FRUITING CROPS
Obviously, when growing a crop that produces leaves for consumption
(spinach, for example), maximum LAI is the goal. However, LAI is also
important for fruiting crops as leaf density is often the goal during their
early stages of growth (later in that plant’s crop cycle, some amount of
thinning can enhance the size and amount of fruit produced).
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grow cycle