Leaf area index (LAI) is a dimensionless quantity that categorizes the plant canopy. It is defined as the one-sided green leaf area per unit ground surface area which formula is ;
( LAI = LEAF AREA / GROUND AREA, M2 / M2)
It is very useful parameter to find out the plant canopy in research. There are various methods to find LAI . Most often , the students and teachers use the device like LAI meter or Scanner to find the leaf area and they divide the value with the ground area covered by those leaves. But the matter of fact those expensive devices are not easily available. So most of the tyro in the research field found out the leaf area by the manual method using graph to find the area of irregular surface as in the picture below.
But this method is too burdensome and wasting your fruitful time. But you do not need to worry if you have well operating computer which are easily accessible to every researchers in present context.
Following are the steps I suggest you to do if you are truly willing to work faster.
1. To find the leaf area index, First step is to the find the leaf area. To find leaf area, we have to find all the leaf surface area along with it’s petiole.
2. Now , we should have to pluck all leaf of a plant with its petiole. Leaf with the attached petiole should be plucked.
3. Put the leaf on the white paper . Draw a standard (2 * 2 cm2 or desired area) rectangle on the same paper .
4. Take the scan or picture of this paper along with the standard rectangle and a leaf with petiole. Then open this picture (.jpg) with Adobe Photoshop.
#Note : We should have Adobe Photoshop already installed in your computer.
5. After you have opened the Photoshop, then select the leaf using lasso tool.
6. Then go to window option in the Photoshop and select the histogram. Then click on the double headed arrow or on the histogram, then select the expanded view and show statistics option thereby. Refresh the histogram once and note down the pixel value of selected leaf.
7. Then do the same operation for the standard rectangle you have drawn . For this you can use the rectangle marque tool which is easy for the selection of rectangular items . This tool is just above the lasso tool. Note down the pixel value for the standard rectangle.
8. Now it’s the time to finish the operation using calculator which is also available in the computer. Let’s do simple unitary method.
For the standard box with 4 cm2 ( that I have drawn ) = 147810 pixels
For the irregular surface area leaf ( that I have chosen) = 808870 pixels
Then do ,
Using simple unitary method, Area of leaf surface (A1) = (Pixels of a leaf / pixels of rectangle box ) × Area of standard rectangle.
I got A1 = 10.9 cm2. But you have calculate for all the leaf and sum all the values of leaf area to calculate leaf area index.
You can find the ground area for a plant easily which corresponds to the spacing area . Or you can use the formula Ground area of a plant (A2) = ( Total Area / No of plants )
So,
LEAF AREA INDEX = Σ A1 / A2
Credit - Roshan Dhakal, B.Sc. Ag, AFU, Rampur.