Introduction
If you are an agronomist, plant breeder or ecologist on one day of your professional life you will have a plant leaf in front of you and need to know its size.
In better case it will be the only leaf but in most cases crop researchers have dozens and hundreds of leaves to how to measure leaf area.
What is the most efficient and not too expensive way to do this? How to measure leaf area effectively? What are the differences between various methods?
The cost of leaf area meter is another area of concern. It is always more difficult to find good tools if you don’t have money to buy expensive equipment.
Hence, let’s consider all these questions and find the most relevant solution for leaf area measurement with small budget.
How to measure leaf area manually?
There are a couple of methods for measuring leaf area manually. Most of these methods are a slow, laborious and not convenient to use on hundreds of leaves. However, if you have a limited number of leaf samples and you do not have any smartphone to use digital leaf area meter, then manual leaf area measurement is exactly what can help you to get the right data about your plants.
However, it’s important to highlight the existing difference in accuracy, time consumption, easiness to use and required equipment.
Let’s start with the simplest methods, available for anyone.
Millimetre Graph Paper Method
If you are doing your first leaf area measurements ever, you can try the simplest method At the same time, this method is one of trustable. It will also work smoothly with simple leaves, for example, apple, pear, spinach, etc.
At the same time, if you need to measure leaf area of compound leaves, for example, chestnut or baobab leaves, then it is better and more accurate to use mobile application, handheld leaf area meter or any other method. The same problems may have place for needle leaves, for example, pines or cedars.
Instruction How To Use Millimetre Graph Paper for Leaf Area Measurement
- Take a sheet of millimetre paper. In fact, it is possible to use squared paper like a sheet of paper from a notebook as well. However, millimetre paper will provide higher accuracy and more convenience. Otherwise, you can use 1-centimeter grid paper, which will also be a good fit.
- Place a leaf on a paper and trace the contour of a leaf with a pen or pencil.
- Count the squares inside the contour.
One square in an ordinary notebook is 0.5 cm, hence, to get square centimetre it is required to have four squares (two on top and two on bottom). Hence, if you will count the squares in the contour, divide them by 4 - this will be the area, which you need.
On millimetre paper, you will see the thinner lines, which help to identify square centimetres.
- Write down the result. If you need to count more than one leaves, it is better to put the name of the first contour, for example “Leaf no.1” and simultaneously, use the same name for the result of measurement.
- If you need to measure total leaf area for your leaves then you need to add all your measurements and write down the result.
Importantly, to use millimetre graph paper is better and more convenient than squared paper from a notebook. Basically, millimetre graph paper has one line per millimetre and it has centimetre index lines on letter-sized paper. In other words, it will be easier to count square centimetres, covered by contour.
Leaf area measurement with millimetre graph paper requires time and attention
Pros And Cons Of Measuring Leaf Area with Millimetre Graph Paper
This method is one of the oldest ways to get leaf area measurement. It is also on top of the cheapest, extremely clear and easy to use by pupils at schools as well as PhD candidates at the Universities.
However, there are two significant disadvantages. This method requires time and efforts to count squares. Hence, this brings possible errors and limited ability to measure many leaves simultaneously.
One more thing, which may serve as a disadvantage - the millimetre graph paper method ideally works with simple leaves, harvested from the plant. In other words, it may not be a good fit for non-destructive leaf area measurement of compound leaves or a big number of leaves.
Leaf area with ImageJ and other PC software solutions
There are different digital applications, which help to measure leaf area using a photo of a leaf or leaves. The main difference among them is caused by the specific technical requirements such as calibration scale on the photo. Otherwise, the price of the solution may be an additional distinctive parameter.
The most popular PC software for leaf area measurement are:
- ImageJ is a free software application with numerous modules for scientific research. One of these modules can measure area of object and is applicable to leaf area.
- Adobe Photoshop is a professional graphic editor with wide range of functions to process images. One of them helps to measure area of object and if the defined object is a plant leaf, then Adobe Photoshop can estimate leaf area.
- MatLab is a programming and numeric computing platform to analyze data. There is no available ‘ready-to-use’ module or function but it is possible to write it from scratch.
- WinFolia is a Windows-based PC application, which measures leaf area of broad leaves.
Instruction How To Use ImageJ for Leaf Area Measurement
- Make a photo of a leaf on contrast background. IMPORTANTLY: next to the leaf you must have a ruler, coin or any other object with the known scale. Without this scale you will not be able to use ImageJ for leaf area measurement.
- Open ImageJ, choose the photo and apply the scale, based on the object mentioned before.
- Find contour of the leaf, apply the scale and measure leaf area by choosing the appropriate menu.
Pros And Cons To Use ImageJ For Leaf Area
All these PC programs for leaf area measurement work with the same principle: you must have an image of a leaf. In most cases it has to be a photo of a leaf, captured by a photo camera or scanned with an office scanner.
Other steps of using this software for measuring leaf area leaves are approximately similar to described in ImageJ instruction above.
In most cases, due to the digital nature of calculations, these methods provide accurate results of leaf area measurement. At the same time the disadvantages of using ImageJ and other PC software to get leaf area are:
- Time consuming preparation, for example, to make photo or scan of leaves, to set scale and identify leaf edge, etc.
- Price of the software is high, unless it is ImageJ, which is free of charge. In other words, if you wish to use Adobe Photoshop then you need to pay monthly subscription $21 per month on yearly basis. For Matlab the price tag is from $49 to $2,150. Finally,
Every application has specific options and conditions in order to measure the leaf surface area.
How to measure leaf area automatically?
Alongside manual methods, there is a possible automatic or semi-automatic methods for leaf area measurement. The most known of them are using leaf area scanners or handheld leaf area meters. Otherwise, the applying mobile applications becomes more popular. These mobila applications are developed for plant phenotyping and measuring leaf area but also have additional functionality.
Handheld Leaf Area Meters
Leaf area meters are the handheld devices, which measure leaf area by sliding through the surface of leaf and scanning it. As a result, the leaf area measurement is available to see on the display.
Advantages and Disadvantages of Leaf Area Meters
Leaf have a wide use for non-destructive leaf area measurement.
Leaf Area Scanners can be either handhold, or portable (LI-Cor, CID, WinDIAS). You need to take a leaf area scanner with you and go to the field. This equipment provides accurate results and is comfortable to use.
But they are too expensive for an ordinary farmer or scientist. Also, they have a problem of saving data: you cannot synchronise your leaf area measurement with data cloud or your PC.
Digital Leaf Area Meters
Mobile applications. There are two known Android-based mobile apps to measure leaf area: Petiole and Easy Leaf Area. Both of them are free to download, have an affordable price and provide precise plant leaf data. The way how they work is almost intuitive: open app, calibrate the camera, place a leaf in front of a camera and press the button on the screen. The app shows leaf area measurement in square centimetres. However, Petiole goes a little bit further and provides more options for work. If you have more than one leaf area measurement, this app will show you average leaf area and also there is an option to make an experimental comparison of different leaves.
Conclusion
There are variety of methods how to measure leaf area quickly, accurately and not to spend thousands of dollars on the equipment. Advancement of digital technologies allow to use leaf area meter on regular basis anywhere. However, other methods such as millimetre graph paper method, using ImageJ or measuring leaf area with handheld leaf area meter, are also suitable alternative for solving the problem of leaf area measurement.
