March 18, 2019
March 13, 2019
Leaf Area Index (LAI), which is used as a measure in hundreds of studies on forests, crops, climate and the environment, is calculated as half the area of all leaves per unit area of ground. It is measured as the leaf area (m2 ) per ground area (m–2) and is unit-less. So, a plant with a LAI of 2 has an amount of leaves that can cover a given area two times. LAI is calculated for a plant or can be scaled up to give readings for a whole crop or even a region. It is one of the most important parameters to measure leaves and their activity.
The significance of the LAI comes from the importance of leaves to the plants, which are many and varied.
Leaves are the major eco-physiological parts of a plant that interact with the atmosphere,
Leaves are an important source of carbohydrates produced during photosynthesis, which are converted to a myriad of chemicals that the plant needs.
The Leaf Area Index is thus an important indicator of radiation and precipitation interception, energy conversion, and water balance. Ultimately, it is a reliable parameter for plant growth. This is the reason why most studies in agronomy and horticulture measure the results of interventions such as fertilizers and irrigation in terms of LAI, as well as yield.
The levels of LAI will vary with the canopy architecture, which depends on the cultivars, geography, and field cultural practices. Then there are differences which arise from the types of crops and fruits. More is known about the optimum LAI for cereals than fruits. LAI for:
Since leaves are essential for photosynthesis and produce the bulk of biomass, the number of leaves (and LAI) will also influence yield. Moreover, most crop simulation models will use LAI to predict yield, given its importance in estimating the effect of environmental factors on plants.
The relationship between LAI leaves and yield is, however, not simple, and will vary with kinds of crops and at different life-stages of a plant. Therefore, LAI could be measured in different phases of the plant cycle to accurately calculate the optimum yield. Comparisons of LAI between different years is a good way to judge how well the crops are doing.
The trade-off between leaf growth and fruit production has assumed added relevance due to climate change. Due to the increasing levels of carbon dioxide (CO2), many cultivars are devoting too much of their resources to making leaves rather than seeds. In soybeans, the fourth most cultivated seed crop, there has been a decrease of 8% to 10% in yield due to recent conditions of elevated CO2.
LAI can be measured directly or indirectly. In direct methods, the leaves are used as the basis of measurement.
This method of LAI estimation is time-consuming and difficult, as it involves collecting leaves and measuring leaf area. The leaves can be collected:
The leaf area is estimated by three means:
Indirect LAI calculation can be non-contact, fast, and automated, and is, therefore, gaining popularity.
Besides its uses in measuring crop growth and as an indicator of yield, LAI is finding new applications in precision agriculture. LAI can be useful in calculating the correct amounts of foliar sprays of pesticides or fungicides that are needed to protect a crop. LAI can also diagnose the nitrogen status of cereals through satellite imagery leading to timely applications of fertilizers to boost yield. Given its importance, it is not surprising that new methods of estimating LAI are growing, coupled with novel purposes to monitor crops.
Science Writer, CID Bio-Science
Ph.D. Ecology and Environmental Science, B.Sc Agriculture
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Photo courtesy of Jomesh P A.