Dear Abdenour Kheloufi

In a field experiment, you can take 3-5 plants from each plot at flowering or pod formation stage and measure the area of all leaves by a leaf area meter. Then calculate leaf area index (LAI) as:

LAI = leaf area (cm2) / ground area (cm2) 

Alternatively, you can measure ground green cover of each plot by viewing the canopy of plants through a wooden frame (50 cm × 50 cm), divided into 100 equal sections by thread. The sections with at least half filling with plants green area are counted and percentage of ground cover is determined without any plant destruction. In this way, you can measure ground cover at different stages of plant growth and development. There is a linear relationship between ground cover and light interception, but the relation of LAI with light interception is not linear. 

In a pot experiment, you can take one plant from each pot and measure the area of all leaves by a leaf area meter.

Regards

Kazem Ghassemi-Golezani

This is relative to Treatment effect: if it exceeds the standard error you may gain separation efficiency by Anova. In practice you never got significance with less than 4 replications http://stats.stackexchange.com/questions/13622/relationship-between-number-of-replications-and-the-standard-deviation-of-entry

Dear Colleagues,

Tahnk you very much for your suggestions. That will be very helpfull for my studies.

Cordially