**6. Conclusions**

188 Solar Radiation

overall estimate of extinction coefficients for various crops based on the angle distribution of their leaves; considering average values for crops with leaf angles that were mainly almost

The method of estimation of LAI was applied on four crops: Tobacco, pepper, soybean and eggplant. The crops chosen for evaluation sought validation of the method in species with very different morphological architectures, both in distribution and area occupied by the plant, as well as the height of it. It turned to be an exponential relationship between the results derived from photography method and leaf area calculated with the planimeter. Linear correlation coefficients obtained for the various crops were 0.89 for eggplant, 0.91 for pepper, soya and 0.87 to 0.88 for tobacco (Figure 13). The correlations obtained in this evaluation were quite heterogeneous despite the morphological disparity and architecture of the different species tested, yielding correlations above 0.87 in all cases. In the case of crops of eggplant, pepper and tobacco, the growth of the canopy crop growth and leaf area occurred at the same time, the highest percentage agreeing with the largest canopy leaf area indices. This dynamic growth was not followed in the case of soybean, where the plant develops its canopy in great haste once covered. The development was apical exponential until reaching a constant height. Therefore, the feasibility of this approach is restricted to the early stages of soybean development, until it reaches the highest percentage of land shaded.

> y = 0.0058x1.3241 r 2 = 0.896

> > y = 0.0973e0.0374x r 2 = 0.8735

0 20 40 60 80 100 **PGC (%)**

0 20 40 60 80 100 **PGC (%)**

0

Fig. 13. Relationship between leaf area index (LAI) estimated through the destructive sampling of biomass and the percentage of shaded ground measured (PGC) by the

**LAI**

1

**LAI**

2

horizontal, the values obtained ranged between 0.50 and 0.70.

y = 0.0015x1.7372 r 2 = 0.8867

y = 0.2342e0.0252x r 2 = 0.9154

0 20 40 60 80 100 **PGC (%)**

0 20 40 60 80 100 **PGC (%)**

reclassification method for Tobacco, Eggplant, Pepper and Soybean.

Pepper Soybean

Tobacco Eggplant

0

0

1

**LAI**

2

1

2

**LAI**

3

4

The productivity of a crop depends on the ability of plant cover to intercept the incident radiation, which is a function of the leaf area available, the architecture of vegetation cover and conversion efficiency of the energy captured by the plant in biomass.

Water stress and nutrition reduce LAI to a smaller size and greater leaf senescence. The smaller size of LAI agrees with light capture and thus crop growth, decreasing the efficiency of radiation.

The measurement of radiation intercepted by a crop for formation of leaf area is an important factor in monitoring crops, water relations studies, and nutrition and in crop simulation models

Measurements taken from digital images exhibit practical advantages with respect to the PAR bar, which must be used at solar noon. In contrast, measurements obtained with a digital camera can be taken at any time of the day and full sunshine is not necessary.

The data obtained by digital photography PGC allow rapid estimation of leaf area using a camera and free software obtaining LAI values in the simplest way than when measured with a planimeter carried out using destructive measurement and individual leaf analysis.
