Folia Horticulturae

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Solar spectral irradiance in cultivated plants under cover in a submontane region. II. Tomato plants in the greenhouse

Marian Czarnowski*, Stanisław Cebula**

**The Franciszek Górski Department of Plant Physiology
**Polish Academy of Sciences
**Sławkowska 17, 31-016 Kraków, Poland
**Department of Vegetable Crops
**Faculty of Horticulture, Agricultural University
**29 Listopada 54, 31-425 Kraków, Poland

Spectral quantum irradiance in the midday hours on a sunny day in April, measured above the greenhouse tomato plants in a submontane region, reached a maximum value of 4.8 μmol m-2 s-1 nm-1 at a wavelength of 670 nm. The quantum irradiance (300-1100) amounted to 2620 μmol m-2 s-1. The photosynthetically active radiation (400-700 nm, PAR) above the cultivated tomato plants at that time attained a value of 1210 μmol m-2 s-1.

The transmittance of solar radiation through the tomato plant canopy depends on the value of the leaf area index (LAI). The lowest PAR transmittance through the canopy was 1-6% (at LAI=2.3-3.2) of the PAR value above the culture. This demonstrated high PAR absorptance by the tomato plants. A single leaf revealed high absorptance (78-90%), low reflectance (6-8%), and slightly higher transmittance (7-12%) in the PAR range, while in the near infrared (over 700 nm), the leaves revealed very low absorptance (5-7%), but considerable reflectance (about 47%) and transmittance (about 47%). High absorptance of solar energy in the PAR range, and high reflectance and transmittance of irradiation in the near infrared have a significant effect on the photosynthetic production of plants.

Czarnowski M., Cebula S., 1994. Solar spectral irradiance in cultivated plants under cover in a submontane region. II. Tomato plants in the greenhouse. Folia Horticulturae VI/2: 15-23.