Performance of Onion under Different Reduced Light Levels for Agroforestry and Intercropping Systems

Abstract

Performance of onion under different reduced light levels was evaluated at the Bangabandhu Sheikh Mujibur Rahman Agricultural University research farm during winter season, 1998-99. The light levels were 100, 75, 50, and 25% PAR (Photosynthetically Active Radiation). The reduced light treatments were imposed using mosquito nets immediately after the establishment of onion seedlings and were maintained up to final harvest. Except plant height, all the studied parameters of onion were decreased with the decrease of light levels. Plant height was increased with the increase of light levels where the tallest plant (61.87 cm) was observed under minimum light level, i.e. 25% PAR which was similar to 50% PAR level. The smallest plant (44.29 cm) was observed under full light (100% PAR). Number of leaves per plant and bulb diameter manifested an almost similar response where the highest values of both parameters were observed under full light level and did not vary significantly up to 50% light reduction. Further, significantly the lowest values were observed under 75% reduction of light i.e., minimum light treatment. Both fresh and dry yields of onion obtained under full sunlight were the highest (21.17 and 3.53 t/ha) but these yields were statistically equal to the yield obtained under 25% PAR reduction for fresh yield, and under 50% PAR reduction for dry yield, Compared with fresh and dry yields under full sunlight, the yield reduction under 25; 50; and 75% light reduction levels was 15 and 13; 28 and 20; and 42 and 41%, respectively.