Effect of shading on tomato plants grow under greenhouse

Abstract

The experiment was conducted at Universidade Federal de Santa Maria, Rio Grande do Sul State, Brazil, to determine the effect of shading on tomato plants grown in a greenhouse. Sowing was done on July 4th and planting on August 27th, 2000, in a plant density of 3.3 plants m-2, using an organic commercial rooting medium. Water and nutrients were supplied on a daily basis using a nutrient solution. Two polyethylene tunnels (2.20 m height, 5 m width, 15 m length) were used. In the first plastic tunnel, used as control, the transmissivity of global radiation was 83% and plants were conducted as a commercial crop. In the second tunnel, plants were grown under a 52% shading screen. Plant growth and development were measured at 19; 26; 33; 40; 47; 54; 61; 75 and 89 days after beginning of anthesis. Daily average solar radiation in the first tunnel from planting time to the end of the experiment was 12.4 MJ m-2 day-1, whereas in the shaded tunnel it was 5.0 MJ m-2 day-1. Number of fruits per square meter did not differ significantly between the unshaded control and shaded tomato plants. At the last harvest, dry mass from unshaded and shaded plants differed significantly, with values of 974.9 g m-2 and 762.5 g m-2 for total dry mass, 550.1 g m-2 and 419.74 g m-2 for fruits, and 424.75 g m-2 and 342.74 g m-2 for vegetative organs, respectively. Total plant growth was reduced to 21.7% by shading, but plants continued to grow, in spite of the radiation level below the trophic limit of 8.4 MJ m-2 day-1. To establish the climatic suitability of horticultural crops in different regions, it should be advisable to take in account other variables than solar radiation.