Impact of Shading on Tomato Yield and Quality Cultivated with Different N Doses Under High Temperature Climate

Abstract

Temperature increase is among the most important issues associated with climate change. Several studies have shown that the production and quality of vegetable crops can be directly or indirectly affected by high temperature. There are different techniques used to mitigate the adverse effects of heat stress as the use of sun shade-cloths inside the greenhouse. Under these conditions, plant response to mineral nutrition can be altered and therefore, studies on the interaction between shading and mineral management are needed in order to optimize crop productivity and quality, avoiding excessive application of fertilizers that could lead to undesirable consequences such as environmental contamination. This study examines the interaction between the effect of shading and increased N doses over the production and nutritional quality in tomato grown under high temperature conditions (maximum day temperatures up 45°C during the fruiting period). Plants were grown under greenhouse conditions in 20L-pots, and irrigated with nutrient solution containing 3, 7 and 14mM N. These treatments were combined with two different shading treaments: non-shaded (control) and shaded plants covered with AOL S40 shadecloth that attenuated approximately 50% of the direct sunlight and reduced temperature about 11°C during the day time. Under non-shade conditions, decreasing N dose produced a decrease of the total fruit yield. However, under shade conditions, the highest total yield was obtained in plants cultivated with 7mM N. In addition, the highest value of mean fruit weight among all the shading and N treatments was obtained under shading + 7mM N treatment. Regards fruit quality, the use of shadecloth led to an increase in fruit lycopene concentration regardless of the N treatment. The results show that N doses should be adjusted when using shading for reducing air temperature in warm climate zones, in order to avoid excessive fertilization.