Abstract
The experiment was conducted in a greenhouse during 2017 and 2018 growing seasons to evaluate the impact of the shading and various nutrition programs on mitigating heat stress, reducing the use of chemical minerals, improving the reproductive growth and yield of tomato plant. Split-plot within Randomized Complete Block Design (RCBD) with three replications was conducted in this study. Shading factor was allocated in the main plots and the nutrition programs distributed randomly in the subplots. Results indicate that shading resulted in the decrease of daytime temperature by 5.7˚C as an average for both seasons; thus a significant increasing was found in leaf contents of macro nutrients (Nitrogen, Phosphorous, and Potassium), and micro nutrients (Iron, Zinc and Boron), except the Iron content in 2018 growing season. Furthermore, shading improved significantly the reproductive growth and tomato yield. Among the plant nutrition programs, the integrated nutrient management (INM) including the application of organic substances, bio inoculum of AMF and 50% of the recommended dose of chemical fertilizers; lead to the enhancement of nutrients content, reproductive characteristics and plant yield. Generally, combination of both shading and INM showed positive effects on plants nutrient status and persisting balance on tomato flowering growth and fruits yield.
Highlights
Heat accumulation inside the greenhouses in late spring and summer seasons due to high and long duration of solar radiation leads to expose cultivated plants to heat stress
Several researchers confirm that heat stress reduces tomato yield through its effect on pollen viability, flower abortion, blossoms drop, fruit sets limit and the reduction in fruit weight [12, 21]
Many studies assured that greenhouses shading is very useful in reducing the negative effects of heat stress leading to the improvement of plants nutrient status, reproductive growth and plant yield [14, 17]
Summary
Heat accumulation inside the greenhouses in late spring and summer seasons due to high and long duration of solar radiation leads to expose cultivated plants to heat stress. Many studies assured that greenhouses shading is very useful in reducing the negative effects of heat stress leading to the improvement of plants nutrient status, reproductive growth and plant yield [14, 17]. Previous studies reported that a variety of biostimulant substances (i.e., humic and fulvic acids, hdrolysed proteins and amino acids containing products) and microbial inoculants (i.e., mycorrhizal fungi) have been introduced as efficient, safe, and sustainable tools to optimize root system, boosting crop performance, improving nutrient use efficiency as well as enhancing tolerance to heat stress [4, 5, 8]. The aims of this study were to examine the influence of shading and different nutrition programs including chemical, organic substances and bio fertilizers as a biostimulants, alone or in combinations on mitigating heat stress, reducing the use of inorganic fertilizers, improving reproducive growth and yield of tomato under uncontrolled greenhouse conditions. Results of some chemical and physical properties of the soil are shown in (Table 1)
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