Ammonium to Total Nitrogen Ratio Interactive Effects with Salinity Application on Solanum lycopersicum Growth, Physiology, and Fruit Storage in a Closed Hydroponic System

Nikolaos Tzortzakis,Aristeidis Stamatakis,Antonios Chrysargyris,Georgia Pitsikoulaki

doi:10.3390/agronomy12020386

Abstract

Using high-salinity water for plant fertigation may have negative consequences for plant growth, overall yield and crop quality. In the present study, the effects of NaCl-salinity in conjunction with three different ammonium to nitrate ratios (Nr) on tomato (Solanum lycopersicum Mill.) plant growth, nutritional status, yield, fruit quality and postharvest storage were examined. The electrical conductivity (EC) was increased by adding NaCl into the nutrient solution and three different Nr ratios were applied, Nr0.05, Nr0.10 and Nr0.15, while the other macronutrient and micronutrient concentrations were constant in all treatments. The EC of the nutrient solution supplied to the plants was 2.2 mS cm−1 at the low salinity treatments and 7.5 mS cm−1 at the high salinity treatments. Increased salinity resulted in decreased plant growth factors and fruit yield, despite the Nr. An increased Nr reduced the pH value of the nutrient solution, while the fruits of the plants cultivated under high salinity obtained reduced Ca, K, Mg, P and N content. Reduced Ca content can lead to blossom end rot disorder and this was evidenced on tomato cultivation under high salinity. However, in the present study, this disorder appeared at the very late stages and did not affect the marketability of the fruits. On the other hand, both salinity and Nr0.15 increased fruit firmness at harvest or following storage, while citric acid, total soluble solid and vitamin C contents were also increased by salinity. Total phenols were increased by salinity at harvest, and lycopene and β-carotene content were increased by salinity at harvest and/or following storage at 12 °C or 25 °C. Salinity enhances fruit quality and improves the organoleptic characteristics of the crop, while an appropriate Nr ratio may restrict the detrimental effects of salinity on the nutritional status of plants by regulating the pH in hydroponic systems.

Highlights

Introduction iationsSalinity and a lack of high-quality irrigation water are two key side effects of ongoing climate change that have a negative impact on plant physiological processes, plant growth and agronomic performance, with serious implications for global horticulture crop output [1,2]
This study explored the effects of salinity on hydroponically grown tomato plants and evaluated whether the application of different nitrate ratios (Nr) levels affected the negative effects posed by NaCl stress
Salinity and high ammonium ratios induced nutrient imbalances in the fruit, such as Ca, and affected blossom-end rot” (BER) in fruits, the symptoms of which appeared on the fruits above the third cluster after five months of tomato cultivation (March) and did not affect the marketability of the examined fruits

Summary

Introduction

Salinity and a lack of high-quality irrigation water are two key side effects of ongoing climate change that have a negative impact on plant physiological processes, plant growth and agronomic performance, with serious implications for global horticulture crop output [1,2]. Salinity stress has been shown to have a deleterious impact on plant physiological and biochemical processes, affecting both the primary and secondary metabolism of plants [6]. Increasing sodium chloride (NaCl) levels has been demonstrated to have a negative effect on plant height and vigor [7,8,9], leaf area [10,11] and leaf number [12,13].

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Discussion

Conclusion