The effects of silicon added to the nutrient solution either at a standard electrical conductivity (EC) of 2.2 dS m-1 or at an increased EC of 4.8 dS m-1 on yield, nutritional status and fruit quality were investigated in a tomato crop grown in a closed hydroponic system. Si was added in form of a water-soluble potassium silicate compound at a reference concentration of 2.25 mM. The EC was raised either by NaCl or by extra addition of K, Ca, and Mg salts of nitrates and sulfates at rates resulting in the same K:Ca:Mg and NO 3 :SO 4 ratios and NH 4 , P, and micronutrient concentrations in all treatments. The average EC values in the drainage water were 3.7 and 3.4 dS m-1 in the low EC treatments without and with Si supply, respectively, and 5.8, 5.7 and 5.8 dS m-1 in the salinity treatments involving NaCl addition, NaCl and Si addition, and extra nutrients combined with Si addition, respectively. The increase of the EC up to 4.8 dS m-1 by adding NaCl had no significant influence on the fruit yield of tomato, when Si was added to the saline nutrient solution. In contrast, the fruit yield per plant was significantly restricted at this level of salinity, when no Si was added to the NaCl-enriched nutrient solution, or when Si was included but salinity was induced by extra addition of major nutrients. In both cases, the yield depressions were exclusively due to a lower mean fruit weight. The β-carotene and lycopene contents of fruit were significantly increased by Si and nutrient-induced salinity. Both Si and EC enhanced the fruit firmness and the contents of total solid solutes and vitamin C in the tomato fruit. Moreover, the addition of Si significantly restricted the occurrence of blossom-end rot in tomato fruit when the plants were not exposed to salinity.

BACKGROUND Using water with high salinity for plant fertigation may have detrimental effects on plant development and total yield and on the quality of the crop produced. As a possible means to alleviate the negative effects of salinity, silicon (Si) can be incorporated in the nutrient solution supplied to plants. In the present study, hydroponically grown tomato (Solanum lycopersicum Mill.) plants were subjected to two different salinity levels (0 and 50 mmol L−1 NaCl) with and without the application of Si (0 and 2 mmol L−1 K2SiO3) in order to evaluate its possible positive impact on mitigation of salinity stress‐induced symptoms. An additional experiment was implemented with postharvest Si application (sodium silicate) to investigate effects on the shelf‐life of tomato fruit. RESULTS Salinity (50 mmol L−1 NaCl) decreased plant size, total yield and fresh fruit weight while a high percentage of blossom end rot symptoms of tomato fruit was also observed. The application of Si in the nutrient solution counteracted these detrimental effects, generating a higher yield and healthier fruit (lower blossom end rot incidence) compared to the untreated plants (no application of Si). Salinity improved several quality‐related traits in tomato fruit, resulting in higher marketability, whereas the addition of Si (pre‐ and postharvest) maintained fruit firmness following storage thereby increasing the shelf‐life of tomato fruit. CONCLUSIONS These findings indicate that Si application (pre‐ and postharvest) could provide an effective means of alleviating the unfavorable effects of using low‐quality water in plant fertigation on tomato plant development, fruit yield and post‐harvest quality, through increased fruit firmness. © 2019 Society of Chemical Industry

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Soil proteomics, the large-scale characterization of the entire protein complement in soils, provides a promising approach for deciphering the role of microbial functioning in terrestrial ecosystems. However, the extraction of soil proteins in sufficient quantities and of adequate purity remains a challenging task mainly due to the co-extraction of interfering humic substances. Up to now, the treatment of soil extracts with liquid phenol has been the "gold standard" for reducing humics, while the NoviPure cleanup kit was recently launched as a non-toxic approach. The present study describes an alternative method for delivering high-purity proteins based on humic coagulation with trivalent aluminum ions (Al). Various experimental parameters were optimized individually in order to maximize protein yield and diminish co-extracted humics. The optimized method was applied on a set of soil samples with diverse physicochemical characteristics and a comparison with the other two techniques was conducted. The amount of residual humics resulting from Al-based method was 26 and 35% higher than that from phenol treatment and NoviPure Kit, respectively, but these differences were of marginal statistical significance. With regard to extracted proteins, the average yields of the three methods were comparable, without showing any statistically significant differences. Overall, humic coagulation with Al offers comparable cleanup performance in terms of protein yield and purity, but it is less toxic and less complex than the phenol-partitioning method, whereas it is far less expensive than the NoviPure Kit. The new technique is expected to facilitate the implementation of proteomic studies in soils.

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