Comparison of Antioxidant Activity and Antioxidant Components in Lettuce,Onion and Tomato Obtained with Different Levels and Forms of Nitrogen Fertilization

The effect of N levels and sources on the antioxidant components in vegetable is not completely understood. Therefore, greenhouse experiments were conducted to determine the changes in antioxidant capacity diphenyl-2-picrylhydrazyl （DPPH） and ferric reducing antioxidant power （FRAP）, total phenolics, ascorbic acid, total carotene and lycopene contents in edible portions of lettuce, onion and tomato due to different nitrogen levels and sources. The experiment included three N levels （20, 40 and 60 kg/ha for lettuce trial and 60, 120 and 180 kg/ha for either onion or tomato） and four nitrogen sources （calcium nitrate, ammonium sulphate, ammonium nitrate and urea）. The antioxidant capacity and phenolic contents in lettuce was enhanced under low nitrogen level, while the antioxidant capacities, phenolics, carotenoids and lycopene in tomato fruits were not significantly affected by the nitrogen dose applied. Application of calcium nitrate caused 50% increase in DPPH and 20% in FRAP of lettuce compared to other nitrogen forms. Tomato treated with calcium nitrate or ammonium sulphate had higher phenolic and ascorbic acid contents than treated plants with ammonium nitrate or urea. Antioxidant tested parameters of onion were not significantly affected by the nitrogen treatments. Nitrogen concentration in tomato fruits significantly correlated with FRAP antioxidant capacity, phenolics, ascorbic acid, carotene and lycopene contents.     

The Applicability of the Local and International Water Quality Guidelines to Al-Gassim Region of Central Saudi Arabia

The quality of 109 water samples, comprised of 70 drinking waterand 39 irrigation water samples, in Al-Gassim Region of SaudiArabia was investigated with respect to total dissolved salts(TDS), electric conductivity (EC), pH, total hardness and themajor cations (Ca²⁺, Mg²⁺, Na⁺ and K⁺) andanions (Cl^-, SO₄ ^2-, NO₃ ^-,F^- andHCO₃ ^-) beside coliform bacteria as an indicator offaecal contamination.The concentrations of TDS varied widely, from 109 to 6995 mgL^-1, with a mean of 1427 mg L^-1. Of the 109 watersamples examined, 81 (74.3%) comply with the maximumpermissible drinking water limits set by the local and international standards and guidelines and 28 (25.7%) were abovethe limits of these standards. The concentrations of the cationsand anions (with the exception of NO₃ ^- and F^-)follow, more or less, a trend similar to TDS. NO₃ ^- concentrations (range 0–30 mg L^-1) comply with the limitof 50 mg L^-1 NO₃ ^- as the highest tolerableNO₃ ^- content. The concentrations of F^- indrinking water (range 0.2–1.5 mg L^-1) are alarming since88% of samples were below the lower permissible limit of 0.6 mgL^-1 set by SASO (1984), the guideline of the WHO is 1.5 mgL^-1 while the EEC maximum concentration lies within the range 0.7–1.5 mg L^-1. Microbiological analyses showednegative coliform tests, which confirms that they are devoid ofany faecal contamination.