Effect of nickel addition on the yield and quality of parsley leaves

Parsley (Petroselinum crispum) plants of the flat-leaf type (var. neapolitanum) were grown in plastic pots filled with Nile-delta clay soil. One-month-old plants were soil supplemented with 0, 25, 50, or 100 mg Ni per kg soil using NiSO4 solution of different concentrations. Parsley leaves were first harvested 2 months after seed sowing and reharvested again for 3 additional harvests at monthly intervals. At each harvest, leaf fresh and dry weights, number per plant, area. and chlorophyll content were measured. Dried leaves were then analyzed for N, P, K, Ca, Mg, Fe, Mn, Zn, Cu, and Ni contents. Total soluble solids (TSS), titratable acidity, L-ascorbic acid (LAA), nitrate, and ammonium contents were measured in the fresh leaves of the first two harvests, while those of the second two harvests were used for essential oil extraction which was analyzed for the essential constituents. Low levels of Ni fertilization, particularly 50 mg/kg soil, increased parsley leaf yield and quality without affecting leaf chlorophyll and Fe contents, but reduced TSS, LAA, nitrate, and ammonium levels. Increasing Ni levels up to 100 mg/kg soil resulted in visible symptoms of leaf chlorosis which coincided with a sudden drop in leaf chlorophyll content and reduced N, and Mg levels relative to that of the control. The main aroma constituent of parsley leaves, 1,3,8-p-menthatriene, which forms about 62% of the essential oil. showed a 10-25% increase over that of control with 25 mg or higher levels of Ni fertilization per kg soil. It is suggested that low levels of Ni fertilization, particularly 50 mg/kg clay soil. strongly improve not only parsley leaf yield and quality (i.e., leaf area, mineral content, oil yield, and flavor) but also the leaves are safer for human consumption since their nitrate and ammonium contents are significantly reduced. (C) 1999 Elsevier Science B.V. All rights reserved.