Reduction of Nitrate Content in Response to Salicylic Acid in Spinach and Parsley Fertilized with Two Different N-Sources

Abstract

Spinach and parsley are hyper-nitrate accumulator vegetables, thereby constituting a possible human health risk. For that, pot and two field experiments were conducted to investigate the effect of exogenous salicylic acid (SA) application on yield, nitrate content and another quality parameters in spinach and parsley using two different ammonium fertilizers as ammonium sulfate (A. sulfate) and urea. The results of pot experiment (factorial, 2 x 2) showed that, A. sulfate-fertilized plants produced maximum yield compared to urea-fertilized ones, which companied with high level of nitrate content (up to 942.6 and 604.5 mg Kg -1 FW in spinach and parsley, respectively). Application of 5 µM of SA reduced nitrate content by about 18 and 10 % in A. sulfate-fertilized plants and by 50 and 7 % in ureafertilized plants, in both spinach and parsley, respectively. Under field conditions, using only urea fertilizer, nitrate was decreased to minimum levels, 679.0 and 395.6 mg kg -1 FW, in spinach and parsley, sprayed with 20 and 5 µM-SA, respectively. This reduction was associated with induction of nitrate reductase (NRase) activity. The maximum percentage of NRase activity over control (74%) was recorded in spinach treated with 20 µM of SA and reached to 60 % in parsley treated with 5 µM-SA. Also, spraying of SA increased marketable yield, vitamin C and total free amino acids contents in both tested leafy vegetables. It was concluded that, SA application preserved nitrate content in safe limit for human consumption.