GROWTH, YIELD COMPONENTS AND CHEMICAL CONSTITUENTS OF Stevia rebaudiana Bert. AS AFFECTED BY HUMIC ACID AND NPK FERTILIZATION RATES

Abstract

Two field experiments were carried out during 2016 and 2017 consecutive seasons ata Private Farm at Mit-Ghamr Distrect, Dakahlia Governorate, Egypt, to study the effect of humic acidrates (0.0, 325.60, 651.2 and 976.80 g/fad.), NPK fertilization rates [0.0, 25, 50, 75 and 100% of therecommended rate (RR)] and their interactions on growth, leaves and herb yield and some chemicalconstituents as well as active ingredients of stevia plants. The obtained results referred that themaximum value for each of plant height, branch and leaf number/plant, total dry weight/plant, dryweight of leaves and herb/fad., total N, P, K and total sugar percentages as well as total chlorophyllcontent (a+b) were detected when plants were applied with the highest rate of humic acid (976.80g/fad.) and fertilized with 75% RR of NPK, in most cases. The main constituents of Stevia rebaudianaleaves as detected by high performance liquid chromatography-mass spectrometry (LC-MS) wereRebaudioside A, Rebaudioside B, Rebaudioside C, Dulcoside and Steviolbioside which increased withtreatment of 100% RR of NPK fertilizers combined with the highest rate of humic acid (976.80 g/fad.)compared to control.