Effects of rate and application frequency of nitrogen fertiliser on biomass yield and sweetness quality of stevia (Stevia rebaudiana Bertoni)

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A.G. Rosnani, R.A Halim, M.K. Yusop and M.A. Mohd Shukri

Abstract
Human life styles have changed so much and awareness on the use of sugar or sweeteners has become an integral part in our daily diet. Sweeteners which are high in calorie like white sugar, brown sugar, corn syrup, maple syrup, molasses and fruit syrups found in natural and processed are hazardous to our health. Stevia is very popular and ideal to substitute sugarcane. A study was conducted to determine optimum nitrogen (N) level and fertiliser application frequency (A) for high biomass yield and sweetness quality (content, yield, ratio) of stevia. A total of seven different levels of N and two application frequencies (after every harvest, A1 and after every two harvest, A2) were tested. Results indicated that biomass yield escalated with increased level of N up to 250 kg N/ha. At this level, total dry matter yield from four times of the harvesting frequency was 6 t/ha. There were interaction between N and A on glycoside content and glycoside yield of stevia. The maximum stevioside (St) content was about 85 mg/g at A2, under control treatment (0 N). Meanwhile, the maximum rebaudioside-A (Reb-A) content was 25 mg/g, better at A1 when plant treated with 40 kg N/ha as compared with A2. The St and Reb-A yield were better with application of 210 kg N/ha and 170 kg N/ha, respectively, at A2. Sweetness index of stevia was calculated by ratio of Reb-A to St because Reb-A possess the sweetest compound in stevia. It was found that application of N fertiliser at 50 kg/ha and at A1, the sweetness of stevia was high with the ratio of Reb-A to the St of 0.4.

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