Optimising the rate and stages of application of nitrogen fertiliser for stevia under greenhouse conditions

Nitrogen (N) is the nutrient most used by crop producers and its application may affect the N use efficiency in crop production. The present study was conducted in order to determine the optimum N fertiliser rate and application stages (S) for stevia (Stevia rebaudiana Bertoni) production for the first cutting, under greenhouse conditions. A two-factorial experiment with four N fertiliser rates (0, 40, 80 and 120 kg ha−1 applied as urea) and three stages (sole split N applied at sowing; dual split N applied at sowing and one month after sowing; triple split N applied at sowing, one and two months from sowing) were laid out in a completely randomised design. Each treatment combination was replicated three times. The plants were grown in boxes (1 m−2, 40 cm high) filled with loam soil and the treatments were applied as described. Results showed that stevia growth and metabolites were significantly affected by N rates and application stages. Stevia leaf area index (LAI), leaf yield, leaf/stem ratio and harvest index (HI), steviol glycosides (SVglys) content, SVglys compositions and yield were the highest when 40 kg N ha−1 was applied in two stages. This was also true for leaf and SVglys yield. Splitting of N application of 120 kg ha−1 into three stages showed an inhibitory effect on some stevia traits such as SVglys content and yield. Based on the current results and efficient N application, 40 kg N ha−1 split into two stages is recommended for stevia production under greenhouse conditions.