INFLUENCE OF SOME AGRICULTURE TREATMENTS ON GROWTH AND PRODUCTIVITY OF STEVIA (STEVIA REBAUDIANA BERTONI) UNDER DESERT LANDS CONDITIONS

ABSTARCT
A field experiment was conducted in the Northwestern desert of Egypt in the Siwa Oasis region during the 2020/2021 and 2021/2022 seasons to elucidate the influence of plant spacing D1 (50×15 cm), D2 (50×30 cm), and D3 (50×54 cm) combined with biofertilization treatments (Bacillus megatherium (B), Azotobacter chroococcum (A), Mycorrhiza sp. (M), and the mixture between them) on growth and productivity of stevia plant as well as soil microbiological properties.
 The results verified that, concerning the effect of interaction, the lowest planting density D3 (50x45 cm = 18600 plants/feddan) with a mix of biostrains (Mycorrhiza, Bacillus, and Azotobacter) recorded a significant increase in plant height, herb fresh and dry weights per plant, total chlorophyll, plant NPK content, soil total microbial count, Azotobacter, Bacillus, and Mycorrhiza counts. While the highest fresh and dry yield per feddan were obtained from the interaction treatment between D1 and the mixture of biostrains. Moreover, the highest soil phosphatase and dehydrogenase activity were noticed from the interaction treatment between D3 and mixture of the three strains. In contrast, the interaction treatment between D2 (28000 plants/feddan) and mix biostrains gave the highest nitrogenase activity and the highest value of stevioside content. While the greatest plant spacing (D3) combined with the mix biostrains (A, B, and M) recorded the highest value in rebaudioside content in the stevia plants.