Effect of doses fertilizer and harvest interval on the intensity of leaf spot diseases, production and quality of citronella grass (Cymbopogon nardus L.) essential oils in ultisols soil

Until now, Indonesia is still a world exporter of essential oils, including citronella oil. So that the role of farming communities in the development of Indonesia's essential oil industry is very helpful. For this reason, a study was carried out on response of fertilization and harvest interval on the intensity of leaf spot diseases of citronella grass, and productivity in ultisols soil which was carried out from October 2020 to September 2022. The experiment was arranged in a randomized block design in factorial with 9 treatments, as the first factor is 3 levels of an organic fertilizer (NPK); P1 = 25 g clumps ^-1, P2 = 37.5 g clumps ^-1 and P3 = 50 g clumps ^-1. The second factor is the harvest interval with three levels which is 4 = harvest interval once every 4 months, 3 = harvest interval every 3 months and 2 = harvest interval once every 2 months, repeated three times. Each treatment plot consisted of 24 clumps with a plant spacing of 1 × 1 × 1 m. Varieties used is Serai wangi 1. Parameters observed were intensity of leaf spot diseases, vegetative growth, livestock production, oil production, quality analysis and R/C ratio. The results showed that there was an effect of fertilizer doses and harvest intervals on the development of leaf spot disease. It was seen that at the application of fertilizer doses of 37.5 g clumps ^-1 with harvest intervals once every three months showed the lowest disease attacks, namely on Cuvularia sp and Pestalotia sp (5.98%, 5.42% and 7.98 %, 7.44 %). In addition, the development of vegetative growth is also influenced by the application of fertilizer doses and harvest intervals on the parameters of canopy width, plant height, leaf length, leaf width and number of tillers. The best fertilizer dose is 37.50 g clump ^-1 successively (175.40 cm, 172.29 cm, 113.62 cm, 2.36 cm and 119.59 stems), with harvest intervals every 3 months (179.40 cm, 187.29 cm, 119.44 cm, 2.45 cm and 120.00 stems), as well as fresh leaves production tons/ha/year and oil production kg/ha/year the best is the application of fertilizer doses of 37.50 g clumps^-1 with harvest intervals once every 3 months (67.81 tons^-ha-year and 578.61 kg^{-ha- year},with, 67.40 tons^-ha-th and 517.60 kg^-ha-th). For oil quality, numerically, the application of fertilizer at a dose of 37.50 g of clump ^-1 with harvest intervals every 3 months is still high. The proper R/C ratio for farming occurs in the 2 nd year by administering a fertilizer dose of 37.50 g clump^-1 and harvesting intervals once every 3 months with an increase of 116.67%. So, the citronella grass variety Serai wangi 1 can be developed on ultisol soil types by applying an organic fertilizer (NPK).