Title : Improving drought tolerance of vetiver grass (Chrysopogon zizanioides l. roberty) by vermicompost and water-superabsorbent polymer application
Abstract:
Global warming, a critical aspect of climate change, is raising the Earth’s average temperature and altering rainfall distribution, leading to more frequent drought episodes. Drought stress is a severe abiotic factor that adversely affects plant survival, establishment, and productivity by reducing water availability. Under drought conditions, water lost through transpiration exceeds the amount absorbed, leading to a decline in plant water potential. This reduction disrupts essential cellular activities such as cell division, organ growth, and nutrient uptake, impairing stomatal function and photosynthesis, and ultimately diminishing plant biomass and productivity. To counter these effects, soil amendments such as vermicompost and superabsorbent polymers (SAPs) have been employed to enhance water retention and nutrient availability, thereby improving plant resilience. In this study, 135 two-year-old vetiver grass (Chrysopogon zizanioides L. Roberty) scions were collected and planted in 5-kg pots in the Malayer University greenhouse under controlled conditions (15–28°C, 14-hour photoperiod) for 120 days. The experimental soil, a sandy loam derived from the top 10 cm of field soil, was amended with vermicompost produced from cow manure and Eisenia fetida earthworms and mixed with a superabsorbent polymer (A200 SAP) at a depth of approximately 10 cm. The experiment consisted of ten treatments arranged in a completely randomized design with five replicates, ranging from a control (soil irrigated to field capacity) to various drought stress conditions (25% field capacity) with different concentrations of vermicompost (20% and 40% v/v) and SAP (4 and 6 g kg?¹), used individually or in combination. At harvest, assessments were made for biomass production (both aboveground and underground), survival capacity, and leaf area. Additionally, biochemical analyses quantified soluble sugars, essential oil content, hydrogen peroxide, proline, electrolyte leakage, malondialdehyde (MDA), and glycine betaine. Results showed that drought stress significantly reduced aboveground biomass, with the lowest value of 17 g recorded in the control. In contrast, treatments incorporating vermicompost and SAP markedly increased shoot biomass—achieving up to 50 g in the highest amendment treatment (D + V2 + SAP2). Underground biomass increased under drought stress, and higher levels of soil amendments further enhanced root development. Survival capacity and leaf area were severely diminished by drought; however, these attributes improved significantly with the application of vermicompost and SAP, particularly at elevated amendment levels. In drought-stressed plants, soluble sugars and essential oil contents increased, peaking at 28.4 mg g?¹ FW for sugars and 0.93% for oil in the D + V2 + SAP2 treatment. Moreover, stress markers including hydrogen peroxide, proline, electrolyte leakage, and MDA were elevated under drought conditions but were substantially reduced by vermicompost and SAP, indicating improved oxidative balance and membrane stability. Glycine betaine content also increased under water deficit and was further enhanced with higher amendment levels. These findings demonstrate that the combined application of vermicompost and SAP effectively mitigates drought stress in vetiver grass by improving water retention, nutrient absorption, and overall physiological performance. The enhanced biochemical responses and growth under water deficit conditions underscore the potential of these amendments to support sustainable cultivation of this valuable species in arid and semi-arid regions.
