The role of phosphorus fertilizers and planting techniques in mitigating drought stress in isabgol (Plantago ovata Forssk)

IntroductionPlantago ovata is classified in the Plantaginaceae family. Water and nutrients are crucial determinants of plant growth. Multiple studies indicate that the optimal effectiveness of fertilization occurs when plants are not experiencing water stress, while irrigation is most effective when nutrients are not limited. Drought stress is a complex form of stress that leads to alterations in the physiological, morphological, biochemical, and molecular characteristics of plants. Phosphorus is a vital nutrient necessary for the growth of plants. It facilitates plant maturation and promotes seed development. Intensive agriculture carries the potential for over-fertilization. Microorganisms play a crucial role in agriculture by facilitating the movement of plant nutrients and minimizing reliance on chemical fertilizers. Enhanced sowing techniques not only ensure the ideal number of plants by promoting better germination, but also allow for uniform and efficient utilization of land, light, and other input resources by the plants. Therefore, it is crucial to establish a planting arrangement that can prevent overcrowding and allow plants to optimize resource utilization with greater effectiveness and efficiency.Materials and methodsThe experiment was carried out as a split-factorial design with a randomized complete blocks arrangement. It was conducted at the research farm of Zabol University in Chah Nimeh, with three replications. The experimental treatments consisted of three levels of drought stress: irrigation after 60 mm (non-stress), 120 mm, and 180 mm evaporation from a class A evaporator (severe drought stress) as main factor. The sub-factor was the combination of seed planting method (flat or ridge planting) and phosphorus fertilizer types, which included 100% chemical phosphorus fertilizer, Phosphate Barvar2, and a combination of 50% chemical phosphorus fertilizer and Phosphate Barvar2. The following characteristics were analyzed: spike length, spike weight, spike density per square meter, grain yield per plant, individual plant dry weight, harvest index, grain protein content, mucilage percentage, seed husk percentage, and husk yield. The data analysis was conducted using SAS software version 9.1. To compare the means of treatments, Duncan's Multiple Range Test was employed with a significance level of 5%.Results and discussionThe findings indicated that the non-stress irrigation treatment combined with the application of phosphorus fertilizers resulted in the highest values for spike length, weight of spike, number of spike per m-2, grain yield per plant, single plant dry weight, and husk yield. The comparison results of the means of the interaction effects of irrigation and phosphorus fertilizers showed that the highest grain yield per plant (2.271 gr) was observed with the non-stress irrigation treatment and the combined use of phosphorus fertilizers. On the other hand, the lowest grain yield (0.741 gr) was associated with the treatment of severe drought stress and non-application of phosphorus fertilizers. Additionally, the highest seed protein (2.305 mg.g-1 seed weight) and mucilage percentage (15.04) were obtained from the irrigation treatment after severs drought stress with the combined application of phosphorus fertilizers. The husk percentage, was influenced by phosphorus fertilizers and planting methods with different irrigation levels. Applying phosphorus fertilizers and utilizing a ridge planting technique, along with irrigation triggered after 180 mm of evaporation from the evaporation pan, resulted in a 32% increase when compared to the standard irrigation treatment and absence of fertilizer.ConclusionThe utilization of phosphorus fertilizers resulted in a beneficial impact on both the quantity and quality attributes of grain yield per plant. The combined treatments had a more pronounced positive effect compared to applying phosphorus fertilizers individually. The primary factor contributing to the superiority of the flat planting method was the accelerated germination of seeds, which facilitated faster plant establishment. The research findings indicate that the most significant quantitative attributes of Plantago ovata were achieved through the irrigation treatment of 60 mm evaporation from the evaporation pan, coupled with the combined use of biological and chemical phosphorus fertilizers using the flat planting method.