The Role of Selected Treatments in the Parameters of Leaf Growth and Yield of Stevia Plants Under Deficit Irrigation System

Abstract

A field experiment was conducted at Research Station A, which is one of the research stations affiliated with the College of Agricultural Engineering Sciences - University of Baghdad (Al-Jadriya), at a cloth house (Saran) and a shading rate of 25%. The study aimed to increase the plant yield, whether foliar or of the active compounds, and link water consumption with the presence or absence of the leaf area (plant cutting). The experiment was carried out using the randomized complete block design (RCBD) according to the split-plot design arrangement with three replicates. Each main experimental unit contained 5 rows (representing secondary units), where the distance between one row and another was 75 cm, and between plants 20 cm. Then, a separation distance was left between the main experimental units of 1.5 m. The main plots represented the irrigation factor (I1 full irrigation treatment, I2 deficit irrigation treatment with an amount of 50% of the amount of water added to the comparison treatment for two irrigations immediately after cutting. Besides, I3 deficit irrigation for three irrigations immediately after cutting). Conversely, the sub-plots were represents all treatments that treated after 30 days of cutting, which is the comparison and spraying of kinetin with a concentration of 10 mg.L-1. Plus, spraying the growth retardant Cycocel (CCC) with a concentration of 100 mg.L-1, pinching and spraying Licorice extract with a concentration of 5 mg.L-1. The experiment results showed a significant decrease in the number of branches, leaf area, and leaves dry weight with each increase in the irrigation level of the first and second cuttings. However, the number of leaves and the content of chlorophyll decreased with each increase in the irrigation level of the first cutting, and the relative water content decreased with each increase in the irrigation level of the second cutting. All treatments were superior to the comparison treatment in the number of branches and the yield of dry leaves in the first and second cuttings. The treatments of pinching and Cycocel were significantly superior to the two comparison treatments and Licorice in the number of leaves per plant in the first cutting, and the treatments of kinetin and Licorice were superior to all treatments in the leaf area in the second cutting. Also, the treatments of Licorice, kinetin, and cycocel were significantly superior to the comparison and pinching treatments in the relative water content in the second cutting. Though the treatment of kinetin was significantly superior to all treatments in the content of chlorophyll A in the first and second cutting, and the treatment of kinetin was significantly superior to the comparison, cycocel and pinching treatments in the content of chlorophyll b in the first cutting.