The Effect of Moisture Depletion, Soil Conditioners, and Transpiration Inhibitors on the Physical Properties of Soil Cultivated with Sunflower (Helianthus annuus L.)

Abstract

      The experiment was conducted in the experimental field of the College of Agriculture, University of Wasit, located at a longitude of 45°50′33.5″ E and a latitude of 32°29′49.8″ N, during the 2023 autumn season. The study aimed to investigate the effect of moisture depletion, soil conditioners, and transpiration inhibitors on some physical properties of soil cultivated with sunflower (Helianthus annuus L.). The experiment was carried out using a split–split plot design (RCBD) with three factors.

The first factor was moisture depletion at two levels: 50% and 75% of available water. The second factor was soil conditioners, including two types, zeolite and perlite, along with a control without any amendment. The third factor was the transpiration inhibitor (Orslic) and a control without inhibitor. Sunflower seeds (Flamy variety) were sown on 1/8/2023 using the drilling method and harvested on 25/11/2023. All experimental units were irrigated twice before germination, based on the 50% moisture depletion level and the volumetric moisture content obtained from the soil moisture characteristic curve. Irrigation depths were calculated using soil moisture measurements and the water balance equation. Soil moisture content was determined after each irrigation and before the subsequent irrigation, according to the moisture depletion levels used in the experiment (50% and 75% of available water), to schedule irrigation throughout the growing season.

The main results can be summarized as follows:

1. The plots irrigated at 50% moisture depletion significantly outperformed those irrigated at 75% moisture depletion in reducing soil bulk density at the end of the season, with a value of 1.121 g·cm⁻³ compared to 1.176 g·cm⁻³ for the 75% treatment. Similarly, the 50% moisture depletion treatment significantly increased total porosity, reaching 55.493% compared to 54.089% for the 75% treatment. This treatment also exceeded the 75% treatment in saturated hydraulic conductivity, recording 1.14 and 1.09 cm/h, respectively. Additionally, soil aggregate stability was higher under the 50% moisture depletion treatment, at 27.2% compared to 25.9% for the 75% depletion level.
2. Treatments amended with zeolite significantly outperformed those with perlite and the control in reducing soil bulk density at the end of the season, with values of 1.093 g·cm⁻³ compared to 1.111 and 1.242 g·cm⁻³ for the perlite and control treatments, respectively. Zeolite also significantly increased total porosity (57.999%), saturated hydraulic conductivity (1.18 cm/h), and soil aggregate stability (28.1%) compared to perlite (55.98%, 1.15 cm/h, 26.6%) and the control (50.39%, 1.01 cm/h, 24.9%)