Effect of Humic Acid Application And Soil Moisture Depletion Levels on Water Consumption and Water Use Efficiency of Potato (Solanum Tuberosum L.) Under a Drip Irrigation System

Abstract

A field experiment was conducted during the spring growing season of 2025 at the First Agricultural Research Station (Al-Bu'aitha), College of Agriculture, University of Anbar, located in Ramadi District, Anbar Province, Iraq (43°10′48″ E, 33°26′40″ N). The experiment was carried out on a sandy clay loam soil classified as Typic Torrifluvents. The study aimed to evaluate the effect of humic acid application levels and soil moisture depletion percentages on crop water consumption and water use efficiency of potato (Solanum tuberosum L.) under a drip irrigation system. The experimental treatments consisted of three humic acid levels: no application (A0), application of 37 mg organic carbon kg⁻¹ soil (A1), and application of 75 mg organic carbon kg⁻¹ soil (A2), combined with three soil moisture depletion levels (20%, 40%, and 60%) of available water. The results showed that the seasonal crop water consumption at the 20% depletion level reached 300.88, 278.14, and 272.52 mm season⁻¹ for A0, A1, and A2, respectively. Thus, humic acid application achieved water savings of 22.74 mm and 28.36 mm under A1 and A2, respectively, compared with the control treatment. At the 40% depletion level, water consumption values were 301.82, 277.09, and 262.15 mm season⁻¹, corresponding to water savings of 24.73 and 39.67 mm under A1 and A2, respectively. At the 60% depletion level, the corresponding values were 301.18, 283.53, and 263.43 mm season⁻¹, resulting in water savings of 17.65 and 37.75 mm under A1 and A2, respectively. The results also indicated a significant improvement in total tuber yield, which reached 42.58 Mg ha⁻¹ under A2 compared with 37.56 Mg ha⁻¹ in the control treatment. Moreover, water use efficiency increased to 0.160 Mg mm⁻¹ season⁻¹ under A2 compared with 0.124 Mg mm⁻¹ season⁻¹ under A0. The highest water use efficiency was recorded under the interaction treatment (D1A2), reaching 0.176 Mg mm⁻¹ season⁻¹.