Effect of Foliar Humic Acid on Water Productivity: Biochemical Parameters and Biotic Stress on Geranium Yield

During the 2017/2018 and 2018/2019 seasons, a study was conducted on the effect of humic acid at 1.0, 1.5, and 2.0 ml L-1 and water productivity on essential oils and proline content, biotic stress caused by Cucumber Mosaic Virus (CMV) and yield of geranium plants. The study was conducted in El Kanater El Khairia of Qalubia Governorate. It was aimed at determining the appropriate concentration of humic acid that attains the highest water productivity (WP), the highest production of essential oils, and highest proline content as well as reducing the symptoms of CMV. Results indicate that the highest fresh yield was obtained with a foliar application of 2.0 ml L-1 humic acid and 120% evapotranspiration (ETo). Applied irrigation water was 15155, 12168, and 9334 m3 ha-1 in the first growing season and 15218, 12298, and 9678 m3 ha-1 in the second growing season with 120, 100, and 80% ETo in both seasons. The highest average of WP 9.31 kg ha-1 both seasons was attained with 80% ETo and, 2.0 ml L-1 humic acid. While, the highest percentage of geranium essential oils and proline content, 68.16 and 3.73%, respectively were found with 2.0 ml L-1 humic. On the contrary, there was a significant reduction in CMV symptoms in plants treated with 2.0 ml L-1 humic acid compared to untreated controls. Thus, it is recommended that geraniums be irrigated with 80% ETo and application of 2.0 ml L-1 humic acid. Additionally, these treatments increased WP and resulted in the highest production of essential oils. It also increased the concentration of proline which acts as an endogenous osmoprotectants, against CMV.