Abstract
Water scarcity, due to physical shortage or inadequate access, is a major global challenge that severely affects agricultural productivity and sustainability. Deficit irrigation is a promising strategy to overcome water scarcity, particularly in arid and semiarid regions with limited freshwater resources. However, precise application of deficit irrigation requires a better understanding of the plant response to water/drought stress. In the current study, we investigated the potential impacts of biochar-based soil amendment and foliar potassium-humate application (separately or their combination) on the growth, productivity, and nutritional value of onion (Allium cepa L.) under deficient irrigation conditions in two separate field trials during the 2018/2019 and 2019/2020 seasons. Our findings showed that deficit irrigation negatively affected onion resilience to drought stress. However, these harmful effects were diminished after soil amendment using biochar, K-humate foliar application, or their combination. Briefly, integrated biochar and K-humate application increased onion growth, boosted the content of the photosynthetic pigments, enhanced the water relations, and increased the yield traits of deficient irrigation onion plants. Moreover, it improved the biochemical response, enhanced the activities of antioxidant enzymes, and enriched the nutrient value of deficiently irrigated onion plants. Collectively, these findings highlight the potential utilization of biochar and K-humate as sustainable eco-friendly strategies to improve onion resilience to deficit irrigation.
Highlights
Onion (Allium cepa L., Family: Amaryllidaceae) is a vegetable crop of high economic importance worldwide [1]
While deficient irrigation significantly reduced the plant height (Figure 1A; pirrigation < 0.0001) and total leaf area in both seasons compared with the regular irrigated onion plants, soil amendment using biochar, K-humate foliar application, or their combination significantly improved both plant height and total leaf area
Two field experiments were performed at the Elamaar village in the region of Sidi Salem (31◦07 N, 30◦57 E), Kafr El-sheik Governorate, Egypt, during two consecutive growing seasons (2018/2019 and 2019/2020) in order to determine the impact of soil application with biochar and foliar application of potassium humate (K-humate; Egyptian Company for Fertilizers and Chemicals, Attaka, Suez Governorate, Egypt) under deficient irrigation on growth, physiological traits, antioxidant activities, productivity, and the nutritional quality of onion plants in salt-affected soils
Summary
Onion (Allium cepa L., Family: Amaryllidaceae) is a vegetable crop of high economic importance worldwide [1]. It is a nutrient-dense vegetable, which is high in vitamins, minerals, and antioxidants while being low in calories. Under water stress, the onion reduces its photosynthesis, stomatal conductance, osmotic adjustment, evapotranspiration, and productivity [6,8]. Immense decreases in physiological processes (photosynthesis and stomatal conductance), bulb yield, and quality were attained owing to subjecting onions to water stress [6,7]. Once water shortage was imposed, leaf area and bulb growth significantly declined, with a decrease of 19–28% in onion yield [7]
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