Abstract
Water scarcity imposes significant constraints on fruit production, especially in arid and semi-arid regions. Deficit water, as one of the policies used in enhancing water use efficiency, leads to growth reduction and adversely affects the quality of mango fruit yield. The current study aims to investigate the role of Azolla as a biofertilizer in mitigating the negative effects of water stress on mango (Mangifera indica L. cv. Eiwas). A field experiment consisting of 4 different treatments (2 irrigation regimes and 2 Azolla treatments) was conducted in a randomized complete block design with five replicates. Mango trees (12 years old) were irrigated at 80% of the available soil water (normal irrigation) or at 50% of the available soil water (deficit irrigation). Dried Azolla (0 or 5 t ha(-1)) was added to the soil. Mango tree growth and fruit yield were significantly reduced due to the deficit irrigation. In the first year, deficit irrigation reduced the available soil nitrogen (N), phosphorus (P), and potassium (K) by 35, 23, and 20%, respectively, and by 39, 21, and 18% in the second year. The addition of Azolla alleviated water stress and increased nutrient availability and uptake. The addition of Azolla to water-stressed mango plants increased N, P, and K uptake by 25, 25, and 22%, respectively, in the first year and by 33, 22, and 23%, respectively, in the second year. Keeping soil moisture at 50% of the available soil water had a negative impact on mango fruit quality characteristics. Water stress reduced the total soluble solids, total sugar, vitamin C, and pulp by 18, 16, 14, and 8%, respectively (average of 2 years). The addition of Azolla to mango plants under deficit irrigation increased water use efficiency (WUE) by 30 and 27% in the first and second years, respectively, while these increases were 14 and 33% under normal irrigation. The mechanisms employed by Azolla to lessen the detrimental effects of water stress on mango trees in this study include increased leaf area, protection of photosynthesis pigments, and increased secretion of substances that aid in water stress resistance, such as proline. The use of Azolla as a dry manure in arid-degraded soil reduces water stress on mango trees while increasing yield and fruit quality.