Nitrogen metabolism of Aloe vera under long-term diluted seawater irrigation

Abstract: Diluted seawater such as 10% (10 volumes of seawater and 90 volumes of freshwater), 25%, 50%, 75% and 100% were used to irrigate Aloe vera L. during four successive years in Ledong region, Hainan Province of China. The effect of seawater irrigation on nitrogen metabolism of aloe plant was studied. Total nitrogen content of aloe leaves ranged from 1.48 to 1.56 % of dry matter, and no significant differences were observed between control (freshwater irrigation) and seawater treatments. The total nitrogen content of aloe roots, in the range of 0.74 to 0.85 % of dry matter, was much lower than that in the leaves. There was no significant difference in total nitrogen content of roots between control and seawater treatments. It is suggested that seawater treatments do not affect nitrogen uptake and transport in aloe plant. The nitrate content in aloe leaves irrigated with seawater was much lower than that with fresh water irrigation, and a continuous decline in nitrate content was noted with increasing seawater concentration. The nitrate/total nitrogen ratio also tends to decrease in leaves suggesting that nitrate has been assimilated into osmoregulated substances under seawater stress. The amino acid content of aloe plant was not affected, while the ratios of amino acid/total nitrogen significantly increased under seawater stress as compared with control. The protein content and protein/total nitrogen ratios were not affected by seawater treatment except for 100%, suggesting that there was a favourable transformation from amino acids to proteins under salt stress. It is concluded that a long term irrigation by diluted seawater on leachable sandy soil with excessive annual rain precipitation could effectively maintain yield and improve the quality of aloe.