Autotrophic Nitrification in Soils Irrigated with Diluted Seawater

Abstract

Application of seawater diluted to 10, 20 or 40% concentration in deionized water was found to exert no significant effect on soil pH. The electrical conductivity of these soils was found to increase in value to attain levels of 3.15, 4.87, and 8.00 mmhos/cm at 25 C after 6 hours of incubation respectively. Incorporation of neither concentration however exerted no deleterious effect on heterotrophic growth in soil. Counts of about 10 million cells/g were therefore obtained after 14 days of incubation.
Growth of Nitrosomonas was stimulated by seawater application at 10% concentration. Whence, counts of 1.6 x 105 cells/g were observed after 28 days of incubation. Conversely, a ten-fold growth suppression over the control treatment was noted for this bacterium in soil treated with 20% seawater. Incorporation of 40% seawater had virtually prevented Nitrosomonas propagation in soil.

Unlike Nitrosomonas, the 10% seawater treatment did not stimulate Nitrobacter growth in soil. Both 20 and 40% seawater applications had rendered Nitrobacter numbers undetectable by the procedure employed at 42 and 28 days of incubation respectively. These results suggest the possibility of nitrite accumulation in soil. Consequently, phytotoxicity is likely to occur under such conditions.