Soil structure and salinity effects of fish farming as compared to traditional farming in northeastern Egypt

Recently, fish farming instead of traditional agriculture has been seen as a way to increase agricultural profits from saline affected land. Concerns, however, have been raised that fish farming may increase the salinity problems. In the salinity affected soils of the El-Salam canal project area in Egypt, farmers are giving up traditional farming for fish farming due to possibilities to increase their profits. The government, however, supports traditional agriculture in order to increase national income and secure food. The purpose of this study is to investigate and compare soil properties such as solute transport and soil salinity distribution for soil that has been used for fish farming as compared to traditional agriculture. This was done by dye experiments and salinity readings at three experimental plots located within El-Salam Canal project area. The first plot represents natural soil without human influence. The second and third plot was used for 3 years for fish farming and traditional agriculture, respectively. Each plot was irrigated with a solution containing dye tracer for 3 days. On the day following the last day of irrigation, a trench was dug and 10 cm thick vertical slices were excavated and photographed. Soil bulk salinity and pore water salinity measurements through a grid of 1 m width, 0.5 m depth, and 10 cm interval were taken. Soil samples were taken from different depths (10–50 cm). The dye pattern showed that solute transport at the fish farm site was small, reflecting low permeability. On the contrary, solute transport at the plot representing traditional agriculture was fairly large through the tillage layer (20 cm). Salinity maps showed that traditional agriculture contributes to decreasing soil salinity by about 70% and making soil more uniform in salinity distribution. Salinity maps at the fish farming plot site showed insignificant decrease in soil salinity. There was also a clear heterogeneity in salinity distribution. The results appear to show that fish farming does not contribute to decrease in the soil salinity. Thus, increasing fish farming activities may lead to increasing soil salinity problems in agricultural lands. The results showed also that there is no evidence that soil properties are enhanced by fish farming. On the contrary, the soil nutrient state appears to be decreasing.