Effect of Waterlogging Conditions on Some Chemical and Electrochemical Changes in Soil Solution of Calcareous Soils

In recent years, floods and waterlogging conditions in the northern and southern provinces of Iran have become important challenges, which directly and indirectly affect the solubility and availability of most of the soil nutrients. To investigate the effects of waterlogging, seven soils were selected from the orchards of different regions of East Mazandaran (Ghaemshahr, Sari, and Neka). In a pot experiment, the soils were placed under continuous waterlogging conditions for 70 consecutive days, and the trend of changes in oxidation-reduction potential (Eh), electrical conductivity (EC), pH, concentrations of Ca2+, K+, Na+ and iron (Fe2+ and Fe3+) of these soils were studied. The results showed that the mean Eh values of soils dropped within 2 days of waterlogging, then increased slightly in the third day, and then began to drop again, and this drop trend continued until the end of the period, from 552 mV at the beginning of waterlogging and reached -99 mV at the end of the period. The average soil pH decreased from 7.8 to 6.88 after 10 days of waterlogging, and then increased and reached a relatively stable equilibrium (about 7.05). The average EC values of soils, increased after the first day of waterlogging, then, declined to 2.13 dS/m, and again increased to the maximum value (about 3.09 dS/m) after 10 days. The concentration of Ca2+, K+, and Na+ in the soil solution increased after waterlogging and reached the maximum within 2 days, then gradually decreased and reached a relatively constant amount. The concentration of Fe within the first days after waterlogging was 1.95 mg/L, increased to 6.67 mg/L after 10 days, then decreased to 4.27 mg/L after 20 days, and eventually increased to 9.98 mg/L at the end of the period (70 days). Based on the results of this study and considering the trend of EC changes and concentrations of nutrients in soil solution, application of chemical fertilizers to soils should be avoided after waterlogging occurrence. Also, due to the changes in soil Eh, the continuation of waterlogging for more than 5 days can lead to relatively anaerobic conditions in the soil and damage to fruit trees, therefore, drainage of excess water is recommended.