Chemical Compositions and Salinity Development in Paddy Soil as Affected by Irrigation Intervals of Mixed Water under Saline Soil
ABSTRACT The northern Nile Delta, in Egypt, is an area with extensive saline soils with high ESP and EC. It was necessary to study the behavior of soil chemical compositions and soil salinity development under different irrigation intervals of mixed water (50% fresh + 50% drainage water). Two field experiments were carried out through two seasons. Four irrigation intervals viz; 3, 6, 9 and 12 days were applied under saline soil. The soil was chemically analyzed both before sowing and at the end of the season. Electrical conductivity, pH, Na, Cl, K, Ca, Mg, SO4, Na/K ratio and Na/Ca ratio as well as grain yield and its components were determined. The irrigation intervals significantly affected all the above mentioned characters except pH and Na/Ca ratio. Prolonging irrigation intervals markedly increased soil salinity, Na, Cl, K, Ca, Mg, SO4, Na/K ratio and SAR. Continuous irrigation succeeded in improving soil salinity and reducing its soluble salts. At the same time, grain yield was dramatically affected by prolonging irrigation interval in parallel with soil deterioration. The rice grain yield significantly decreased as irrigation intervals were prolonged up to 12 days. The data collected on salinity development during three months indicated that the prolonging irrigation intervals up to 12 days significantly increased the salinity level, particularly during July. High temperature and high evaporation during July led to high salts concentration in the soil. These results confirmed that the prolonging irrigation interval (12 days) under saline soil is unfavorable for rice growth. Looking at the rising of rice yield and soil chemical composition, it can be observed that flooding every 3 or 6 days should be followed to prevent the soil chemical composition from degenerating and unbalance nutrients.