Phosphogypsum applied in surface and mixed at soil on hydraulic conductivity, pH and leaching of sodium of one saline sodic soil

Abstract

Samples of a saline-sodic soil (of the Irrigated Perimeter of São Gonçalo, Souza towm, Paraiba State - Brazil) that has 61.25 me/100 of exchangeable sodium, were collected at depth 0-30 cm and phosphogypsum was applied in two levels (50% and 100% of the gypsum requirement - GR of the soil). The study v;as realized with the soil put in column of paltic tuble of 40 cm of tall and 5 cm of diametr. Both the quantities of the phosphogypsum (31 g (level-50% GR) and 62 g (level-100% GR)) were applied in the surface of the soil and too incorporated at depth 0-15 in such column. The water volume applied was 314 me and the time for star and the finish the leaching was read for to evaluate the hydraulic conductivity. In the end of the leaching each column was dismonted and divided in six parts of 5 cm that were made saturation extracts (1:5) of where were determinated pH, electric conductivity, soluble sodium content and the remaining sodium percentage (RSP). The data evidencied positive effects of the phosphogypsum on hydraulic conductivity of the soil, especially when the chemical corretive was incorporeted at 15 cm under surface of the soil. The hydraulic conductivity (k) valours showed that the less level (50% GR) was more efficient than great level (100% GR of the soil). The data of k for the phosphogypsum incorporated were 2.45 cm/h (level-50% GR) and 1.41 cm/h to level 100% of the gypsum requirement of the soil. In spite the chemistry aspects the electric conductivity data, soluble sodium contents and calours of remaining sodium percentage (RSP) of each interval of 5 cm of the columns , indicated that the phosphogypsum were more efficient in the displacement of exchangeable sodium when it was appliaed in the susrface of the soil. This way the chemical corretive showed to exercise differenced behaviour on physical and chemical properties of the soil alike its way of applications at soil.