SOIL PREPARATION

iii) Saline-sodic soils have EC e < 8.5 per definition. Such soils contain both too much salt as well as too high a Na concentration while free lime and gypsum often occur. Saayman (1981) recognised a further two classes of brack soils namely an acid sodic soil and an acid saline-sodic soil. Both these types of brack soils have an ESP > 15 %, contain no free gypsum and/or lime and have a pH H 2 O < 7.0. Acid sodic soils, however, have an EC e < 400 mS/m while the EC e of an acid saline- sodic soil is more than 400 mS/m. Saayman (1981) also reported the occurrence of both these types of acid brack soils in the Breede River valley, Little Karoo, Olifants River valley and the Coastal region of South Africa. 6.5.2 Reclamation measures Soil reclamation is the restoration of poor physical and chemical soil properties to a state that is beneficial to production. As a first step in the reclamation of brack soil, it is recommended to stop the source of salts, e.g . by installing cut- off drains and ensuring that leaking dams and canals are repaired. If compact soil layers occur within a meter of the surface, they must first be broken up by suitable deep tillage to allow water to penetrate properly. Subsequently subsurface drains can be put in to remove salts that are leached. White brack soils, particularly if they contain free lime or gypsum, are the easiest to reclaim. A few heavy irrigations would suffice to leach the excess salts into the drainage system. In the case of sodic soils and saline-sodic salts that contain no gypsum or lime, gypsummust be applied before attempting to leach the soil. Gypsum (CaSO 4 ) is a source of Ca and its application to the soil aims to replace harmful Na with beneficial Ca. Gypsum has, however, a low solubility and needs both large volumes of water and time to dissolve and do its work. The incorporation of organic material into the soil together with gypsum will also help to improve water infiltration and allow gypsum to leach into the subsoil (Van Woerkom & Streutker, 1971). Molasses has also been used successfully on a saline-sodic soil to improve water infiltration (Weber & Van Rooyen, 1971). Molasses improved water infiltration much sooner than sulphur and gypsum that reached their maximum effect only in the second year after application (Van Rooyen & Weber, 1972). Good water infiltration allows rain and irrigation water to move through the soil pores and wash out excessive salts and displace Na from the soil profile into the drainage system. Acid sodic and acid saline-sodic soils can be reclaimed by applications of lime and leaching (Saayman, 1981). He mentioned that farmers solve the problem practically in the Bonnievale area by using crawler tractors to mix lime- containing “heuweltjies” (little hills) with surrounding acid sodic soil. Soil can be reclaimed by lime application and leaching. > 400 mS/m an ESP > 15 % and pH H 2 O

106 | SOIL DRAINAGE