Effects of gypsum on saline and sodic soils


Soils become saline in many ways. Weathering of parent rock and lack of salt transfer due to low precipitation are the main reasons for primary soil salinity in arid and semi-arid regions. Salt accumulation caused by poor irrigation management and or use of low-quality water are among the major reasons for expansion of salinity in lands under irrigation worldwide. Salt transferred by wind from adjacent saline and dry areas and or by small drops of seawater to other areas and or salt transfer by groundwater under the influence of capillary forces also are important in some regions. Sequential increases in sodium and or removal of calcium due to lime precipitation in soil cause relative increases in sodium ions on soil particles and formation of sodic soils. Suitable irrigation water has calcium to magnesium ratios higher than 1. In some soils, excess magnesium acts as sodium and causes problems for soil structure and even for plant growth. As a source of available calcium, agricultural gypsum increases and modifies the calcium to magnesium ratio. The problem of disturbed calcium to magnesium ratio, which is observed in many soils, can be solved by applying gypsum.