The poor drainage characteristics of the soils in Arkansas that allow them to be efficient for rice production also contribute to the problems associated with salinity. Salinity results from adding salt to soils, usually in irrigation water, faster than it is removed by natural processes, such as surface runoff and downward percolation. Irrigation water is the major contributor of soluble salts in Arkansas but excessive nutrient additions from fertilizers, manures or waste materials may also contribute to the accumulation of salts. The types of soluble salts that usually contribute to salinity problems include calcium, magnesium, sodium, chloride, sulfate and nitrate. In addition to the effect on rice production, irrigation water that contains excessive levels of chloride can lead to chloride toxicity in soybeans.
Rice is most sensitive to chloride and nitrate salts at the seedling growth stage.
Sodium problems are usually native to particular soils such as the Foley, Lafe, Hillemann and Stuttgart soil mapping units. However, isolated cases of water containing excess sodium have been observed. Excessive sodium may cause poor physical conditions of the soils which can interfere with crop stand establishment. Alkaline soils are created by irrigating with water that contains high concentrations of calcium and magnesium bicarbonate. It is possible to develop both salinity and alkalinity problems in the same field.