Why do some croplands suffer from excessive soil salinity?

Factors such as sea level rise, drought, usage of poor quality groundwater for irrigation and improper usage of fertilizers and pesticide has led to the soil become salt-affected. Salinization of farmland and limited fresh water access is threatening global food security and the livelihood of many farmers.
Salts occur naturally within soils and water. Salination can be caused by natural processes such as mineral weathering or by the gradual withdrawal of an ocean. It can also come about through artificial processes such as irrigation and road salt. Soil salinity can be reversed, but it takes time and is expensive. Solutions include improving the efficiency of irrigation channels, capturing and treating salty drainage water, setting up desalting plants, and increasing the amount of water that gets into aquifers. Mulches to save water can also be applied to crops. Salinity becomes a problem when enough salts accumulate in the root zone to negatively affect plant growth. Excess salts in the root zone hinder plant roots from withdrawing water from surrounding soil. This lowers the amount of water available to the plant, regardless of the amount of water actually in the root zone. If the level of salts in the soil water is too high, water may flow from the plant roots back into the soil. This results in dehydration of the plant, causing yield decline or even death of the plant. Crop yield losses may occur even though the effects of salinity may not be obvious. The excessive use of water for irrigation in dry climates, with heavy soils, causes salt accumulation because they are not washed out by rainfall. ... The practice of waterlogging without adequate drainage has also become a serious cause of soil salinization.