What substance is primarily of concern regarding the quality of groundwater used for irrigation?

Salts are primarily of concern regarding the quality of groundwater used for irrigation because they can accumulate in the soil and affect plant health. When irrigation water contains high levels of salts, it can lead to soil salinization, which reduces water availability for plants and can ultimately damage crops. High salinity can impair seed germination, stunt growth, and reduce crop yields. This issue is especially critical in arid and semi-arid regions where evaporation rates are high and salts can concentrate in the soil.

In contrast, while E. coli bacteria, pesticide residues, and nitrates are important pollutants that can impact water quality, they don't affect irrigation water quality to the same extent as salts do regarding widespread agricultural practices. Salinity’s long-term impact on crop productivity makes it a priority for managing irrigation water quality.