One factor that farmers frequently fail to consider is water quality used for irrigation. Water that looks clear is generally taken to be safe, however, dissolved salts, wrong pH, and toxic ions can weaken the growth of the crop without any symptoms being visible. A study indicates that irrigation water having an electrical conductivity of only 1. 0 dS/m is a source of nearly one ton of salt per acre, foot, which is steadily increasing in the soil. Consequently, salinization now affects approximately 20% of the world’s arable land and nearly one, third of the land that is irrigated. This slow, invisible accumulation makes poor water quality one of the most unrecognized threats to agricultural productivity.
Poor-quality irrigation water can lower crop yields through a process that is very potent albeit rather slow. High levels of salts build up in the root zone and cause osmotic stress that ensures that despite the moisture content, the crop is not able to take much water. Yield reduction is shown when salinity levels above or around 4 dS/m are attained, though crop such as beans and strawberries is affected at much lower levels. Results from the use of poor-quality irrigation water on spring maize yield showed significance when the salinity levels were set between3.5 and 5.0 g/L.
“The effect becomes stronger over time.” Field tests conducted showed that soil salt levels in cotton crops irrigated with saline water increased between 5% and 150% in soil up to three meters below the soil surface in soil with high salt concentrations. This is soil degradation and will take many years to reverse, unlike transient soil tension caused by surface irrigation.
The critical levels of crop tolerance make the risk inevitable. In sensitive vegetables, the irrigation water is harmful beyond 1.5 dS/m, moderately sensitive vegetables beyond 3 dS/m, and even salt-tolerant vegetables beyond 6 dS/m. Toxic salts accelerate the deterioration that is, onions, beans, and lettuce get adversely affected due to boron contents beyond 0.5 ppm, while potatoes get harmed due to contents beyond 0.7 ppm.
Water pH is equally important to crop performance as salinity is, because it has a major impact on nutrient availability. Generally, most crops grow best if the irrigation water used has a pH of between 6. 0 and 7. 5. Acidic water releases a higher amount of aluminum and manganese ions, among other, which in turn, damage the root system and at the same time, nutrients absorption becomes inefficient. On the other hand, alkaline water above pH 7. 5 limits a number of essential micronutrients such as iron, manganese, zinc, and copper, thus chlorosis, lack of growth, and yield reduction may occur even when nutrient, rich soils are present.
The problems are getting worse and worse with each irrigation cycle. The use of alkaline water results in a gradual increase of soil pH, which is more of a problem in container systems or fields under intensive irrigation. Research finds that by increasing the alkalinity in irrigation water over 150 mg/L causes substrate pH to rise to the point that iron and manganese deficiencies occur, calcium and magnesium balance is altered, and plant quality and quantity are lowered, in the end, the most likely crops to be affected are those which are cultivated intensively for food or cut flowers.
The chemical changes that underlie these losses are quite predictable. For instance, the availability of Phosphorus is highest around pH 6. 5 but it lowers rapidly when pH is below 5. 5 or above 7. 5 due to attachment to aluminum, iron, or calcium compounds. Also, soil micronutrients behave similarly, and at each subsequent pH increment from the optimal range to that of the unsuitable irrigation water, they become less and less accessible.
Irrigation can act as both a lifeline and a liability. When water quality is poor, it suppresses crop yields while steadily degrading soil structure, altering beneficial microbial populations, and triggering long-term fertility decline. Research shows that average farm yields reach only 20–50% of their recorded potential, with much of this gap driven by environmental stresses like poor irrigation water quality among the most persistent, an issue expected to intensify under climate change.
