Irrigation Water: Quality and Factors

After reading this article you will learn about the quality of irrigation water and factors affecting it.

Quality of Irrigation Water:

Whatever may be the source of irrigation water viz. river, canal, tank, open well or tube- well, some soluble salts are always dissolved in it. The main soluble constituent in water is Ca, Mg, Na and K as cations and chloride, sulphate bicarbonate and carbonate as anions.

However ions of other elements such as lithium, silicon, bromine, iodine, copper, cobalt, fluorine, boron, titanium, vanadium, barium, arsenic, antimony, beryllium, chromium, manganese, lead, selenium phosphate and organic matter are also present.

Among the soluble constituents, calcium, sodium, sulphate, bicarbonate and boron are important in determining the quality of irrigation water and its suitability for irrigation purposes.

However other factors such as soil texture, permeability, drainage, type of crop etc., are equally important in determining the suitability of irrigation water. The following are the most common problems that result from using poor quality water.

1. Salinity:

If the total quantity of salts in the irrigation water is high, the salts will accumulate in the crop root zone and affect the crop growth and yield. Excess salt condition reduces uptake of water due to high concentration of soil solution.

2. Permeability:

Some specific salts reduce the rate of infiltration into the soil profile.

3. Toxicity:

When certain constituents of water are taken up by plans which accumulates in large quantities and results in plant toxicity and reduces yield.

4. Miscellaneous:

Excessive Nitrogen in irrigation water causes excessive vegetative growth and leads to lodging and delayed crop maturity. White deposits on fruits or leaves may occur due to sprinkler irrigation with high bicarbonate water.

Factors affecting Suitability of Waters for Irrigation:

The suitability of particular water for irrigation is governed by the following factors:

1. Chemical composition of water (TSS, pH, CO₃, HCO₃, CI, SO₄, Ca, Mg, Na, and B).

2. Total concentration of soluble salts or salinity (EC).

3. Concentration of sodium ions, in proportion to calcium and magnesium or sodicity (SAR).

4. Trace element boron may be toxic to plant growth, if present in limits beyond permissible.

5. The effect of salt on crop growth is of osmotic nature. If excessive quantities of soluble salts accumulate in the root zone the crop has extra difficult in extracting enough water from salty solution, thereby affecting the yields adversely.

6. Besides this, total salinity depends of the extent to which exchangeable sodium percentage (ESP) of soil increase as a result of adsorption of sodium from water. This increase depends on sodium percentage.

7. Soil characteristics like structure, texture, organic matter, nature of clay minerals, topography etc.

8. Plant characteristics like tolerance of plant varies with different stages of growth. The germinating and seedling stages are usually the most sensitive to salinity.

9. Climatic factors can modify plant response to salinity. Tolerance to saline water irrigation is often greater in winter than in the summer. Rainfall is the most significant factor for the leaching of salts from the plant root zone. Temperature also plays a vital role.

10. Management practices also play great role. Wherever saline water is used for irrigation, adoption of management practices which allow minimum salt accumulation in the root zone of the soil is necessary.

The primary parameters that have to be considered to ensure effective irrigation management for salt control are the water requirement of crop and quality of irrigation water. Correct irrigation should restore any soil water deficit, to control salt levels.