Secrets to Transforming Poor-Quality Irrigation Water into Garden Gold!

Continuous irrigation with saline water leads to the accumulation of salt in the soil which adversely affects soil health and gradually reduces crop yields. In about 40% of the total area of Punjab, especially in south-western districts, the underground tubewell waters contain high salt concentrations. These waters are either saline (containing chlorides and sulphates of sodium) or sodic (containing carbonates and bicarbonates of sodium).

Some of these waters may also contain toxic elements like boron and fluoride. Therefore, it is essential to conduct tests on tubewell water before using it for irrigation. Knowing the kind and extent of the problem of water contamination helps in adopting specific management practices to mitigate its harmful effects on soil fertility and crop productivity. Classification of irrigation water based on EC and RSC is given in Table 1. Moreover, the following guidelines are recommended for their safe use:

Adequate Drainage: In regions where irrigation water quality is subpar, it is crucial to leach out excess soluble salts and water from the root zone of the soil to maintain a favorable balance of salt and water. In areas with inadequate drainage and soils containing hard pans at certain depths, long-term irrigation with poor-quality water leads to a quicker accumulation of salts in the soil compared to well-drained soil conditions. Therefore, ensuring proper drainage is essential when utilizing poor-quality water for irrigation.

Proper Land Levelling: To achieve uniform distribution of irrigation water across the field, it is essential to properly level the land. Adequate land leveling guarantees consistent leaching of soluble salts and water from the soil. Even minor variations in microrelief within the field can lead to uneven distribution of water and salts.

Poor Quality Water on Light-Textured Soils: Light soils allow salts accumulated by irrigation water to be leached effectively due to their high infiltration rates. Conversely, heavy soils have low infiltration rates, causing water from irrigation to stagnate on the surface for extended periods. This prolonged exposure, coupled with evaporation, accelerates the accumulation of salinity and sodality in these soils. Hence, it is advisable to prioritize the use of poor-quality water on light soils.

Selection of Appropriate Crops: It is always preferable to grow crops and varieties capable of producing high yields even when irrigated with saline or sodic waters. Only salt-tolerant and semi-tolerant crops like barley, wheat, mustard, guar, senji, spinach, turnip, sugarbeet, raya, and millet should be grown. Pulse crops are sensitive to salinity and sodicity and, therefore, should not be irrigated with poor-quality waters.

Usage of Gypsum when Required: It is often observed that to reduce the impact of saline water, farmers must use gypsum without testing the soil and water. However, salinity effects are often encountered. Therefore, it is recommended to use gypsum when the RSC of irrigation water exceeds 2.5 me/l., based on the examination of soil and water. The quantity of gypsum should be calculated from a water test report.

Including Organic Manures: In calcareous soils with more than 2% calcium carbonate, organic manures viz. farmyard manure @ 8 tonnes/acre or green manure or wheat straw @ 2.5 tonnes/acre/year should be used for reducing harmful effects of sodic irrigation water.

Mixing Poor and Good Quality Waters: This approach becomes crucial, especially in scenarios where there is an insufficient supply of good-quality canal water. The poor-quality waters should preferably be used to supplement the good-quality canal waters. The poor and good quality waters can be used together, either alternatively or by mixing. Additionally, it is advisable to use good-quality waters during the initial stages of crop growth and switch to poor-quality waters during later stages when the crop can withstand higher levels of salinity or sodicity.

Village Pond Water for Irrigation: Water in village ponds contains essential plant nutrients like nitrogen, phosphorus, potassium, etc. However, it may also contain salts such as carbonates, bicarbonates and chlorides of calcium, magnesium, and sodium in undesirable amounts. Therefore, this water should be tested by the Soil and Water Testing Laboratory and may be used for irrigation as per recommendation.

Utilizing Poor-Quality Irrigation Water for Cotton Cultivation: Cotton is sensitive to poor-quality water at the germination stage but can be grown if proper germination is ensured. In cotton growing areas where underground irrigation water is of poor quality, prefer ridge planting of cotton using pre-sowing irrigation with canal water and subsequent irrigations with poor quality tube well water in alternate furrows for sustainable yields. The alternate furrow irrigation with poor-quality tube well water also results in saving irrigation water and checking the deterioration of soil health. Besides, under a scarcity of good quality irrigation water, alternate use of good quality canal water and saline tubewell water through surface drip irrigation is recommended in light-textured soil for obtaining sustainable seed cotton yield with a minimal adverse effect on soil quality. In soils irrigated with saline water (EC upto 10 dS/m), the application of 16 quintals per acre of rice-residue biochar reduces the adverse effect of salinity and increases seed cotton yield.

By considering these points, the impact of poor-quality water can be significantly reduced. Moreover, when poor-quality waters are used on a long-term basis, the farmers should keep a watch on the build-up of salts in the soil by getting the soil samples tested at regular intervals. This will help them in keeping a check on soil deterioration.

Table 1: Quality of irrigation water based on Electrical Conductivity (EC) and Residual Sodium Carbonate (RSC) concentration