Effect of sustained saline irrigation on soil salinity and crop yields

Summary

Field studies were conducted for a period of ten years (1974 to 1984) on Typic Ustochrept to determine the sustained effects of saline irrigation water electrical conductivity (EC _iw ) 3.2 dS/m, sodium adsorption ratio (SAR) 21 (mmol/1)^1/2 and residual sodium carbonate (RSC) 4me/1, on the build up of salinity in the soil profile and yield of crops grown under fixed rice-wheat and maize/millet-wheat rotations. Saline waters were continuously used with and without the addition of gypsum (at the rate needed to reduce RSC to zero) applied at each irrigation. In maize/millet-wheat rotation, two additional treatments viz. (i) irrigation with 50% extra water over and above the normal 6 cm irrigation, and (ii) irrigation with good water and saline water alternately, were also kept. The results showed that salinity increased rapidly in the profile during the initial years but after five years (1979–1984) the average soluble salt concentration in 0–90 cm soil profile did not appreciably vary and the mean EC _e values under saline water treatment remained almost similar to EC _iw , under both the crop rotations.

Saline water irrigation increased pH and Na saturation of the soil, reduced water infiltration rate and decreased yields of maize, rice and wheat. The differences in the build up of salinity and ESP of the soil under the two cropping sequences seemed to be related with the differences in leaching that occurred under rice-wheat and maize/millet-wheat rotations. Application of gypsum increased the removal of Na from the profile, appreciably decreased the pH and Na saturation and improved water infiltration rate and raised crop yields. Application of non-saline and saline waters alternately was found to be a useful practice but irrigation with 50% extra water to meet the leaching requirement did not control salinity and hence lowered crop yields.