CONJUNCTIVE USE OF SALINE AND NONSALINE WATERS .2. FIELD COMPARISONS OF CYCLIC USES AND MIXING FOR WHEAT

To evaluate the changes in soil water and salinity when conjunctive irrigation with canal (CW, 0.6 dS/m) and saline (SW, 12 dS/m) waters is practised in various cyclic/mixing modes and their associated effects on growth and yield of wheat, field experiments were conducted during 1989-91 on a sandy loam soil. Normalising the treatment receiving canal water (100%), relative yield with saline irrigation was reduced to 60%. Substitution of canal water for saline water at pre-sowing stage improved seedling establishment and at first post-planting irrigation further enhanced tillering and related growth parameters, thereby, resulting in yield improvements by 18 and 16% over saline irrigation alone, respectively. Whereas cyclic irrigations with canal and saline water in 1 CW: 1 SW and 2 CW: 2 SW modes produced 7-11% more yields when compared with mixing in equal proportions (86%), yield was reduced by 12% in 1 SW: 1 CW mode, i.e. using saline water to start with. Use of canal water at the initial stages seemed to cause priming effect through increased soil water depletion. thus resulting in better growth rates (tillering) whereas adjustment to reduced salinity stress at later stages via increased grains/ear failed to totally compensate for losses due to reduced tillering. Stepwise linear response function with time averaged salinity (EC(e), dS/m) down to 1.2 m could be represented as: RY = 100 - 9.2 (EC(e) - 4.0). Multiple regression with dummy variables predicted EC50 (EC(e) for 50% yields) values to be 9.7, 11.9 and 16.7 dS/m, respectively, for salinity (0-0.3 m soil depth) at sowing, mid-season and harvest time indicating towards enhanced tolerance with ageing. It was concluded when making conjunctive use of canal and saline waters for the production of wheat, that higher efficiency of irrigation can be achieved with their cyclic use when canal water is applied at the initial stages (pre-irrigation and/first post-sowing irrigation) and saline water is used at the later growth periods when it can tolerate the salts better.