Use of gypsum as an ameliorant of brackish ground water

Although Pakistan has the largest network of canal system in the world but, still, the river water supplies are insufficient to irrigate the cropped area under canal command. The canal supply, therefore, is supplemented with brackish ground water to fulfill the water requirement of crops. To minimize the harmful effects of brackish ground water, careful water management with suitable amendment is important. To address this problem a long term study was initiated during 1987, where gypsum on the basis of gypsum requirement of water considering the consumptive use of water of crops was applied to soil in maize- berseem-rice-wheat rotation. The quantity of gypsum based on its 50 and 100% requirement for one, two and three years at a time was applied in soil with 10 t ha-1 FYM and without FYM to neutralize the sodicity effects of ground water. The pH, ECe, and SAR of the original soil were 7.8, 2.8 dS m-1 and 10.9, respectively. The results of first phase of study (upto 1990-91) indicated that the application of gypsum with FYM reduced the SAR of the soil to 5.0 but ECe increased to 4.2 dS m-1. To reduce the ECe below 4.0 dS m-1, a heavy irrigation with canal water was applied to all plots before maize 1991, which reduced the salinity level in soil below 4.0 dS m-1. Then 40% leaching fraction was included in the second phase of study to maintain the salinity level in soil below 4.0 dS m-1. The application of additional 40% water as leaching fraction was started with berseem 1991-92 and continued upto wheat 1993-94. Unfortunately, the ECe could not be maintained below 4.0 dS m-1 with the addition of 40% an extra water, therefore, it was dropped during 1993-94 and the study was continued in third phase upto 1996-97 without leaching fraction with the same treatments. The average pH, ECe and SAR values after wheat (1996-97) in control were 8.27, 3.46 and 14.0, respectively; whereas in 100% gypsum + FYM treatment, these were 8.1, 3.96 and 6.97, respectively. During these three phases of study, recommended doses of fertilizers were applied to each crop. The yield data indicated that during the third phase, the yields of most of the crops were not significantly affected by the use of brackish water with gypsum + FYM. Thus, it is concluded that this type of brackish ground water may be successfully used with gypsum to keep the healthy salt balance in soil without deteriorating the crops yields.