Abstract
In a pot experiment brackish water (EC 2 dS tn-1, SAR 12, RSC 3 me L-1) with different Ca:Mg ratios (4:1, 2:1, 1:1, 1:4, 1:6) was applied to wheat and rice crops grown on a calcareous sandy loam saline-sodie soil. The results indicated that all the yield components of wheat LU 26S remained statistically similar. In rice, productive tillers and paddy yield decreased while sterility percentage increased significantly with a decrease in Ca:Mg ratios in the applied water. Percentage of Na and Mg increased while that of K and Ca decreased in wheat straw but Na increased in grain as the Ca:Mg ratio in irrigation water decreased. There was little effect of the tested irezuments on K, Ca and Mg concentrations in wheat grains. Concentration of Na in rice straw and paddy increased while that of K decreased statistically as the Ca:Mg ratio decreased. All the cations were present at much higher concentrations in straw of both the wheat and rice than thosein their economic produces.
INTRODUCTION
Groundwater is amongst the important sources of irrigation in Pakistan, i.e. 40 MAF water is pumped and used for irriga-tion (NCA, 1987), Out of the pumped groundwater about 75% is hazardous. Besides having a higher concentration of dissolved salts and SAR, these waters often have more Mg than Ca. The proportion of Mg generally increases with an increase in the EC and/or SAR of most of the ground-waters (Ahmad and Chaudhry, 1988). The continuous use of such poor qual-ity waters, those have higher proportion of Mg, influences adversely the properties of normal productive soils (Khan, 1975) and plant growth (Chaudhry ci at, 1986). It is still controversial whether Mg should be grouped with Ca or Na for calculating the
SAR and also for judging the quality of irri-gation waters. Some scientists (U.S. Salinity Lab. Staff, 1954; Ahmad et at, 1969) con-cluded that Mg acts like Ca in influencing the properties of soils only because of its di-valent nature. Others (Bohn et at, 1985; Kanwar and Chaudhry, 1968) believe that Mg should not be combined with Ca due to varying affinity for adsorption by the soil ex-change complex. Little work has been done regarding the effects of poor quality water with Mg higher than Ca on the soil and plant health particularly when soil is saline-sodic. Keeping these diverse opinions in view, the present studies were planned to observe the effects of low quality water with different Ca:Mg ratios on the growth characteristics of wheat and rice on a saline-sodic
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