Field experiments were conducted with potato as test crop in acid soils of Shillong and Shimla during 1980 to 1983 to investigate the effect of different Mg-salts on the efficiency of ammonium sulphate, mea and calcium ammonium nitrate. On the soils of Shillong (pH 4.9 to 5.0), the application of Mg as MgSO4 or Mg(NO3)2 had, no positive effect but the application as MgCO3 improved the tuber yield. The improvement due to MgCO3 varied with the source of N. It was of the order of 13.5% with ammonium sulphate and 23% with mea. The application of MgCO3 also showed more improvement in the uptake of N, P and Mg by tubers with urea than with A/S. In the soil of Shimla (pH 6.1), the application of MgSO4 did not improve tuber yield but increased tops/tubers ratio. It had no effect on the efficiency of calcium ammonium nitrate.
