Effectiveness of calcium amendments to alleviate subsoil acidity than magnesium amendments in Ultisols

Abstract

The growth of oil palm production in Malaysia is seriously inhibited by subsoil acidity. Correcting subsoil acidity, along with an increase in Ca2+ in the subsoil, requires a decrease in Al3+ concentration. There are few effective methods for subsoil acidity fixation. Due to its slow downward movement, dolomite applications, while effective in correcting surface soil acidity, have little effect on subsoil acidity. A column leaching experiment was performed to investigate the amelioration effects of calcium hydroxide (Ca(OH)2) (HL), calcium oxide (CaO) or calcium carbonate (CaCO3) (CC) compared to dolomite (DL) and gypsum (GY) with surface application order to improve low cost and effective methods for the amelioration of subsoil acidity by surface application of modifications. Soil solution analysis findings have shown that surface-applied Ca2+-amendments can be used effectively to correct the acidity of the subsoil. These Ca2+-amendments more efficient than Mg2+ amendments in increasing soil solution pH, base saturation, soluble Ca2+, and decreasing soil solution Al3+, reducing exchangeable acidity to varying degrees for different segments of the soil profile. The high soluble Ca2+ content in the soil solution was also higher in Ca2+-amendments than in the soils that were unamended and modified by gypsum and dolomite. High soluble Ca2+ content of Ca-amendments facilitated the migration of base cations through the soil profile, the exchange of base cations with interchangeable aluminum (Al) and manganese (Mn), and the leaching out of the profile of soluble Al and Mn. Although the soil exchangeable Ca be increased by GY and DL, both of them also substantially increased the soluble Al and Mn about and 1.2 3 mmol-1 in the Ultisol profile. Besides, HL was, however, more effective in decreasing soil acidity and soluble Al and Mn increasing exchangeable Ca by about 23% compared to GY and DL in the Ultisol profile. Therefore, in improving soil acidity in the surface soil and subsoil of this Ultisol, HL was superior to GY and DL.