LAUSR

ABSTRACT Effect of magnesium chloride (MgCl2) and dolomite on magnesium (Mg) availability cassava was observed by a pot experiment under greenhouse condition in three Paleustults. Their water solubilities varied greatly, with increased Mg availability in the soils. This resulted in cassava taking up more Mg and producing 23.3–45.2% and 18.8–26.2% greater aboveground biomass over the control when respective MgCl2 and dolomite were added. Without Mg fertilization, Mg contents, mainly in a component of minerals, were low and constant throughout 120 days of the study, indicating that initial Mg content in these soils was insufficient for cassava growth. Magnesium became available at 1-month after dolomite was applied. Magnesium in MgCl2-added soil was predominated by available Mg; moreover, MgCl2 evidently boosted the soluble Mg portion within 15 days after applying. After that, the proportion decreased similarly to that of the other treatments. It indicated that dolomite was a better Mg source in supplying Mg for a longer period than MgCl2. In addition, the Mg contents in the soils gradually increased early and then sharply decreased at 30 days, and then the contents were constant until the end of the study. The result clearly signified that cassava absorbed Mg rapidly within 1.5 months after planting. Among soil extractants tested in the study, 0.05 M HCl was the best available Mg extraction suitable for cassava crop, whereas 1 M NH4OAc, the routine soil test in Thailand, was the least suited extractant.