Development of Magnesium Fertilizer Replacing Kieserite from Bio-Physico-Chemical Activated Dolomite

Abstract

All plants, especially cocoa and oil palm, require magnesium (Mg) along with other macro- and micro-nutrients. Kieserite as the most common Mg-supplying fertilizer for crops is still imported for Indonesia due to lack of natural deposits in the country. On the other hand, dolomites (CaMgCO3) are found abundantly and mostly used as liming material due to low MgO content and solubility as well. Many efforts have been carried out since a century ago to convert dolomite into Mg fertilizer substituting kieserite. However, there are no efficient processes available yet and therefore it is the objective of this study to develop a potentially efficient process by employing bio-physico-chemical activation approach in converting dolomite into kieserite-like product. A series of experiments were conducted by using a calcinated dolomite from Sidayu, Gresik, East Java, reacting with H2SO4, and inoculating with Mg-solubilizing microbes. An 80-mesh calcined dolomite powder was reacted with water at 1:3 ratio (% w/v) and after one hour stirring added with technical grade H2SO4 improving 27.7% MgO content from 18% to 23%. The formula was then tested its effectiveness for cocoa and oil palm seedlings in the greenhouse for three and six months, respectively. By combining NPK fertilizer at standard dosage with the formula of Mg-fertilizer at 75% of kieserite rate yielded the highest performances by six-month-old oil palm seedlings in a greenhouse experiment. To obtain conclusive results under field conditions, the formula was tested at field experiments using immature and mature oil palm trees. At 0.9 kg/tree/year dosage, the Mg-fertilizer formula was superior to conventional kieserite at 1.6 kg/tree/year rate in supporting vegetative growth of immature oil palm. From the mature oil palm trial, it can be concluded that the use of the new formulated Mg-fertilizer at 50% rate of conventional kieserite (2 kg/tree/year) resulted in an insignificant different yield of fresh fruit bunches (FFB) compared to standard kieserite dosage.