In India, Coffee is cultivated in a few pockets in the States of Tamil Nadu, Karnataka, Kerala, Andhra Pradesh, and the North East. Depending on the region, coffee cultivation is subjected to different agro-climatic zones and the soil types vary from region to region. Some zones have sandy loam, others clay, and a few others laterite soil. Soil analysis reports suggest that no soils have the correct amount of major, secondary or micronutrients for balanced crop production. This is especially true of magnesium, a secondary element, necessary for providing increased crop productivity. Coffee is one of the most sensitive crops to either too much or too little magnesium. Either situation will reduce both quality and yield potential.
Mg is a common constituent in many minerals, comprising 2% of Earth’s crust. The availability of magnesium in the soil is through the weathering of rocks.
Magnesium is found in a wide variety of minerals.
Neal Kinsey reports in his paper titled “The Role of Magnesium in Improving Crops and Yields”, quote “Adding too much magnesium to the soil can also result in a shortage of some other nutrients—generally potassium, sodium, calcium, or some combination thereof as well as reducing trace element availability. And depending on the source, using dolomite lime for example, that problem will not become completely evident for a full three years from the time it is applied. So, it is important to be sure that what you add is only what the soil actually needs.
Mark this and do not forget it when you strive to grow nutrient-dense foods: When there is too much magnesium in soil, the crop growing there will not get enough. Yes, crops growing on soils that contain an excess of magnesium will not get enough and will be short of magnesium that is actually needed to supply the best nutrition, the most efficient use of fertilizer and the best growth.
Adding more magnesium to a soil that is already too high in magnesium does not solve such a problem, it only makes the problem worse. In such cases, foliar applications are recommended, but it usually requires multiple applications to move magnesium into the specified high range on plant or tissue tests.”
How to calculate Magnesium addition to soils
The desired amount of magnesium can be established in pounds per acre by multiplying the soil’s total exchange capacity (TEC) times the atomic weight of magnesium in milliequivalents (240) times the desired percentage of magnesium.
Sandy loam soils are generally poor in Magnesium. Unlike other cations, Mg is very mobile in soils because it is less bound to the soil charges. Therefore, Mg losses by leaching might occur in sandy soils with high water conductivity. Leaching of Mg in soils, when applied with various water-soluble fertilizers, may also vary depending on the fertilizer’s chemical composition, granule size, and effect on soil pH and cation balance
How to overcome the deficiency
Liming materials such as magnesite, dolomite, and lime are insoluble and are slow to react in the soil. To be effective, they must be finely ground, i.e. have a fine particle size. In annual crops, they should be applied several months before planting and be incorporated into the soil.
Magnesium (Mg) is one of the six macronutrients that, along with nitrogen, phosphorus,
potassium, sulfur, and calcium, are taken up in the largest quantity by plants from the soil. About 5% of the total is present in exchangeable forms. This consists of magnesium held on clay and organic particles in the soil, and any magnesium in water-soluble forms.
Exchangeable magnesium levels are likely to be lower on well-drained sandy soils in areas of high rainfall where magnesium and other cations, e.g. calcium, have been leached from the topsoil. The role of magnesium has often been overlooked in the coffee Agroforestry system. There’s not an iota of doubt that magnesium plays a pivotal role in increasing crop productivity. But it is crucial to understand that the amount of magnesium released from the soil is inadequate to sustain high crop yields. Hence, external application of magnesium fertilizers, in the right quantity and proper time is crucial to improve productivity.
Anand T Pereira and Geeta N Pereira. 2009. Shade Grown Ecofriendly Indian Coffee. Volume-1.
Anand Titus Pereira & Gowda. T.K.S. 1991. Occurrence and distribution of hydrogen dependent chemolithotrophic nitrogen fixing bacteria in the endorhizosphere of wetland rice varieties grown under different Agro climatic Regions of Karnataka. (Eds. Dutta. S. K. and Charles Sloger. U.S.A.) In Biological Nitrogen Fixation Associated with Rice production. Oxford and I.B.H. Publishing. Co. Pvt. Ltd. India.