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24 { THE SOMM JOURNAL } DECEMBER/JANUARY 2016/2017 { getting geeky } Vital in Viticulture A BRIEF STUDY OF NECESSARY NUTRIENTS IN VINEYARD SOILS: A FOCUS ON MAGNESIUM story and photo by Allyson Gorsuch DURING OUR SOMM CAMP SERIES, I have been visiting vineyards alongside viticulturalists, and like most topics in this beautiful business, the more I learn, the more I want to learn. In one particular article, the importance of magnesium in the soil led a reader to ask for clarification, as one authority mentioned vineyards not being planted on a hillside because it held too high a quantity of magnesium, while another leader spoke to a vineyard doing well because of its higher magnesium level. Simply put, like anything else in wine production, it is an overall balance that leads to the best product. But let's take a deeper look. Vines rely on six macronutrients in order to reach full poten - tial: nitrogen, phosphorous, potassium, calcium, magnesium and sulfur. The micronutrients needed include: iron, manganese, copper, zinc, boron and molybdenum. Nitrogen is the most important nutrient in vine growth and, along with phosphorous and sulfur, is considered an anion (pronounced ann-ı ¯on), meaning that it is negatively charged. Potassium, calcium and magnesium are cations (pronounced cat-ı ¯on), which are positively charged. The uptake of these positively charged nutrients in vineyard soils relies on the hydrogen content of the soil solution, which bonds with like positive ions (cations), referred to as the cation exchange capacity, or CEC. Cations present to hydrogen similarly, which means that they compete with each other for plant uptake. This means that a vineyard with a higher potassium content may take away from magnesium uptake; hence a vineyard high in potassium would benefit from a higher magnesium content. Too much magnesium overall, however, would displace the nitrogen, as well as make it more difficult to draw potassium and calcium; hence a vineyard too high in magnesium would not allow vine growth. Although vital to the production of chlorophyll, vines do not require as much magnesium, so monitoring its level is essential. The pH of a vineyard soil determines productivity: the lower the pH of the soil, the more hydrogen to bond with cation nutri - ents. A pH between 6 and 6.5 is ideal. Magnesium can reach the root at lower pH levels but in soils with a higher pH must be regulated so as not to interfere with the other cations. Only through attentive monitoring of the full nutrient content of the vineyard soils can balance be achieved for optimal growth and production. Balancing the cations depending upon the pH con - tent is key in avoiding nutrient deficiencies, and in establishing the optimal magnesium level. A close-up of vine- yards in the Saumur region of France's Loire Valley.