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Subject

Magnesium

Description

Magnesium deficiency: A pronounced pattern of whitish or creamy yellow color appears between veins.

Magnesium (Mg) deficiency is a very minor nutritional problem in vineyards. Symptoms develop infrequently and are usually mild. The most common problem is the confusion of Mg deficiency with other nutrient deficiencies, notably potassium (K). The plant needs Mg to activate many enzymes required for plant growth and as a structural component of compounds needed in protein synthesis. It is a primary constituent of the chlorophyll molecule, so deficiency causes leaf chlorosis.

Magnesium is moderately leachable in soil and, as with calcium (Ca), greater amounts are often found in the subsoil than in upper parts of the soil profile, especially on older, highly weathered soils. Magnesium deficiency is more prevalent on old, leached hardpan soils, wind-modified sandy soils, and recently reclaimed alkali soils. Fill areas from land leveling are more susceptible due to the further burying of the higher-Mg subsoil. Likewise, young vines are more deficiency-prone until their root systems penetrate subsoils.

Magnesium is mobile within the plant and, under deficient conditions, is readily translocated from older to younger tissue. Thus, older basal leaves show the first signs of chlorosis, usually in mid- to late summer. The chlorosis begins at or near the leaf edge and progresses inward between the primary and secondary veins. Some border of green color remains along the main veins; the chlorotic area may become almost creamy-white. The remaining green tissue surrounding the main veins is best described as a "Christmas tree pattern." The chlorotic margins can become necrotic and turn brown as the deficiency becomes more advanced.

People

Doug Adams
L. Peter Christensen
Donna Hirschfelt
William L. Peacock
Rhonda Smith
Larry Williams

Publications

Christensen, L.P. 2000. Mineral Nutrition and Fertilization (PDF). Pages 102-114 in: Raisin Production Manual. University of California, Agricultural and Natural Resources Publication 3393, Oakland, CA. Buy book

Christensen, L.P. 1984. Nutrient level comparisons of leaf petioles and blades in twenty-six grape cultivars on three years, 1979-1981. Am. J. Enol. Vitic. 35:124-33. Abstract

2004. Soil Environment and Grapevine Mineral Nutrition Symposium. Proceedings of the American Society of Enology and Viticulture. To Purchase

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