Magnesium Mg zinc Zn boron B and other micronutrients

Deficiencies of Mg, Zn and B may occur, but are not commonly encountered. Broadcast magnesite, dolomite or sulpomag (also called K-Mag) at 100-500 kg ha-1 (100-500 lb acre-1) of Mg provide an excellent long-term correction for soils deficient in Mg. For the immediate correction of Mg deficiency in pineapple, a series of foliar applications of magnesium sulphate (Epsom salts) are applied in combination with other sulphates, such as Fe or Zn. Cumulative amounts from repeated foliar sprays may range from 10 to 50 kg ha-1 (10-50 lb acre-1) of Mg in the plant crop and 5 to 25 kg ha-1 (5-25 lb acre-1) of Mg in the ratoon.

Since a deficiency of Zn or B can be especially devastating, they are applied when even marginally low levels are suspected. Zinc and boron are truly microelements and should not be overapplied. Zinc sulphate is applied in combination with other sulphates, such as Fe or Mg, to achieve a total application of no more than 0.1 kg ha-1 (0.1 lb acre-1) of Zn. Boron should not be applied in combination with any other nutrient; it should be applied at about 1.0 kg ha-1 (1.0 lb acre-1) of B in one or two foliar applications. Soluble forms of borax are available from qualified fertilizer dealers. In Queensland, Australia, boron is commonly applied in the ethephon solution at 10 kg acre-1 of borax or solubor, when plants are forced, to supply B and, especially when forcing in midsummer (January-February), to raise the pH of the ethephon solution to enhance forcing success. Under these conditions, boron is applied in a 2.0-4.0% urea solution.

Deficiencies of copper and molybdenum are also sometimes encountered (see Malezieux and Bartholomew, Chapter 7, this volume). Care should be exercised when applying these micronutrients because their use in areas not showing deficiency could result in foliar damage due to toxicity.

Growing Soilless

Growing Soilless

This is an easy-to-follow, step-by-step guide to growing organic, healthy vegetable, herbs and house plants without soil. Clearly illustrated with black and white line drawings, the book covers every aspect of home hydroponic gardening.

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