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  • Writer's pictureJere Folgert

Garlic Needs Boron, Sulfur, Zinc, Copper, and Iron too.

Updated: Feb 15, 2023

Nitrogen (N), Phosphorus (P) and Potassium (K) are the three most important elements needed by plants. Sulfur is considered the 4th Major Nutrient for Plants. Sulfur is classified as a secondary element, along with Magnesium and Calcium, but it is sometimes called “the 4th major nutrient” because some crops can take up as much sulfur as Phosphorus. Carbohydrate, protein, and chlorophyll formation is significantly reduced in zinc-deficient plants. Therefore, a constant and continuous supply of zinc is needed for optimum growth and maximum yield. Copper (Cu) is one of eight essential plant micronutrients and is required for many enzymatic activities in plants and for chlorophyll and seed production. A deficiency of copper can lead to increased susceptibility to diseases. In plants, iron is also required for photosynthesis and chlorophyll synthesis. The availability of iron in soils dictates the distribution of plant species in natural ecosystems and limits the yield and nutritional quality of crops. Boron (B) is one of the essential nutrients for the optimum growth, development, yield, and quality of garlic crops. Boron performs many important functions in plants and is mainly involved in cell wall synthesis and structural integration


It is critically important to understand that too much of a good thing can really cause problems with your garlic plants. In other words, too much Boron, Zinc, Copper, Iron, and Nitrogen can ruin an entire garlic crop. Too much Boron can cause plant toxicity. In garlic, boron toxicity symptoms appear in young, expanding leaves. Symptoms can include misshapen plants. In any plant, excess boron can cause a variety of nasty issues. Severely affected plants can die. It is also very important the understand that nutrient supply to garlic plant roots is a very dynamic process, and the nutrients available to garlic roots are controlled by numerous chemical, physical and biological properties. As garlic plants absorb nutrients, the nutrient concentrations in the soil decrease.


Micro-nutrients play a vital role in the growth and development of garlic plants and garlic bulbs. The minerals BORON (B), COPPER (Cu), ZINC (Zn) and IRON (Fe) are necessary for several enzymatic and biochemical events within the plant. Boron deficiency is highly prevalent in sandy acidic soils with low organic matter, due to the potential for B leaching. Be careful, as too much Boron can cause plant toxicity.


"Phosphorus and zinc fertilizers are rarely required for growing garlic. Only moderate amounts of nitrogen are needed for top yields..." Read more from the article published by Kent B. Tyler, Donald M. May, John P. Guerard, David Ririe and James Hatakeda. Diagnosing nutrient needs of garlic. Phosphorus and zinc fertilizers are rarely required for garlic crops. Only moderate amounts of nitrogen are needed for top yields. (Source: the University of California Agriculture. https://calag.ucanr.edu/download_pdf.cfm?article=ca.v042n02p28)


There are only a few studies on the effects of micronutrients effects on the growth of garlic plants. Much of the research on growing garlic is limited to the recommendation for major nutrients. The three numbers on fertilizer represent the value of the three macro-nutrients used by plants. These macro-nutrients are nitrogen (N), phosphorus (P), and potassium (K), or NPK for short.


A study published by the USDA, provides data on the effects of excess Boron (B) on garlic (Allium sativum L.) and onion (Allium cepa L.) and investigated their Boron tolerances as measured by yield and quality of the marketable product. Zinc, copper, boron, and molybdenum played an important role in increasing the growth and bulb yield of garlic. Boron Deficiency in Garlic. Boron deficiency has been reported to cause the leaves to bend backward and to impair the storage properties of the bulbs. Boron treatments were imposed by irrigation with culture solutions that contained 0.5, 1.0, 5.0, 10.0, 15.0, or 20.0 mg B/liter. Relative yields of garlic and onion were reduced 2.7% and 1.9% with each unit (mg·liter-1) increase in soil solution B (BSW) above 4.3 and 8.9 mg B/liter, respectively. Increasing BSW reduced garlic bulb weight and diameter but did not significantly affect onion bulb weight or diameter. Boron concentration in leaves and bulbs was directly correlated to BSW.


Boron (B) is a micronutrient critical to the growth and health of all crops. Too much can be toxic to plants. It is a component of plant cell walls and reproductive structures. It is a mobile nutrient within the soil, meaning it is prone to movement within the soil. Because it is required in small amounts, it is important to deliver B as evenly as possible across the field. Traditional fertilizer blends containing B struggle to achieve uniform nutrient distribution. Despite the need for this critical nutrient, B is the second most widespread micronutrient deficiency problem worldwide after zinc. Boron plays a key role in a diverse range of plant functions including cell wall formation and stability, maintenance of structural and functional integrity of biological membranes, movement of sugar or energy into growing parts of plants, and pollination and seed set. To determine a plant’s B nutrient status, younger leaves are recommended for sampling and analysis. Typically, adequate B levels in dried leaf tissues range from 25 to 75 ppm B, which is a considerable quantity for many crops. Generally, a soil application of B is recommended when leaves contain less than 25 ppm Billion. Most crops are not able to mobilize B from vegetative tissues to actively growing, meristematic plant tissues such as shoots, root tips, flowers, seeds, or fruits. Rather, B transport occurs primarily in the xylem channel, resulting from transpiration. Because of this, deficiency symptoms first develop in newly developed plant tissue such as young leaves and reproductive structures


Boron deficiency is highly prevalent in sandy acidic soils with low organic matter, due to the potential for B leaching. Soils with high adsorption and retention capacity (e.g., soils with high pH and rich in clay minerals and iron or aluminum oxides) are also commonly impacted by B deficiency. In most crops, B shows very poor phloem mobility. Consequently, B in leaf tissue cannot be transported sufficiently into the reproductive organs (i.e., shoot tips, buds, flowers, seeds, etc.). Because of this poor mobility, keeping soluble B in soil solution during all stages of plant growth, particularly during reproductive growth (e.g., during seed setting), is critical for optimal plant nutrition. Environmental factors that reduce transpiration, such as high air humidity and low soil moisture, have adverse impacts on xylem transportation of B. Extended periods of drought impede B uptake by reducing root growth, limiting the supply of B from organic matter reserves, and by depressing diffusion and transport of B to root surfaces. Plants under low B supply are more susceptible to damage from high light intensity associated with long and hot, sunny days (see Picture 3). Under B deficiency, use of absorbed light energy in photosynthesis is significantly reduced, leading to an excess amount of energy and potential for leaf damage. Low soil temperature can also reduce root boron uptake.


Sufficient Boron is needed for Better Root Uptake of Phosphorus and Potassium. Studies show that adequate Boron nutrition improves root uptake of phosphorus (P) and potassium (K) by maintaining proper function (through ATPase activity) and the structure of root cell membranes. Boron has an important role in the colonization of roots with mycorrhizal fungi, which contributes to root uptake of P. In short-term experiments with corn plants, reduced root uptake of P and K under low B supply was restored within one hour after B was added to the growth medium. Experimental evidence also suggests that an adequate B supply is needed for the mitigation of aluminum toxicity in plants grown in low-pH soils. Tips for Preventing Boron Deficiency: Soil-test your fields every two years to gain a thorough understanding of the nutrient levels of your field. Make sure to compare your yield goals with current nutrient needs, and discuss options with an agronomist. Because there is a fine line between deficiency and toxicity, it’s important to apply the correct amount of B at the right rate using the right source. Aspire® with Boron ensures uniform nutrient distribution across each field.


Too Much Boron can be Toxic. Boron toxicity symptoms usually aren’t the result of small amounts of boron generally found in soil. However, some areas have boron in the water in high enough concentrations to cause boron toxicity in plants. Plants with too much boron initially display yellowing or browning of foliage. Leaf tips become dry, with the symptoms eventually taking over entire leaves. Boron, applied in irrigation water (BiW), will concentrate in the soil profile as other solutes do. The rate at which B concentrates depends on soil properties, the amount of irrigation water applied, the leaching fraction, and the B concentration in the irrigation water(Rhoades, 1982). Some of the B is adsorbed by fine soil particles, and an equilibrium is established between the adsorbed B and the dissolved B in the soil solution (BSW) (Eatonand Wilcox, 1939; Hatcher and Bower, 1958).


Zinc is an important component of various enzymes that are responsible for driving many metabolic reactions in all crops. Growth and development would stop if specific enzymes were not present in plant tissue. Carbohydrate, protein and chlorophyll formation is significantly reduced in zinc-deficient plants. What happens if a plant lacks zinc? The physiological stress caused by Zn deficiency results in the development of abnormalities in plants. In case of severe 'acute' Zn deficiency, visible symptoms include stunted growth, chlorosis of leaves, small leaves and sterility. Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodic table.


Copper is one of eight essential plant micronutrients. Copper is required for many enzymatic activities in plants and for chlorophyll and seed production. A deficiency of copper can lead to increased susceptibility to diseases like ergot, which can cause significant yield loss in small grains. In most plants, young foliage is severely stunted as well as chlorotic. Deficient foliage can be cupped and deformed (tung), bleached (lettuce), flaccid and blue green with chlorotic margins (tomato), abscise early (walnut), and eventually become necrotic in the interveinal areas (tung).


Iron is a very important nutrient for plants because it is essential for growth and development, and it also helps plants to face stresses in the environment. Below a plant, roots branch out into the soil in many directions, looking for the nutrients plants need for survival and growth. Iron is also required for photosynthesis and chlorophyll synthesis. The availability of iron in soils dictates the distribution of plant species in natural ecosystems and limits yield and nutritional quality of crops. The primary symptom of iron deficiency is interveinal chlorosis, the development of a yellow leaf with a network of dark green veins. In severe cases, the entire leaf turns yellow or white and the outer edges may scorch and turn brown as the plant cells die.


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Further Readings


"Diagnosing Nutrient Needs of Garlic" by Kent Tyler, Donald May and John Guerard.


https://www.ars.usda.gov/arsuserfiles/20361500/pdf_pubs/P1137.pdf


Brown PH, et al. 2002: Boron in plant biology. Plant Biology, 4:205–223.

Cakmak I. and Römheld V. 1997: Boron deficiency-induced impairments of cellular functions in plants. Plant Soil, 193:71–83.


Dear BS and Weir RG. 2004: Boron deficiency in pastures and field crops. New South Wales Department of Agriculture AgFacts, P1.AC.1, 2nd Ed.

Marschner P. 2012: Marschner’s Mineral Nutrition of Higher Plants, 3rd Ed. Academic Press.


Eaton, F.M. and L.V. Wilcox. 1939. The behavior of boron in soils. U.S. Dept. Agr. Tech. Bul. 969. Francois, L.E. 1984. Effect of excess boron on tomato yield, fruit size, and vegetative growth.


Francois, L.E. 1986. Effect of excess boron on broccoli, cauliflower, and radish. J. Amer. Soc. Hort. Sci. 111:494-498.


Francois, L.E. 1988. Yield and quality responses of celery and crisphead lettuce to excess boron. J. Amer. Soc. Hort. Sci. 113:538-542.


Francois, L.E. 1989. Boron tolerance of snapbean and cowpea. J. Amer. Soc. Hort. Sci. 114:615– 619. Francois, L.E. and


R.A. Clark. 1979. Boron tolerance of twenty-five ornamental shrub species. J. Amer. Soc. Hort. Sci. 104:319-322. Hatcher,


J.T. and C.A. Bower. 1958. Equilibria and dynamics of boron adsorption by soils. Soil Sci. 85:319-329. Hatcher, J.T., G.Y.


Blair, and C.A. Bower. 1959. Response of beans to dissolved and adsorbed boron. Soil Sci. 88:98-100. John, M. K., H.H.


Chuah, and J.H. Neufeld. 1975. Application of improved azomethine-H method to the determination of boron in soils and plants.







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