• Jere Folgert

GARLIC NEEDS: Sulphur, Boron, Zink and Copper

Updated: Sep 30

There are only few studies on the effects of micronutrient effects on garlic. Most of the researches on nutrition of garlic limit the recommendation for major nutrients like N, P, and K, but micro-nutrients also play a vital role in deciding the growth and development of garlic plants. Meanwhile, the minerals BORON (B), COPPER (Cu). ZINK (Zn) and IRON (Fe) dynamically take place in several enzymatic and biochemical events for better yield and quality of garlic. A similar response of micro mineral nutrition was reported to be effectively improved yield and quality of garlic. 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.

A study published by the USDA, provided explored 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.

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Boron (B) is a micronutrient critical to the growth and health of all crops. 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.

Major Functions of Boron in Plants. 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.

Plant Analysis for Boron. 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.

Boron Deficiency Symptoms. 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

Soil Factors Affecting Boron Deficiency in Plants. 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 Affecting Boron Deficiency. 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 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.

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).

Sufficient Boron for Better Root Uptake of Phosphorus and Potassium. Studies show that adequate B 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.

Further Readings

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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