Garlic Plants Need Sulfur
Updated: Mar 3
Question: Do my Garlic Plants Really Need Sulfur?
Answer: Sulfur (S) is one of the 17 elements essential for all plant growth. Sulfur is the fourth most important element in plant growth after nitrogen (N), phosphorus (P), and potassium (K) in terms of the amount required. Sulfur is a very important component of plant metabolism and is required to improve the overall growth and well-being of plants. The deficiency of sulfur leads to stunted growth of plants and ultimately loss of yield. Sulfur supports several different plant functions, including the formation of enzymes, the creation of new proteins in plants, aiding in photosynthesis and directly affecting growth and energy. Sulfur also helps plants' resistance to disease, aids in bulb growth, and sulfur compounds are directly related to garlic's unique healing benefits and flavors. Sulfur is a structural component of protein bonds, vitamins, and amino acids. Garlic plants absorb sulfur through their root systems in the SO₄²⁻ form. This means that all elemental sulfur, including sulfur in compost and manure, must be converted to SO₄²⁻ in order to be utilized by garlic and other plants.
Sulfate-Sulfur is the only form of sulfur the plant can utilize.
Elemental sulfur is dependent upon time, temperature and moisture to be available to the plant.
Sulfate-Sulfur will not acidify the soil.
Question: Why are the Leaves of our Garlic Plants Turning Yellow?
Answer: Some garlic growers may notice that the leaves of their maturing garlic plants are turning yellow. The initial thought is that the yellowing leaves are a sign of a nitrogen deficiency. But after treating the area around the garlic plants with nitrogen, the yellowing appears to get even worse. This yellowing of the leaves is likely a sign of a sulfur deficiency.
Sulfur plays an important role in the production of chlorophyll and photosynthesis. Garlic plants use the process of photosynthesis to transform sunlight, oxygen, water, and carbon dioxide into oxygen, and simple sugars that the plants use as fuel. Sulfur, calcium, and magnesium make up a group called "secondary nutrients," which means that the quantity of each is vital to the life of a plant. A garlic crop’s need for sulfur is closely associated with nitrogen. Both sulfur and nitrogen are components of protein and are involved in chlorophyll formation. Garlic plants are heavy feeders and have a fairly high nitrogen need. They typically have a high sulfur need as well. Sulfate-Sulfur is the only form of sulfur the plant can utilize.
What is Sulfur? Sulfur or sulphur (Sulfur is used in American English, Sulphur is used in British English) is a pale yellow material that is tasteless, and odorless. On the earth's crust, it can be found as the pure element (S) or as sulfide and sulfate minerals. Sulfur is an essential element for life and is found in two amino acids, Cysteine and Methionine. Sulfur is the chemical element in the periodic table that has the symbol S and atomic number 16 (Sulfur is the 16th most abundant element on Earth's crust). Oxygen, Silicon, Aluminium, Iron, Calcium, Sodium, Magnesium and Potassium are the top 8.
Sulfur is considered the 4th Major Nutrient for Plants, following Nitrogen (N), Phosphorus (P) and Potassium (K). It 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 .
How Many Different Forms of Sulfur Are There?
Chemicals have unique names. Sulfate (Sulphate), sulfite (Sulphite), and sulfur (Sulphur) are three chemicals with different chemical and physical properties. For someone who is not familiar with chemistry, these names sound somewhat the same, but there are differences between sulfur, sulfate, and sulfite?
What is Elemental Sulfur?
Sulfur is a non-metallic element. Sulfur is present in numerous compounds and in various forms which is why it is called an allotropic element. In pure form, sulfur can have many physical forms. The most common is a yellow solid or powder.
What is Sulfate?
Sulfate is an oxy-anion of Sulfur (An oxy-anion is oxygen-containing negative ion). Sulfuric acid consists of two H+ ions and one sulfate ion.
What is Sulfite?
Sulfite is another oxy-anion of sulfur. The difference between sulfate and sulfite lies in the number of atoms present in the ion. Sulfite has three oxygen atoms doubly bonded to the central Sulfur atom. Sulfites are chemicals that are in some foods, either naturally or as additives.
What Form of Sulfur is Used by Plants?
Sulfate-Sulfur is the only form of sulfur the plant can utilize right away. Elemental sulfur needs more time, specific temperatures and moisture to be available to plants. Oxidation is more rapid in warm, moist soils with high organic matter. Oxidation reactions of elemental sulfur are also faster in alkaline soils than in acidic soils.
The majority of sulfur in most soils is contained in organic matter. Sulfate-sulfur, like most anions, is somewhat mobile in soils and therefore subject to leaching. Soil conditions where sulfate-sulfur is most likely to be deficient are low organic matter levels, coarse (sandy) texture with good drainage, and areas that receive significant rainfall. Manure, if available, is an excellent source of sulfur, as well as many other important nutrients. Most livestock manure, including cow and horse manure, contains approximately 0.25% sulfur. Sulfur content is greater, in poultry manure (0.50%).
Sulfate-Sulfur vs Elemental Sulfur Availability in Plants
What is the Role of Sulfur in Garlic Plants and Bulb Growth?
Sulfur not only helps to increase crop yields and improves plant quality, it has the potential to help increase the uptake of nitrogen, phosphorousthe and potassium. Sulfur, in the right form, is essential for nitrogen-fixing and necessary in the formation of chlorophyll. Mo,st sulfur uptake occurs in late season during bulb growth. Garlic plants use sulfur in the processes of producing proteins, amino acids, enzymes, and vitamins. Garlic's unique flavor is due partly to the presence of Diallyl Disulfide (DADS or 4,5-dithia-1,7-octadiene) which is an organosulfur compound found in Allium plants. Plants with a high sulfur content may have a greater tolerance to pest and disease attacks.
Can you add too much sulfur to the soil?
Excessive applications of sulfur most often result in a decline in soil pH and an increase of the problems that occur with the pH decrease. Unfortunately, sulfur uptake is reduced as the pH of the soil decreases.
Strategies to Supplement Sulfur in Your Garden.
A soil test is the most important starting point when determining how much if any sulfur your garden soil will need. A soil-testing laboratory in the midwest, AGVise (www.AGvise.com) can determine the levels of sulfur in your soil, and help you determine how much you will need to add, based on what crop of crops you are growing. Soil testing of sulfur is usually a measure of sulfate-sulfur. Coarse textured soils may need sulfur, but finer textured soils can also be deficient. Heavy-feeding crops such as garlic and onions take up and remove more sulfur from the soil as compared to most grain crops. The best place to start is a soil test, then speak with your fertilizer retailer or agronomist. What source of sulfur is right for you? Selecting the right source of sulfur is critical to ensure enough sulfate-sulfur is present in the soil at key uptake periods. There are several sulfur fertilizer sources available for purchase. Most soluble sulfur fertilizer contains sulfate, but others contain bisulfites, thiosulfates, and polysulfides. The most common insoluble sulfur fertilizer is elemental sulfur, which must be oxidized to sulfate before plants can use it. Keep in mind that Sulfur is included in fertilizer through a range of sources that include:
Gypsum or Calcium Sulfate
Sulfur is contained in organic matter such as manure and compost, and if you regularly apply organic matter such as compost or manure to your garden, keep in mind that organic sulfur must be mineralized to the inorganic sulfate anion before it can be taken up by crops. The decomposition of organic materials and the resulting sulfur release varies greatly, as this is a biological process and is affected by temperature, moisture, aeration and particle size. This process also produces some acidity in the soil. Remember that the lower the pH number, the more acidic it's considered. Garlic grows best in soils with a pH between 6-7.
Sulfate fertilizer sources like ammonium, potassium and calcium sulfate will provide readily available sulfate to a garlic crop. The drawback of these materials is that this form of sulfate can leach through the soil profile quickly after application. While it is possible to leach sulfate, research in Minnesota has demonstrated that sulfate can carry over in medium- to fine-textured soils and be in the soil profile that fall and even the year following application. Fall application of sulfate can provide available sulfur to the crop the following year.
When Elemental sulfur is applied to the soil, throughout the growing season, soil microbes convert the elemental sulfur into sulfate-sulfur for season-long feeding. Size matters! The smaller the size of elemental sulfur particles, the easier it is for the microbial population to oxidize it into sulfate-sulfur
When Sulfate-Sulfur-based fertilizer is applied, it supplies both S₄²⁻ and S⁰ in the same granule. When fertilizers are applied to the soil, the sulfate-sulfur is already in the proper form to feed the plant. Fertilizer granules rapidly dissolve and move sulfate-sulfur into the root zone for early-season development. This ensures season-long sulfur availability.
What Are the Best Sulfur Fertilizers for Organic Crops?
Synthetic fertilizers such as ammonium sulfate (AMS), potassium sulfate, and ammonium thiosulfate are not considered organic. What sulfur fertilizers are best for use in organic crop production? Here is a short list of sulfur fertilizers available for use in organic systems (Organic Materials Review Institute (OMRI)).
Bentonite sulfur fertilizers (elemental sulfur).
You won’t find a more economical, higher analysis, season-long source of sulfur for agricultural use. Its two primary ingredients are organic: elemental sulfur and bentonite clay. In most cases, the only additional requirement necessary to achieve OMRI certification is the use of an organic dust-suppressanutrientsnt. Bentonite sulfur provides season-long, slow release sulfur nutrient to the crop. Generally 30%-40% is converted to sulfate over the growing season. Some products are made with a slow-release mechanism which can minimize the risk of leaching. Bentonite sulfur fertilizers can be used for soil amendment programs to lower pH. Elemental sulfur, the concentrated form of sulfur, must be oxidized to the sulfate before plants use it.
Gypsum (Calcium sulfate).
Gypsum has been used to improve soil quality for a long time. It contains approximately 17% sulfur and is a readily-available sulfate. Gypsum is commonly used as sulfur sources, only where soils or cropping call for it. Gypsum is immediately plant available, and is an affordable sulfur source and source of calcium. It can be used as a soil amendment to increase organic content as well.
Manure is an excellent source of sulfur, as well as many other important nutrients. “Most livestock manure contains approximately 0.25% to 0.30% sulfur. Sulfur content is greater, however, in poultry manure (0.50%)” – Sulfur Fertility for Crop Production.
Organic Matter such as aged compost is a good source of sulfur. In order for sulfur to mineralize and become available for plants, a number of microbial processes need to occur.
Sulfur deficiency results in poor quality and yield of crops. Begin with a soil test to determine if your soil requires additional sulfur. Sulfur exists in many different forms in nature, and plants can absorb sulfur only through their root systems in the SO₄²⁻ form, also known as sulfur-sulfate. All soil elemental sulfur must be converted to SO₄²⁻ in order to be utilized by plants. This means that elemental sulfur, S⁰, is totally unavailable to plants. Elemental S is inert and water-insoluble. When elemental sulfur, S⁰, is added to the soil, microbes, moisture and heat convert S⁰ to a form the plants can use, namely sulfur-sulfate, SO₄²⁻. There are many sources of sulfur found in the soil. Organic matter contains up to 95% of the total sulfur content in soils and the decomposition of organic matter results in the mineralization of organic sulfur into the SO42−, which will be available to plants. Microbial activity is reduced by cold and excessively wet or dry conditions. There are more than 22 different sulfur-containing fertilizers are available commercially which is immediately available for plant uptake. Some chemical fertilizers contain a considerable amount of sulfur along with nitrogen, potassium, and phosphorus. The timing and type of sulfur application influence the presence of sulfur in the soil and the availability of the plant. Crop yield can be sustainably improved by adding the right type of sulfur to the soil.
Additional Reading and Resources
Influence of sulfur on growth and yield of garlic (Allium sativum L.). Author(s): SB Babaleshwar, Shilpa R Koppad, KK Math and R Dharmatti. Abstract: The experiment was conducted at Main Agricultural Research Station, UAS, Dharwad during rabi season of 2014-15 to study the effect of sulfur on the productivity of garlic. Read more here:
Mr. Jere Folgert is the owner of GroEat Garlic Farm in Bozeman, Montana. GroEat Farm is a small, sustainable family farm located inthe shadows of the Gallatin Mountain Range. The hardneck varieties grown on their farm flourish, due to the combination of the very cold winters, heavy snowpack, moist spring, temperate summers, and the nutrient-rich and dynamic alluvial soils, washed down from the Gallatin Mountain Range.
Vauclare P, Kopriva S, Fell D, Suter M, Sticher L, von Ballmoos P, Krähenbühl U, Op den Camp R, Brunold C (2002) Flux control of sulphate assimilation in Arabidopsis thaliana: adenosine 5′-phosphosulphate reductase is more susceptible than ATP sulphurylase to negative control by thiols. Plant J 31: 729–740 [PubMed] [Google Scholar]
Sanda S, Leustek T, Theisen MJ, Garavito RM, Benning C (2001) Recombinant Arabidopsis SQD1 converts UDP-glucose and sulfite to the sulfolipid head group precursor UDP-sulfoquinovose in vitro. J Biol Chem 276: 3941–3946 [PubMed] [Google Scholar]
Nocito FF, Pirovano L, Cocucci M, Sacchi GA (2002) Cadmium-induced sulfate uptake in maize roots. Plant Physiol 129: 1872–1879 [PMC free article] [PubMed] [Google Scholar]
Leustek T, Saito K (1999) Sulfate transport and assimilation in plants. Plant Physiol 120: 637–643 [PMC free article] [PubMed] [Google Scholar]
Nakai Y., Maruyama-Nakashita A. Biosynthesis of Sulfur-Containing Small Biomolecules in Plants. Int. J. Mol. Sci. 2020;21:3470. [PMC free article] [PubMed] [Google Scholar]
Maruyama-Nakashita A. Metabolic changes sustain the plant life in low-sulfur environments. Curr. Opin. Plant Biol. 2017;39:144–151. [PubMed] [Google Scholar]
Yoshimoto N., Saito K. S-Alk(en)ylcysteine sulfoxides in the genus Allium: Proposed biosynthesis, chemical conversion, and bioactivities. J. Exp. Bot. 2019;70:4123–4137. [PubMed] [Google Scholar]
Kopriva S., Malagoli M., Takahashi H. Sulfur nutrition: Impacts on plant development, metabolism, and stress responses. J. Exp. Bot. 2019;70:4069–4073. [PubMed] [Google Scholar]
Watanabe M., Hoefgen R. Sulphur systems biology-making sense of omics data. J. Exp. Bot. 2019;70:4155–4170. [PMC free article] [PubMed] [Google Scholar]
Aarabi F., Naake T., Fernie A.R., Hoefgen R. Coordinating Sulfur Pools under Sulfate Deprivation. Trends Plant Sci. 2020;25:1227–1239. [PubMed] [Google Scholar]
Bouranis D.L., Malagoli M., Avice J.C., Bloem E. Advances in Plant Sulfur Research. Plants. 2020;9:256. [Google Scholar]
Camberato, Jim. 2013. Striped Corn – Potential Nutritional Deficiencies. Soil Fertility Update, Agronomy Dept., Purdue Univ.
https://www.agry.purdue.edu/ext/soilfertility/news/Striped_Corn.pdf [Accessed Jan 2023]
Hasanuzzaman M., Bhuyan M.H.M.B., Mahmud J.A., Nahar K., Mohsin S.M., Parvin K., Fujita M. Interaction of sulfur with phytohormones and signaling molecules in conferring abiotic stress tolerance to plants. Plant Signal. Behav.
Capaldi F.R., Gratão P.L., Reis A.R., Lima L.W., Azevedo R.A. Sulfur Metabolism and Stress Defense Responses in Plants. Trop. Plant Biol. 2015;8:60–73. [Google Scholar]
Chan K.X., Phua S.Y., Van Breusegem F. Secondary sulfur metabolism in cellular signalling and oxidative stress responses. J. Exp. Bot. 2019;70:4237–4250. [PubMed] [Google Scholar]
Aarabi F., Kusajima M., Tohge T., Konishi T., Gigolashvili T., Takamune M., Sasazaki Y., Watanabe M., Nakashita H., Fernie A.R., et al. Sulfur deficiency-induced repressor proteins optimize glucosinolate biosynthesis in plants. Sci. Adv. 2016;2:e1601087. [PMC free article] [PubMed] [Google Scholar]
Vauclare, P., Kopriva, S., Fell, D., Suter, M., Sticher, L., Von Ballmoos, P.,et al. (2002). Flux control of sulphate assimilation in Arabidopsis thaliana: adenosine 5′-phosphosulphate reductase is more susceptible than ATP sulphurylase to negative control by thiols. Plant J. 31, 729–740.
Zhang L., Kawaguchi R., Morikawa-Ichinose T., Allahham A., Kim S.-J., Maruyama-Nakashita A. Sulfur Deficiency-Induced Glucosinolate Catabolism Attributed to Two β-Glucosidases, BGLU28 and BGLU30, is Required for Plant Growth Maintenance under Sulfur Deficiency. Plant Cell Physiol.
Tabe, L. M., and Droux, M. (2001). Sulfur assimilation in developing lupin cotyledons could contribute significantly to the accumulation of organic sulfur reserves in the seed. Plant Physiol. 126, 176–187. doi: 10.1104/pp.126.1.176
Fuentes-Lara L.O., Medrano-Macías J., Pérez-Labrada F., Rivas-Martínez E.N., García-Enciso E.L., González-Morales S., Juárez-Maldonado A., Rincón-Sánchez F., Benavides-Mendoza A. From Elemental Sulfur to Hydrogen Sulfide in Agricultural Soils and Plants. Molecules. 2019;24:2282. [Google Scholar]
Smith, I. K. (1980). Regulation of sulfate assimilation in tobacco cells: effect of nitrogen and sulfur nutrition on sulfate permease and O-acetylserine sulfhydrylase. Plant Physiol. 66, 877–883. doi: 10.1104/pp.66.5.877