Starving For Sulfur

What protective mineral fell free from the skies for many decades until legislation shut down supply? Ironically, this “pollutant” counters toxicity in humans and animals and helps to neutralise the negatives associated with excess nitrates in the food chain and environment. This pungent nutrient is also one of the best ways you can protect your pets from fleas! This often-neglected nutrient is sulfur and it is a keystone tool in biological farming.

Sulfur is one of three nutrients that are cycled between the soil, plant matter and the atmosphere. The carbon, nitrogen and sulfur cycles are all dependent upon specialist bacteria and if these creatures are compromised, the recycling potential is reduced and farmers are forced to increase inputs to compensate for the shortfall.

The supply of sulfur to the plant is biologically determined in another way. Sulfate sulfur is a negatively charged compound (anion) that is stored in the soil through attachment to the positively charged humus colloid. Humus is the sulfur storehouse and as we have depleted our humus reserves (down 70% in the last hundred years) then we have created sulfur shortages in the soil that have impacted plant health. There is another factor that has magnified deficiencies. Sulfur was supplied free with precipitation for many decades as sulfur dioxide spewed freely from industrial smokestacks and fell back to earth as acid rain. However, the resulting acidity of waterways and death of forests, eventually led to legislation banning sulfur emissions and farmers soon discovered a new soil deficiency.

Identifying a Deficiency

Sulfur deficiency in plants can look a lot like a nitrogen shortage, with an overall paling and stunting effect. However, this generalised chlorosis usually happens in the young leaves, while evidence of a nitrogen shortage first appears on the older leaves. There are also a number of species-specific signs of a shortage including poor nodulation on legumes, fruits that do not fully mature and spotting on the leaves of potatoes.

Sulfur deficiency in the soil can be characterised by a tightness linked to accumulation of excess sodium or magnesium. Gypsum (calcium sulphate) is often called “the clay breaker” because it can serve to open up these tight heavy soils. Gypsum has been used for this purpose since 1776. The sulphate ionises from the calcium and can create magnesium sulphate or sodium sulphate, both of which can readily leach from the topsoil and thereby improve gas exchange in the root zone.

There are times, however, when gypsum can prove counterproductive. Large applications of gypsum in acid soils can actually be quite destructive as it can lead to the formation of sulfuric acid and associated soil-life damage.

Protein vs Poison

Sulfur is intimately linked to nitrogen in that both minerals are protein building blocks. Two of the essential amino acids, cysteine and methionine, are sulfur-dependent. These are important nutrients in both animal and human nutrition as they are critical for detoxification (boosting protection in an increasingly toxic world).

Sulfur is also required for the conversion of nitrate nitrogen into protein within the plant leaf. The plant requires sulfur and molybdenum to produce the nitrate reductase enzyme. In the absence of this enzyme, nitrates accumulate within the plant, calling in insects (to perform their garbage collecting role) and reducing the oxygen carrying capacity of the blood of those animals and humans unfortunate enough to consume this toxic food. Multiple studies have linked nitrates to cancer over the past two decades. Nobel prize winner, Dr Otto Warburg, identified anaerobism as the root cause of cancer, and nitrates are a key cause of anaerobism. A small investment in sulfur can reduce the need for chemical intervention because excess nitrates are the single most potent driver of pest pressure.

Other Roles of Sulfur

Sulfur also aids in the translocation of sugars and starches down to the roots. This is why it is considered such a critical nutrient in root crops. Gypsum is often side dressed in crops like peanuts and potatoes to stimulate this translocation. If brix levels do not rise during the day it can be due to a sulfur deficiency. Excess nitrates, with their inevitable nutrient dilution factor, may be accumulating in the leaf due to a lack of sulfur. The other likely cause of brix levels remaining static throughout the day is a boron deficiency, as this mineral opens the trapdoor, which allows the nightly movement of sugars from the chloroplasts in the leaf down to the roots. Sulfur is also required for the formation of chlorophyll itself.

Sulfur is a component of the oil that gives the distinctive smell to onions and garlic and hence these crops are particularly responsive to this mineral. The impressive protective qualities of these crops is partly linked to their high sulfur content.

Canola oil also has a substantial sulfur component and this crop also responds well to sulphate-based fertilisers. However, while garlic and onions are invaluable defence foods, canola produces a junk food oil that should be avoided whenever possible.

Many sulfur compounds form part of the plant’s natural defence system. It is now understood that plants, like animals and humans, have their own immune system and the informed awareness and potential manipulation of this system may well be the future of sustainable pest management. Compounds like glutathione, crucifer phytoalexins and glucosinolates are based upon sulfur and neglect of this mineral will result in reduced plant protection and increased chemical intervention.

Sulfur-based fungicides were the major method of pathogen management in agriculture from 1802 until the late 1970’s and they are still widely used. In 2004, Richard Cooper and Jane Williams, in a paper called “Elemental sulfur as an induced anti-fungal substance in plant defence”, showed that it is not just sulfur compounds that form part of the plant armoury. They found that elemental sulfur itself is also used as a defence chemical to help the plant fight its own battles.

Sulfur in Animal and Human Nutrition

Sulfur is also required to build animal protein. The two sulfur-based amino acids, cysteine and methionine, are critical for the two-stage detoxification system. Both animals and humans have a greater need for a fully-functioning detox system than at any other point in history.

Sulfur is also important for collagen synthesis, which relates to skin health in humans and skin, hair and hooves in animals.

The B vitamins, biotin and thiamine, are manufactured using sulfur, as is the hormone, insulin.

Sulfur is also essential for both internal and external parasite management in both livestock and pets. One of the best techniques to control fleas and ticks in dogs is to include elemental sulfur in their feed. The common rate is half a teaspoon of yellow sulfur every three days for a small dog and a full teaspoon for large dogs. An elderly NTS customer shared another remedy, which has always worked with her pets. She has always fed the dogs a tablespoon of coconut oil and an egg on a daily basis. This serves as a nutritious snack while also keeping her pets flea-free over the past 50 years. Eggs are a sulfur-rich food and coconut oil has anti parasitic qualities.

Sources of Sulfur

Sulfur is largely absorbed in the sulphate (SO₄) form through the roots, but small amounts can also be uptaken as sulfur dioxide gas via the stomates (breathing pores on the underside of the leaf). If a soil is sulfur deficient it can be very productive to include sulphates in the planting blend or via liquid injection. A US study in Arkansas reported a yield increase of almost 200% following the application of just 5 kg per hectare of sulphates in the form of potassium sulphate applied directly into the root zone. However, we normally like to see 25 kg of sulphate sulfur included in any program where the soil test reveals a sulfur deficiency.

Elemental sulfur, in granular form, can also be valuable in some contexts. It is extremely acidifying so that it can be used to lower the root zone pH in alkaline soils. Mineral uptake is pH-dependent so the uptake of several minerals is compromised in high pH soils. A few kg of granular sulfur in the planting blend can lower the pH and increase nutrient availability. The use of elemental sulfur can offer other benefits but it should be applied before planting to ensure availability for plant growth.

A bacterium called Thiobacillus is largely responsible for the conversion of elemental sulfur into the sulphate form. This can take weeks to months depending upon moisture, soil fertility and aeration. These creatures need the same range of minerals as your crop so the better your soil fertility the more suited your soil to the elemental option. A fertile soil will have abundant Thiobacillus, as it will contain the nutrients and the all-important oxygen needed to fuel their activity. By contrast, elemental sulfur is not suited to a closed, high magnesium soil, lacking oxygen.

Productive application rates for granular elemental sulfur involve rates of just 5 kg in the planting blend and up to 40 kg, broadcast several weeks before planting. It is a good idea to think of elemental sulfur like rock phosphate. In both cases the natural, insoluble form can serve to stimulate the soil organisms responsible for solubilising sulfur and phosphate and this can offer secondary benefits in terms of the improved, ongoing recycling of these two minerals.

Sulphate-based fertilisers like ammonium sulphate, magnesium sulphate and potassium sulphate offer a plant available form of sulfur, and gypsum is also a good source (if calcium is also required). Composts can contain good levels of this mineral and fly ash products can be an inexpensive supply (check the heavy metal content of these products before use, as heavy metals will remain long after the sulphates have leached).

There is also a relatively new tool on the market to deliver sulfur to the root zone. Gyp-Life™ is a Micronised Mineral Suspension (MMS) product from NTS that features a micronised liquefied powder that can be fertigated or liquid injected directly beside the roots. Sulfur can be supplied to the plant while also improving soil structure immediately around the roots.

Contact NTS on +61 7 5472 9900 or sales@nutri-tech.com.au for information about our sulfur products.