Animals need to consume methionine in their diet as they cannot manufacture it themselves; methionine is essential for dairy cattle in particular.

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1 The Importance Of Sulphur As A Plant Nutrient Sulphur is an important nutrient for optimal plant growth: it is one of the key macroelements essential for plant growth. Sulphur is taken up from the soil solution by the plant in the sulphate form (SO 4 2- ). In the plant sulphur is a component of methionine, cysteine and cystine, three of the 21 amino acids which are the essential building blocks of proteins. Animals need to consume methionine in their diet as they cannot manufacture it themselves; methionine is essential for dairy cattle in particular. Sulphur is also a component of key enzymes and vitamins in the plant and is necessary for the formation of chlorophyll. In legumes sulphur is necessary for the efficient fixation of nitrogen by the plant. This makes sulphur of fundamental importance in the establishment and maintenance of legume-based improved pastures. It is also essential for flowering and seed set in canola. Plants which are deficient in sulphur show a pale green colouration of younger leaves first as sulphur is not very mobile in the plant. In severe cases of sulphur deficiency the entire plant can be stunted and pale green. Affected plants may be thin-stemmed and spindly; brassica and canola crops may develop a reddish colouration on the underside of leaves and on stems, and flowers may be pale to greyish in colour. Sulphur has become more important as a key plant nutrient in recent times due to a number of factors: Increased use of high analysis fertilisers such as monoammonium phosphate (MAP) and diammonium phosphate (DAP). These products contain much less sulphur that the traditionally used single superphosphate (SSP); Decreased sulphur addition to the soil from atmospheric sources as industrial pollution has been reduced; Introduction of higher yielding crop varieties which remove more sulphur from the soil in harvested commodities.

2 the sulphur cycle Sulphur is present in various forms in the environment. Up to 95% of the total sulphur in the soil is associated with organic matter. Other sources of sulphur in soils are animal manure, irrigation water and, close to the coast or industrial areas, the atmosphere, where sulphurous gases such as sulphur dioxide and sulphur trioxide are dissolved in rainwater and washed into soil. The availability of sulphur from industrial emissions is relatively low in countries like Australia with legislation aimed at reducing industrial pollution. In the soil sulphur is present as organic sulphur compounds, sulphides (S - ), elemental sulphur (S 0 ), and sulphate (SO 4 2- ). Plants cannot absorb organic or elemental sulphur. For plants to be able to utilise sulphur from the soil it must be in the sulphate form. Organic sulphur and elemental sulphur are converted to the sulphate form in the soil. Sulphur can be removed from soil through uptake by plants, leaching through and out of the root zone by rainfall or irrigation, and by volatilisation. Sulphur can be transformed from one form to another in the soil through various biological and physical processes. This movement in and out of the soil between different chemical forms in the soil is known as the sulphur cycle. The sulphur cycle can be represented as shown below:

3 How sulphur is lost from the soil The main ways sulphur is removed from pastures and soils is through leaching out of the root zone of plants and by ingestion of pasture by grazing animals. Leaching is the process whereby water, in the form of rainfall, flood waters or irrigation, is flushed through the root zone. This flushing process takes with it dissolved nutrients so that they become unavailable to plants through normal root uptake. Because sulphur in the sulphate form is very soluble it is easily leached out of the root zone under conditions of heavy rainfall or irrigation, and under conditions of moderate rainfall or irrigation in light soils. Studies in New Zealand have shown that 5-40kg S per hectare per year can be lost from grazed pastures through leaching. The advantage of adding elemental sulphur to the soil is that it acts as a slow release source of sulphur to the plant as elemental sulphur is resistant to leaching and is oxidised slowly to sulphate as the plant requires it. Sulphur is also lost from the soil in plant and animal products. The following table provides a guide to the amount of sulphur removed by various crops and by dairy production: CROP & COMMODITY SULPHUR REMOVAL (kg/tonne of product) Barley (grain) 1.1 Cattle live 3.9 Cattle live wt gain 1.5 Canola (grain) 9.8 Cotton (lint and seed) 4.0 Greasy wool 28.5 Hay cereal 1.5 Hay legume 2.0 Hay lucerne 3.2 Maize (grain) 3.8 Milk 0.3 Oats (grain) 1.5 Potato (tuber) 4.5 Sheep live 4.0 Sheep live wt gain 1.7 Sorghum (grain) 2.8 Wheat Prime Hard (grain) 1.64 Wheat Aust. Hard (grain) 1.40 Wheat ASW (grain) 1.35 Wheat Soft (grain) 1.19 Wheat Durum (grain) 1.52 (Australian Soil Fertility Manual, 2004; Appendix 1.)

4 Conversion of elemental sulphur to the sulphate form Plants cannot absorb elemental sulphur. For sulphur to be taken up by plants it must be in the sulphate form (SO 4 2- ). Elemental sulphur is converted to the sulphate form in soil through a process of oxidation by bacteria, mainly Thiobacillus species. The rate of conversion from elemental sulphur to sulphate is influenced by: 1. The particle size of the elemental sulphur source Because the oxidation process is due to bacterial activity, the more surface area the bacteria are able to access the quicker the rate of oxidation will be. The smaller the particle size of the elemental sulphur source, the greater the surface area for a given weight of sulphur, hence the process of oxidation will be quicker for small sized particles of elemental sulphur than larger sized particles. Generally, for elemental sulphur to be a useful source of sulphate, the particle size of the elemental sulphur needs to be less that around 0.3mm (300 microns). The particle size of the elemental-s is the main condition that can be controlled by fertiliser. Large particles, bigger than 500 microns in diameter, are of little value from an agronomic standpoint. The importance of particle size on the oxidation rate of elemental-s is shown in Figure 1. The rate of bacterial metabolism and reproduction is related to temperature: at very low or very high temperatures bacterial multiplication is limited. Oxidation of sulphur to sulphate occurs between 5 o C and 40 o C and is most active between 10 o C and 30 o C; this is generally true of plant growth as well. At normal temperatures, in the presence of moisture, bacterial multiplication is optimal and the rate of conversion of elemental sulphur to sulphate will be optimal. This means that elemental sulphur is converted to plantavailable sulphate at the time when the plant requires it when soil temperatures favour plant growth they also favour the oxidation of elemental sulphur to sulphate. SULPHUR RECOVERED AS SULPHATE (PERCENT) microns microns microns microns microns Figure 1. S particle size and conversion to sulphate with time. Study of the effect of particle size in microns on recovery of sulphate ions over time from 1000ppm of elemental S incubated in soil at room temperature.

5 Conversion of elemental sulphur to the sulphate form 2. Soil moisture and aeration The Thiobacillus bacteria primarily responsible for the oxidation of sulphur are characterised as aerobic, that is they require oxygen to survive and thrive. They also require a moderate amount of moisture. Soils which are below field capacity but not too dry for extended periods are ideal for the growth and reproduction of Thiobacillus spp and allow optimal rates of oxidation. Soils which are waterlogged for extended periods of time become anaerobic and therefore unsuited to the growth of Thiobacillus spp, thus limiting the conversion of elemental sulphur to the sulphate form. 3. Soil ph (acidity) Oxidation of elemental sulphur to sulphate can occur over a wide range of soil ph (between ph 2 and ph 9). As soil acidity decreases and the soil becomes more alkaline the rate of oxidation generally increases. Liming highly acidic soils will generally increase the rate of oxidation. 4. Amount of organic matter present in the soil Organic matter is the main source of sulphur in soils: the higher the level of organic matter in the soil, the higher the rate of oxidation and conversion of elemental sulphur to sulphate. Under conditions favouring oxidation for each 1% of organic matter in the soil approximately 6kg S are released per annum. 5. Microbial population in the soil In soils which have had sulphur applied in their recent history, levels of sulphur oxidising bacteria are likely to be relatively high. In soils with a history of no sulphur addition the bacterial are generally present in the soil, but at low levels. When sulphur is added to soils with no history of sulphur application the populations of oxidising bacteria build up quickly because it is a source of energy.

6 Wengfu SuStain: The product and the manufacturing process Wengfu SuStain is a high analysis pastille product containing 90% elemental sulphur in a matrix of bentonite clay. It is manufactured by adding bentonite to molten sulphur, shaping the resulting liquid mixture into pastilles, and cooling. The bentonite pastilles are designed to swell and disintegrate when they come into contact with moisture, releasing thousands of tiny sulphur particles which are available to be oxidised to the plant available sulphate form by bacteria in the soil. Wengfu SuStain contains a range of different sized elemental sulphur particles. This ensures that some of the sulphur is available for immediate oxidation to the sulphate form, and some remains in the soil to be oxidised over a longer time frame, thus ensuring an ongoing supply of sulphate to the plant. Research work has demonstrated that applications of elemental sulphur can be at least as effective as applications of sulphate provided that the elemental sulphur particles are less that around 300 microns in diameter; extremely fine particles (< 75 microns) can oxidise within 2-3 days under ideal conditions. The majority of sulphur particles in Wengfu SuStain are less than 300 microns in diameter. The breakdown of Wengfu SuStain over an 8 hour period: demonstrates the rapid breakdown of the pastilles and the release of elemental sulphur particles on contact with moisture, exposing the sulphur particles to microbial oxidation to the sulphate form.

7 Combining Wengfu SuStain and Wengfu Pasture King The combination of Wengfu SuStain and Wengfu Pasture King gives the ideal balance of immediately available sulphate and sustained release elemental sulphur. Wengfu Pasture King is a combination of 15.7% phosphorus, combined with 4.6% sulphate. The high concentration of phosphate gives economies of transport and storage, and the sulphate is immediately available for plant uptake. The high loading of sulphur (90%) in Wengfu SuStain delivers elemental sulphur in a range of particle sizes so that a proportion is immediately available to the plant and a proportion is slowly oxidised over time to meet the longer term requirements of the plant as it is actively growing. Custom blends of Wengfu Pasture King and Wengfu SuStain can be made to meet the specific nutrient needs of pastures based on soil and plant analyses.