Sulphur has been recognized as one of the many elements required for plant growth for nearly 130 years. Interest in sulphur as a plant nutrient has increased greatly in the past few years, partly because reports of sulphur deficiency throughout the world are becoming more frequent and extensive. The main reasons for greater occurrence of sulphur deficiencies are:
- Increased use of high analysis, essentially sulphurfree fertilizers.
- Decreased use of sulphur as a fungicide and insecticide.
- Increased crop yields which require larger amounts of all of the essential plant nutrients.
- Increased consumption of low sulphur fuels and increased emphasis on control of air pollution.
- Increased ability to identify soils low in sulphur.
Sulphur’s role in the plant.
Sulphur is required by the plant for:
- The synthesis of the amino acids, cystine, cysteine, methionine and hence for protein elaboration.
- The activation of certain proteolytic enzymes such as the papainases.
- The synthesis of certain vitamins (biotin and thiamin or vitamin B1 ), glutathione and of coenzyme A.
- The formation of the glucoside oils found in onions, garlic and cruciferous plants.
- The formation of certain disulphide linkages which are associated with the structural characteristics of protoplasm. The concentration of phydril. (-SH) groups in plant tissues has also been shown to be related to increased cold resistance in some species. Sulphur was recently shown to be present in the nitrogenase enzyme system which is involved in the fixation of nitrogen by micro-organisms. In certain situations free-living nitrogen-fixing organisms in the soil and the nodule bacteria in legumes will make significant contributions to the nitrogen supply soils.
The link between Sulphur & Nitrogen
Nitrogen and sulphur requirements are closely linked because both are required for protein synthesis.Plant protein contains about 1% S and 17% N. The need for sulphur fertilization often depends upon the supply of N and other nutrients and fertilization at high rates with these elements may induce a sulphur deficiency.
Why is Sulphur important?
Greening of Turf
In the absence of sulphur, turfgrass exhibits a chlorosis that frequently occurs as an intense yellow color. In mild cases one may think of nitrogen deficiency or even iron deficiency.
On the positive side, we find that sulphur enhances color, density and growth. Sulphur helps nitrogen (N) to be used efficiently. There seems to be a direct relationship with nitrogen. The turfgrass fertilized with the higher quantities of nitrogen show increased response to sulphur. It has been reported that when 5.45kg of nitrogen are used, there is a requirement for 3.63kg of potassium oxide and 1.57kg of sulphur.
The net effects of adequate sulphur in combination with N, P and K are several:
- Better decomposition of residues (thatch).
- Stimulation of soil microorganisms.
- Improved color, density and composition of turfgrass.
- Greater drought tolerance.
- Improved winter hardiness.
Sulphur reduces disease In turf.
Well-documented studies by Goss, Gould and others reveal some very convincing reasons for applying sulphur along with nitrogen, phosphorus and potassium. Adequate sulphur reduced Fusarium patch in turfgrass by 86%.
This property of controlling disease really should cause no great surprise because we have known this about sulphur for a long time. The surprising thing is that so many of us have forgotten it or have not put the knowledge to use.
Another turfgrass disease that has been checked and controlled to a large degree with sulphur is Ophiobolus patch.
When Merion Kentucky Bluegrass is short of sulphur, it is much more susceptible to powdery mildew. Dollarspot fungus in warm-season grasses in Florida was reduced by the use of sulphur in fertilizers. This may be a bit hard for many to believe, but data from the Pacific N.W. shows that adequate sulphur prevented Poa annua from infesting bentgrass turf. At the same time the blue-green algae was reduced significantly.
Perhaps some of the advantages found in using adequate sulphur come from the fact that turf is rendered more vigorous, an obvious sign of healthier grass. Healthy turf resists injuries and recovers faster when injury occurs.