NPS [CAS?]-4S is a high-analysis compound carrying slightly more nitrogen than phosphorus, with a modest sulfur component and no potassium. At 48 % total declared nutrient it is concentrated, and its 4 % sulfur figure places it in a distinctly different category from the 13 % sulfur grades: this is a maintenance sulfur dose intended to keep pace with crop removal, not a corrective dose intended to fix an established deficiency. That distinction determines where the grade fits and where it does not.
Substance identity
| Field | Value |
|---|---|
| Product type | Formulation — no single CAS number |
| Grade | [CAS?]-4S (N — P₂O₅ — K₂O — S) |
| Nutrients per tonne | 230 kg N · 210 kg P₂O₅ · 0 kg K₂O · 40 kg S |
| Total declared nutrient | 48 % |
| Sulfur expressed as SO₃ | 4 % S = 10 % SO₃ |
| Typical constituents | ammonium phosphates with a nitrogen carrier and a sulfate source |
No single CAS number exists for this product. It is a formulation, not a substance. Each constituent — ammonium phosphate, the nitrogen carrier, the sulfate source — holds its own CAS number and is declared separately on the safety data sheet. A single CAS presented for a compound NPK grade is a misuse of the registry.
Specification
Typical commercial declaration — confirm on certificate of analysis:
| Parameter | Typical |
|---|---|
| Total nitrogen (N) | 23 % |
| P₂O₅, total | 21 % |
| K₂O | 0 % |
| Sulfur (S) | 4 % |
| Sulfur form | confirm on specification |
| Moisture | ≤ 1.5 – 2.5 % |
| Particle size | ≥ 90 % within 2 – 4 mm |
| Appearance | granular |
Properties
-
N : P₂O₅ ratio of about 1.1 : 1 — marginally nitrogen-leaning. Against a balanced [CAS?] applied at the same rate, this grade delivers 15 % more nitrogen and 5 % more phosphorus.
-
4 % sulfur is a maintenance rate, not a corrective one. At 4 % S, a 200 kg/ha application supplies 8 kg S/ha. That is in the region of what a moderate cereal crop removes, so the grade holds the soil sulfur balance roughly steady. It is not sufficient to correct an established sulfur deficiency, and it is well short of what a high-demand brassica or oilseed crop requires. For those situations a 13 % S grade or a separate sulfur application is needed. Stating this clearly matters, because “contains sulfur” is otherwise read as “sulfur is handled”.
- N : S ratio of about 5.8 : 1 in the product — reasonably close to the proportional uptake ratio of many cereals, which is consistent with a maintenance role.
- 48 % total declared nutrient — high concentration, favourable freight and handling economics per unit of nutrient delivered.
- Sulfur and nitrogen forms are not visible in the grade and should be requested.
Applications
-
Basal application in cereal systems — wheat, maize, barley, rice, sorghum — where nitrogen demand is high, phosphorus status is medium, potassium is adequate or supplied separately, and sulfur needs maintaining rather than correcting.
-
The nitrogen-leaning ratio in practice. Most annual crops remove nitrogen at several times their phosphorus removal, so a grade near 1 : 1 still leaves a substantial nitrogen gap to be closed by topdressing. A ratio slightly above 1 : 1 narrows that gap marginally and lets a larger share of the season’s nitrogen be placed at sowing, which suits situations where field access later in the season is uncertain or where the number of passes must be reduced. It does not eliminate the need for topdress nitrogen in any high-yielding cereal program.
- Soils with sufficient but not abundant sulfur, where the aim is to prevent deficiency developing rather than to reverse one.
- Where a 13 % S grade should be chosen instead: canola, rapeseed, mustard, sunflower and brassica vegetables; any soil with a diagnosed sulfur deficiency; light-textured, low-organic-matter or high-rainfall soils where sulfate leaching is significant; and any situation where sulfur deficiency symptoms — chlorosis on the youngest leaves — have already been observed.
- The 0 % K decision applies as elsewhere: justify from soil test and crop removal, supply K separately where required, and do not run zero-K compounds indefinitely on soils of moderate or low potassium status.
Handling and storage
Dry, covered, ventilated storage; bagged on pallets, clear of floors and walls; humidity control, as multi-salt compounds have a lower critical relative humidity than their individual components. Where the product contains urea, moisture sensitivity is higher again. Limit stack height to avoid consolidation caking. Segregate from lime, basic slag, calcium cyanamide and other alkaline materials — contact liberates ammonia and reduces phosphate availability. Keep away from heat and from moisture ingress. Minimize transfer points to limit fines and preserve spread pattern.
Notes
-
No single CAS number; constituents listed individually on the SDS.
-
4 % S = 10 % SO₃. Confirm the declaration basis before comparing against any other sulfur-bearing grade.
- Request the forms of nitrogen and sulfur; the grade notation carries only totals.
- Conversion: 21 % P₂O₅ = 9.2 % elemental P.