NPS [CAS?]-13S adds a declared, guaranteed sulfur component to the phosphorus-leaning [CAS?] base. The distinction from an ordinary NP grade is not cosmetic: sulfur here is a specified nutrient with a number attached to it, subject to the same declaration and testing as N and P, rather than an incidental by-product of the manufacturing route that may or may not be present in the next lot. At 13 % S the sulfur loading is substantial — roughly two-thirds of the phosphate figure — and this grade is chosen specifically where sulfur is agronomically limiting.
Substance identity
| Field | Value |
|---|---|
| Product type | Formulation — no single CAS number |
| Grade | [CAS?]-13S (N — P₂O₅ — K₂O — S) |
| Nutrients per tonne | 160 kg N · 200 kg P₂O₅ · 0 kg K₂O · 130 kg S |
| Sulfur expressed as SO₃ | 13 % S = 32.5 % SO₃ |
| Typical constituents | ammonium phosphate with ammonium sulfate |
No single CAS number. This is a formulation of several substances, each with its own registry identifier, declared separately on the safety data sheet.
Specification
Typical commercial declaration — confirm on certificate of analysis:
| Parameter | Typical |
|---|---|
| Total nitrogen (N) | 16 % |
| P₂O₅, total | 20 % |
| K₂O | 0 % |
| Sulfur (S) | 13 % |
| Sulfur form | sulfate (SO₄²⁻) — confirm; see properties |
| Moisture | ≤ 1.5 – 2.5 % |
| Particle size | ≥ 90 % within 2 – 4 mm |
| Appearance | granular |
Properties
-
Sulfur form is the property that determines whether this product works this season. Sulfur supplied as sulfate is immediately plant-available — it is the ion roots actually take up, and it acts within days. Sulfur supplied as elemental S is not available until soil microorganisms oxidize it to sulfate, a process that depends on soil temperature, moisture, aeration and particle fineness and that can take weeks to months. Both are honestly declared as “13 % S”. They are not agronomically equivalent, and for a crop with an in-season sulfur deficiency the difference is the whole point. Confirm the form before purchase. Grades of this type built from ammonium sulfate carry sulfate sulfur.
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13 % S is a high loading relative to the nitrogen figure — an N : S ratio of about 1.2 : 1 in the product.
- Sulfate is mobile in soil, behaving broadly like nitrate: it leaches on light-textured soils under high rainfall or heavy irrigation. Sulfate sulfur is therefore best applied close to the period of crop demand rather than far in advance on sandy soils.
- Total declared nutrient 49 %, of which more than a quarter is sulfur.
- Nitrogen form should be confirmed as for any compound.
Applications
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Oilseeds and brassicas first. Canola, rapeseed, mustard, sunflower and the brassica vegetables have among the highest sulfur requirements of any field crops, because sulfur is a constituent of the glucosinolates and the sulfur-containing amino acids these crops accumulate. Canola in particular removes sulfur at a rate approaching a fifth of its nitrogen removal, and sulfur deficiency in canola causes flower abortion and pod set failure — a yield loss that no amount of nitrogen will recover.
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Legumes and pulses, where sulfur supports nodulation and the synthesis of sulfur-containing amino acids in the seed.
- Cereals on sulfur-deficient soils. Sulfur deficiency in wheat depresses grain protein quality and baking performance even where total protein looks acceptable, because it is the sulfur-containing storage proteins that are shorted.
- Why sulfur deficiency is now common and was not always. Historically a significant share of crop sulfur arrived as atmospheric deposition from industrial sulfur dioxide emissions. Emission controls have substantially reduced that input across many regions. At the same time, yields have risen — increasing removal — and high-analysis fertilizers have displaced the older low-analysis products that carried incidental sulfur. Sulfur deficiency has consequently emerged on soils that never previously required it, particularly light-textured, low-organic-matter and high-rainfall soils.
- Recognizing it in the field. Sulfur is relatively immobile within the plant, so deficiency shows on the youngest leaves first — the opposite of nitrogen deficiency, which appears on the oldest leaves. The two are otherwise similar enough in appearance that they are routinely confused, and treating a sulfur deficiency with more nitrogen makes matters worse.
- The 0 % K decision applies as for any zero-potassium grade: appropriate where soil K is adequate or K is supplied separately; not appropriate as a permanent program on low-K soils.
Handling and storage
Dry, covered, ventilated storage; bagged on pallets; humidity control, as multi-salt compounds have a lower critical relative humidity than their constituents. Limit stack height. Segregate from lime, basic slag and other alkaline materials — contact with ammonium sulfate-bearing products liberates ammonia. Keep away from heat and moisture. Minimize transfers to limit fines generation.
Notes
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No single CAS number; constituents listed individually on the SDS.
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13 % S = 32.5 % SO₃. Verify the declaration basis before comparing this product against any other sulfur-containing grade.
- Ask for the sulfur form, not just the sulfur percentage. Sulfate and elemental sulfur behave completely differently within a growing season.
- Conversion: 20 % P₂O₅ = 8.7 % elemental P.