Single super phosphate (SSP) is a water-soluble phosphate fertilizer made by reacting finely ground phosphate rock with sulfuric acid. What keeps SSP globally relevant is its three-in-one nutrition: it supplies phosphorus (P) for roots and early growth, plus sulfur (S) and calcium (Ca)—often the “missing” nutrients in many soils. Although higher-analysis phosphate fertilizers exist, SSP remains widely used where sulfur is deficient and as a key raw material in blended and compound fertilizers.
Part of Goway’s comprehensive Phosphates Encyclopedia.
1) Chemical composition & technical specifications (B2B essentials)
1.1 What SSP is made of (chemistry)
SSP is not a single pure compound—it is a mixture, mainly containing:
- Monocalcium phosphate (water-soluble P source): Ca(H2PO4)2·H2O
- Gypsum (sulfur & calcium carrier): CaSO4·2H2O
This MCP + gypsum combination is the reason SSP naturally supplies both phosphorus and sulfur.
1.2 Typical nutrient content (industry ranges)
| Component | Typical range | Why it matters |
|---|---|---|
| P2O5 | 16–22% (available P2O5 ≤ 22%) | Primary phosphate nutrition for roots and early vigor |
| S | 11–12% | Essential for protein synthesis; supports oilseed/cereal quality |
| Ca | 18–21% | Helps improve acidic soils and supports cell wall strength |
| Moisture | Typically controlled (commonly ≤5% for granular trade specs) | Storage stability, flowability, reduced caking |
These ranges align with widely cited nutrient-source references and regulatory/industry definitions for “normal/ordinary” superphosphate.
1.3 Physical form & particle size
- Appearance: gray to off-white powder or granules
- Granule size: commonly in the ~1–4 mm band; many commercial grades are marketed around 2–4 mm for bulk blending and mechanized application
1.4 Water-soluble P2O5 (key quality indicator)
SSP is valued because most of its phosphate is in soluble form. References commonly describe ~85–90% of phosphate in superphosphate as water-soluble.
2) How SSP is made (manufacturing process)
2.1 Raw materials
- Phosphate rock (ground; quality affected by Fe/Al impurities)
- Sulfuric acid (commonly used in superphosphate manufacture)
In industrial practice, rock chemistry matters: elevated iron/aluminum can make the product sticky and harder to handle.
2.2 Core reactions (simplified + industrial context)
A commonly cited simplified reaction is:
Ca3(PO4)2 + 2H2SO4 → Ca(H2PO4)2 + 2CaSO4
Industrial references also note fluoride-related gases (e.g., HF/SiF4) can be released during the process, which is why off-gas control (scrubbing) is a standard design consideration.
2.3 Process flow (typical plant steps)
Crushing & grinding → Acidulation (reaction/mixing) → Den cooling → Curing → Milling/screening or granulation → Drying/cooling → Screening → Packing
After initial mixing, material is held briefly in a reactor/den, then moved to a storage pile/building for curing (reaction completion). Some references describe curing over several weeks, and cured SSP is often used as an additive in granular fertilizer production or granulated and sold directly.
3) Why SSP still matters (nutrient profile & agronomic value)
3.1 Triple-nutrient advantage: P + S + Ca
SSP’s agronomic advantage is often strongest where soils are deficient in sulfur and/or calcium. In studies where SSP outperforms more concentrated phosphate fertilizers, the benefit is frequently attributed to the S and/or Ca it contains—not only phosphorus.
3.2 Typical use cases
- Sulfur-deficient regions: cost-effective sulfur delivery bundled with phosphate
- Pastures and forage systems: where both P and S are needed
- Compound/blended fertilizers: as a phosphate + sulfur base for granular NPK blends
4) SSP vs TSP, DAP, and MAP (selection logic for buyers)
SSP is a lower-analysis phosphate fertilizer than TSP/DAP/MAP, but its built-in sulfur and calcium can make it more cost-effective on “nutrients delivered” in sulfur-deficient programs. Meanwhile, DAP/MAP provide nitrogen + phosphorus but do not inherently supply calcium and usually do not supply sulfur unless specially formulated.
- Choose SSP when you want P + S + Ca in one product, and when blending and soil programs benefit from gypsum-derived sulfur.
- Choose TSP when you need higher P concentration with minimal “ballast” and sulfur is not a priority.
- Choose DAP/MAP when nitrogen + phosphorus together fits the crop stage and nutrient plan.
5) Safety, handling & standards (quality and compliance)
5.1 Handling safety (plant + logistics)
SSP is strongly acidic (often reported pH < 2), so good industrial hygiene matters during manufacturing and handling (dust control, PPE, and moisture management to prevent caking).
5.2 China standard reference (optional compliance anchor)
In China, GB/T 20413-2017 is the national standard titled “Single superphosphate (过磷酸钙)”, covering terminology, requirements, test methods, inspection rules, marking, packaging, transport, and storage.
5.3 Heavy metals testing (ISO method reference)
ISO 17318:2015 specifies test methods for determining arsenic, cadmium, chromium, lead, and mercury in fertilizers (nitric-acid-soluble metals). It is commonly used as a reference method for fertilizer quality control programs. :contentReference[oaicite:12]{index=12}
6) Conclusion: SSP remains a practical, high-value phosphate fertilizer
Single super phosphate (SSP) remains globally important because it delivers phosphorus + sulfur + calcium in one reliable product, with high water-soluble phosphate performance and proven manufacturing scalability. For procurement and formulation, the best SSP decisions are made by specifying water-soluble P2O5, S, moisture, and particle size—not just total P2O5.
Compare Phosphate Fertilizers
See how SSP stacks up against TSP, DAP, and MAP in solubility, nutrient profile, and cost:
