Reviewed August 2026 against USGS Mineral Commodity Summaries 2025 and University of Illinois farmdoc daily.

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What the Three Numbers Mean

20-5-10, 13-13-13, and 30-10-10 are all NPK fertilizer grades, and the three numbers always mean the same thing regardless of which blend you’re holding: percent nitrogen (N), percent available phosphate (P₂O₅), and percent potash (K₂O), by weight, guaranteed on the bag under US fertilizer labeling law. 20-5-10 is a nitrogen-heavy lawn and turf blend used where fast green-up matters more than root or fruit development. 13-13-13 (“triple thirteen”) is a balanced, general-purpose blend spread across vegetable gardens, pastures, and row crops that need roughly equal N-P-K. 30-10-10 is a high-nitrogen blend aimed at leafy growth in acid-loving ornamentals, turf, and some forage systems. The remaining weight in every bag — 65% of a 20-5-10 bag, for instance — is filler: inert granular carrier that makes the nutrient percentages spreadable at a consistent rate.

What differs between the three is the source of that middle number, the phosphate. Every bag of P₂O₅ in a 13-13-13 or 20-5-10 blend traces back to phosphate rock — a sedimentary or igneous ore dominated by apatite minerals — that was mined, concentrated, and run through a wet-acid process before it ever reached a spreader. Understanding that supply chain explains both why phosphate-heavy blends cost more per unit of nutrient than nitrogen-only products, and why the mineral group behind the “P” in NPK is worth knowing on its own terms.

20-5-10 Fertilizer: What It’s Used For

Primary Uses

• Lawn and turf maintenance: the dominant use case searched for this grade. High nitrogen drives chlorophyll production and the green color and density homeowners and turf managers want; the modest phosphate keeps established root systems maintained without over-feeding phosphorus that established turf rarely needs.
• Pasture and hay ground topdressing: where forage grasses need a nitrogen push for tonnage but soil tests already show adequate phosphorus reserves.
• Established woody ornamentals and shade trees: where the goal is foliage density rather than new root or flower development.

Why Not Use 20-5-10 Everywhere Nitrogen Is Needed?

Because the 5% phosphate is a floor, not a bonus. On soils that test low in phosphorus — common on sandy or heavily cropped ground — 20-5-10 supplies too little P₂O₅ to correct a deficiency even as it oversupplies nitrogen. A soil test, not the bag number, should confirm whether the phosphate rate matches what the field actually needs; land-grant extension soil-test labs (Cooperative Extension programs run through each state’s land-grant university) report exactly this breakdown for a modest sample fee.

13-13-13 Fertilizer: Uses

Primary Uses

• Vegetable gardens and home horticulture: equal nutrient supply suits crops like tomatoes, peppers, and squash during establishment, before fruiting-stage potassium demand rises further.
• Row-crop starter applications: banded near the seed at or before planting, where balanced early nutrition supports both root development (phosphate) and vegetative growth (nitrogen) simultaneously.
• Pasture and hayfield renewal: where a soil test shows all three nutrients — not just nitrogen — need rebuilding, typically after several seasons of hay removal without replacement.
• New lawn establishment and sod: unlike an established lawn’s 20-5-10 maintenance feeding, new turf benefits from 13-13-13’s higher phosphate share to drive root-system establishment.

Why “Balanced” Doesn’t Mean “Always Right”

A 1:1:1 ratio is a reasonable default precisely because it doesn’t over-commit to any one nutrient — but that also means it’s rarely the optimal choice once a soil test comes back. A field that’s already high in potassium and low in nitrogen is better served by a lopsided blend than by paying for potash it doesn’t need. Treat 13-13-13 as the blend to reach for when no soil test exists yet, and as the blend to move away from once one does.

30-10-10 Fertilizer: What It’s Used For

Primary Uses

• Acid-loving ornamentals: azaleas, camellias, and rhododendrons are the textbook use case — 30-10-10 formulations are frequently paired with acidifying carriers for exactly this market.
• Fast-establishment turf and sod farms: where rapid canopy closure is the commercial goal and phosphorus/potassium reserves in the growing medium are already managed separately.
• Container and greenhouse ornamental production: soilless media holds little native nutrient reserve, so growers supply all three numbers, weighted toward nitrogen for foliage crops.
• Non-fruiting foliage houseplants: where the growth goal is leaf mass, not flowering or fruiting.

Where 30-10-10 Is the Wrong Choice

Flowering and fruiting plants — tomatoes setting fruit, or perennials budding — are poorly matched to 30-10-10: excess nitrogen relative to phosphate and potash pushes vegetative growth at the expense of bloom and fruit set. Row-crop growers rarely reach for a 30-10-10 grade at all; it’s a specialty-nursery and turf-establishment product, not a field-crop staple, which is one reason it returns fewer and lower-volume searches than 20-5-10 or 13-13-13.

Side-by-Side: 20-5-10 vs 13-13-13 vs 30-10-10

All three numbers in every grade are legally guaranteed minimums under state fertilizer-labeling statutes modeled on the Association of American Plant Food Control Officials (AAPFCO) uniform bill — the percentages on the bag are not marketing copy, they’re what a state feed-and-fertilizer inspection lab would find if it tested that batch.

The Group of Phosphate Minerals Behind Every NPK Bag

Whichever grade you buy, the phosphate share of every bag started life as rock. The group of phosphate minerals used in fertilizer is dominated by apatite-group minerals and the sedimentary rock built from them, phosphorite.

• Fluorapatite — chemical formula Ca₅(PO₄)₃F — is the primary phosphate mineral in most commercial phosphorite deposits.
• Hydroxyapatite — chemical formula Ca₅(PO₄)₃OH — occurs as a secondary phosphate mineral alongside fluorapatite in the same ore bodies.
• Phosphorite is the sedimentary rock, largely cryptocrystalline apatite, that makes up the bulk of mined phosphate ore worldwide.
• Struvite — magnesium ammonium phosphate, NH₄MgPO₄·6H₂O — is a secondary phosphate mineral increasingly recovered from municipal and agricultural wastewater rather than mined, and is used as a slow-release phosphate source.

Commercial phosphate rock ore runs 15–20% P₂O₅ by weight as mined, per USGS’s Mineral Commodity Summaries — well below the 44–52% P₂O₅ content of a finished fertilizer product like triple superphosphate, which is why beneficiation (covered next) exists at all.

Where US Phosphate Rock Comes From

The United States produced an estimated 20 million tonnes of marketable phosphate rock in 2024, valued at $2 billion, according to USGS’s Mineral Commodity Summaries 2025. Florida and North Carolina together accounted for 75% of that US production in 2024 — the two states remain the backbone of domestic phosphate mining. Nationally, 95% of phosphate rock mined is used as feedstock for fertilizer manufacture, principally as the wet-process phosphoric acid route described in the next section; the remaining 5% goes to animal feed supplements, industrial phosphoric acid, and other non-fertilizer chemical uses.

From Phosphate Rock to Bagged Fertilizer

1. Extraction

Phosphate rock is mined from open-pit operations — Florida’s Bone Valley district and North Carolina’s Aurora district are the two production anchors behind that 75% US share cited above. Draglines and mechanical excavation remove the phosphate-bearing matrix, which is then slurried and pumped to a beneficiation plant.

2. Beneficiation — Concentrating the Phosphate Value

Mined ore is rarely pure apatite; it carries clays, sand, and carbonate gangue that dilute its P₂O₅ value below the 15–20% run-of-mine baseline. Washing, screening, and froth flotation strip out the gangue and raise the concentrate toward marketable grade.

3. Conversion to Phosphoric Acid: The Wet Process

Beneficiated concentrate reacts with sulfuric acid in the wet-acid process, the dominant route for turning rock into fertilizer-grade phosphorus:

The reaction yields phosphoric acid (H₃PO₄), the intermediate from which monoammonium phosphate (MAP), diammonium phosphate (DAP), and triple superphosphate (TSP) are all manufactured — and which then gets blended with nitrogen and potash sources into finished grades like 20-5-10, 13-13-13, and 30-10-10. Gypsum (CaSO₄·2H₂O), known in this context as phosphogypsum, is the co-product, produced at roughly 5 tonnes for every tonne of P₂O₅ recovered.

4. Blending Into Finished NPK Grades

Phosphoric acid or its solid derivatives (MAP, DAP, TSP) are combined with a nitrogen source — urea or ammonium nitrate — and a potash source (potassium chloride is most common) in the ratios needed to hit a target grade. Getting to 20-5-10 versus 13-13-13 versus 30-10-10 is a blending-ratio decision made at the fertilizer plant, not a difference in which minerals go in; the same phosphate-rock-derived inputs feed all three.

What These Fertilizers Cost and Why

Blended NPK price tracks its two most volatile inputs: nitrogen source cost and phosphate/potash source cost. The University of Illinois farmdoc daily service, which tracks Illinois wholesale fertilizer markets for Corn Belt growers, reported anhydrous ammonia (82% N) at $786 per tonne and urea (46% N) at $594 per tonne in Illinois in August 2025. Because nitrogen is the dominant cost driver in a high-N grade, a 30-10-10 or 20-5-10 blend moves more with ammonia and urea pricing than a lower-N grade like 13-13-13 does.

farmdoc daily’s 2026 crop-year projections put total fertilizer cost at $166 per acre for corn and $57 per acre for soybeans — a gap that reflects corn’s much higher nitrogen requirement relative to soybeans, which fix a share of their own nitrogen biologically and are typically fertilized closer to a starter-and-potash program than a full N-P-K regime.

Neither figure separates out cost by NPK grade — farmdoc daily’s dataset tracks nitrogen-source and total per-acre cost, not a per-bag price for 20-5-10 versus 13-13-13 versus 30-10-10 specifically. No published dataset in this research breaks out price or acreage by individual NPK blend; if you need a current price for a specific grade, the most direct method is to call two or three regional co-ops or ag retailers and ask their posted price per ton for that exact grade, since blended-fertilizer pricing is set locally based on the retailer’s own nitrogen, phosphate, and potash input costs plus blending and delivery. For the underlying commodity inputs, USDA’s Agricultural Marketing Service publishes weekly anhydrous ammonia spot pricing at its Market News reports page, which is the fastest way to track the input that moves high-nitrogen grade pricing week to week.

What Drives the Volatility

• Natural gas prices: ammonia synthesis is natural-gas-intensive, so gas price swings flow directly into anhydrous ammonia and urea cost.
• Phosphate rock and sulfur costs: since wet-process phosphoric acid consumes both, disruptions to either input market move MAP/DAP/TSP cost, and from there the phosphate share of blended grades.
• Potash source cost: potassium chloride pricing, set largely by a small number of major exporting basins, affects the K side of every blend equally.
• Regional freight and blending margin: local co-op delivered price adds transport and blending cost on top of the underlying commodity inputs, which is why the same grade can price differently county to county.

Calculator: Compare Nutrient Cost per Acre

Enter your delivered price per ton for a grade and your acreage to see cost per acre and cost per pound of actual nitrogen — the number that lets you compare 20-5-10, 13-13-13, and 30-10-10 on equal footing regardless of bag size.

Assumes a 2,000 lb ton and a single blended product with no blending or spreading surcharge beyond the delivered price you enter. It does not include phosphate or potash cost per unit separately, freight beyond what’s already in your delivered price, or application labor/equipment cost — use it to compare nitrogen cost across grades, not total input budget.

Choosing and Applying the Right Blend

1. Start With a Soil Test, Not the Bag

Every land-grant university's Cooperative Extension office runs a soil-test lab that reports current N, P, and K status along with pH, typically for a fee in the $10–20 range depending on the state and panel selected. That result — not a general preference for "balanced" or "high-nitrogen" fertilizer — should determine whether 20-5-10, 13-13-13, 30-10-10, or a different custom blend altogether fits a given field or bed this season.

2. Match Grade to Growth Stage and Crop Type

• Establishment (new lawns, seedlings, transplants): favor higher-phosphate blends like 13-13-13 to support root development.
• Maintenance (established turf, mature pasture with adequate P and K): a nitrogen-forward grade like 20-5-10 avoids paying for nutrients the soil already holds.
• Foliage-focused ornamental and greenhouse production: 30-10-10's high nitrogen share suits leaf mass goals but should be avoided once a plant shifts to flowering or fruiting.

3. Application Method and Timing

• Banding near the root zone at or before planting maximizes early phosphate uptake for starter applications like 13-13-13.
• Broadcast topdressing suits maintenance nitrogen applications like 20-5-10 on established turf or pasture.
• Split applications reduce the risk of nitrogen loss on high-N grades like 30-10-10, particularly under irrigation or in high-rainfall periods.

Runoff, Phosphogypsum, and Responsible Use

Environmental Considerations Specific to These Blends

• Runoff risk scales with the phosphate number, not the nitrogen number: a 13-13-13 applied at a rate calibrated for its nitrogen content will typically oversupply phosphate relative to crop need, since most field crops need less P₂O₅ than N pound-for-pound.
• Phosphogypsum management: the gypsum co-product from wet-process phosphoric acid manufacture (roughly 5 tonnes per tonne of P₂O₅) requires controlled stacking due to naturally occurring trace radioactivity, and is a regulated byproduct at US phosphoric acid plants.
• Resource longevity: Florida and North Carolina's combined 75% share of 2024 US phosphate rock output means US fertilizer supply is geographically concentrated; tracking new deposit development matters for long-run domestic supply.

Pathways to More Precise Use

• Soil-test-driven rates rather than blanket application of any single grade across an entire operation.
• Banded or split applications to reduce the phosphate and nitrogen surplus available for runoff at any one time.
• Non-invasive exploration for new phosphate sources: satellite-driven 3D mineral prospectivity mapping can evaluate deposits without the ground disturbance of exploratory drilling. See how 3D mapping with Farmonaut supports sustainable mineral discovery →

Satellite Mineral Intelligence for Phosphate Exploration

Behind every bag of 20-5-10, 13-13-13, or 30-10-10 sits a mined phosphate deposit somewhere upstream. Farmonaut applies satellite data analytics and AI-driven mineral prospectivity mapping to identify and evaluate new phosphate sources — and deposits of over a dozen other mineral types — without ground disturbance during early exploration.

How It Works

• Clients provide coordinates or a region of interest for phosphate (or other mineral) exploration.
• Farmonaut selects the multispectral or hyperspectral satellite data best suited to the target mineral's spectral signature.
• AI models process those spectral signatures to flag high-prospect zones for follow-up ground work.
  
  Explore the Satellite Driven 3D Mineral Prospectivity Mapping report sample for a visual walkthrough.

Why It Matters for Phosphate Specifically

• Faster targeting: replaces months of manual fieldwork with data-driven prospectivity maps, cutting exploration timelines meaningfully before any drilling begins.
• Lower upfront footprint: zero ground disturbance during the early screening phase, ahead of any physical exploration.
• Global reach: supports exploration across continents and mineral types, including phosphate alongside gold, lithium, copper, and cobalt.

FAQ

What is 20-5-10 fertilizer used for?

20-5-10 supplies 20% nitrogen, 5% phosphate, and 10% potash — a nitrogen-heavy ratio used mainly for established lawn and turf maintenance, pasture topdressing, and mature ornamentals where fast green growth matters more than new root or flower development.

What is 13-13-13 fertilizer used for?

13-13-13 supplies equal parts nitrogen, phosphate, and potash. It's a general-purpose starting blend for vegetable gardens, row-crop starter applications, new lawn or sod establishment, and pasture renovation — anywhere a soil test hasn't yet pointed toward a more lopsided ratio.

What is 30-10-10 fertilizer used for?

30-10-10 is a high-nitrogen, 3:1:1 blend used for acid-loving ornamentals (azaleas, camellias, rhododendrons), sod farms, and greenhouse or container foliage production, where rapid leaf and stem growth is the goal. It's a poor fit for flowering or fruiting plants and is rarely used on field row crops.

What is the group of phosphate minerals used in fertilizer?

The phosphate share of any NPK fertilizer, including 20-5-10, 13-13-13, and 30-10-10, comes from apatite-group minerals — chiefly fluorapatite (Ca₅(PO₄)₃F) and hydroxyapatite (Ca₅(PO₄)₃OH) — and the sedimentary rock built from them, phosphorite. Struvite (NH₄MgPO₄·6H₂O), recovered from wastewater, is a smaller secondary source.

Is 13-13-13 better than 20-5-10 or 30-10-10?

Neither grade is universally better — each is built for a different nutrient gap. 13-13-13 suits establishment and unknown-soil situations; 20-5-10 suits maintenance feeding where phosphorus and potassium are already adequate; 30-10-10 suits foliage-focused growth on acid-loving or non-flowering plants. A current soil test is the only reliable way to choose among them for a specific field or bed.

How much does 13-13-13 or 20-5-10 cost per acre?

No public dataset breaks out price by individual NPK grade. University of Illinois farmdoc daily reports the underlying nitrogen commodity costs — anhydrous ammonia at $786/tonne and urea at $594/tonne in Illinois in August 2025 — and projects total 2026 fertilizer cost at $166/acre for corn and $57/acre for soybeans. For a specific grade's delivered price, ask a regional co-op or ag retailer directly, since blend pricing is set locally from current N, P, and K input costs plus blending and freight.

Why does phosphate fertilizer cost more per unit of nutrient than nitrogen fertilizer?

Because phosphate's supply chain runs through mining and wet-process acid manufacture — extraction, beneficiation, and a sulfuric-acid reaction — while nitrogen fertilizer like urea or anhydrous ammonia is synthesized from atmospheric nitrogen and natural gas. The mineral supply chain adds mining, beneficiation, and byproduct-management costs that a gas-based nitrogen process doesn't carry.

Conclusion & Next Steps

The fastest way to pick among 20-5-10, 13-13-13, and 30-10-10 is to match the ratio to the job: nitrogen-heavy 20-5-10 for maintaining growth that's already established, balanced 13-13-13 for establishing new growth or when no soil test has ruled otherwise, and high-nitrogen 30-10-10 for foliage-focused ornamentals and greenhouse production. None of that changes what's inside the bag — every gram of phosphate in any of the three traces back to the same group of phosphate minerals, principally fluorapatite and hydroxyapatite mined as phosphorite, concentrated, and converted to phosphoric acid before blending.

For growers and land managers, a current soil test remains the durable check that outlasts any single year's price table: it tells you which of the three ratios — or a custom blend altogether — actually matches your field's nutrient status right now. For mining and exploration professionals tracking where that phosphate supply originates, Farmonaut's satellite-based mineral detection and 3D prospectivity mapping support earlier, more sustainable identification of new deposits.

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Sources cited in this article: USGS Mineral Commodity Summaries 2025 — Phosphate Rock, University of Illinois farmdoc daily — Fertilizer Decisions for the 2026 Crop Year, and Geology.com — Apatite Mineral Data.