How do you use calcium nitrate in drip irrigation and fertigation?
Calcium nitrate is one of the few fully soluble calcium sources for drip systems, and it also supplies nitrate nitrogen. Dissolve it in its own stock tank and inject it through a metered injector; do not put it in a concentrated stock with phosphates or sulphates, which form insoluble calcium phosphate or gypsum that plugs emitters.[2][5] To size the stock, work backwards from the target: at a 1:100 injector, 150 mg/L calcium in the line needs about 7.9 kg of 19%-Ca calcium nitrate per 100 L of stock (worked example below). Hard, alkaline water (about 2 meq/L bicarbonate and pH above 7.5) can precipitate calcium carbonate by itself, so test the water and acidify if needed.[4] Run the injector for at least 30–45 minutes and flush the lines for 30 minutes afterwards.[2]
Key facts at a glance
| Item | Value / answer |
|---|---|
| Fertilizer-grade analysis (HRSU) | HRSU supplies 18.5–19% calcium and 15.5% minimum nitrogen, 100% water-soluble, 0% insoluble residue (manufacturer specification, batch COA) |
| Common 15.5-0-0 grade | Often the double salt 5Ca(NO3)2·NH4NO3·10H2O with about 19% Ca[18] |
| Solubility in water | About 1,050 g/L at 0 °C and 1,290 g/L at 20 °C[18] |
| Incompatible in concentrate with | Phosphates, sulphates and thiosulphates[2] |
| Typical tank arrangement | Calcium nitrate alone in one concentrate tank, other nutrients in a second[5] |
| Minimum injection time | 30–45 minutes for uniform distribution[2] |
| Post-fertigation flush | At least 30 minutes of clean water[2] |
| Calcium carbonate risk | Bicarbonate above about 2 meq/L together with pH above about 7.5[4] |
| Calcium level that endangers phosphate injection | Calcium above 2–3 meq/L (about 40–60 mg/L)[4] |
| Greenhouse tomato solution pH target | 5.6–5.8; acid is injected if source water is above 5.8[5] |
| Suspended-solids clogging risk | Significant above 50 ppm; bacterial counts above 2,600 CFU may clog[1] |
| Tomato salinity threshold (soil / irrigation water) | ECe 2.5 dS/m and ECw 1.7 dS/m for full yield[9] |
| Injector ratio meaning | 1:100 gives 100 parts of final solution per part of stock; a 1:200 stock must be twice as concentrated[16] |
| Gypsum solubility | Roughly 2–2.5 g/L, far below calcium nitrate[19] |
Why is calcium nitrate used for drip fertigation?
Calcium nitrate supplies calcium and nitrate nitrogen in one soluble product. Extension guidance for blossom-end rot in tomato and pepper recommends delivering soluble calcium through the drip line, because foliar calcium sprays gave inconclusive results.[8] Calcium is only one part of a fertigation program: nitrogen, potassium and acidity are managed alongside it, and calcium nitrate is usually one tank in a multi-product setup. This page covers the delivery mechanics. For the crop physiology of calcium disorders see calcium nitrate for bitter pit and blossom-end rot, and for recirculating soilless systems see calcium nitrate in hydroponics.
Fertigation also saves inputs. A 2024 review from Punjab Agricultural University reports that applying fertilizer through drip saves about 20% of fertilizer and 20–35% of irrigation water across fruit crops.[14]
How much calcium and nitrogen does each crop get?
Rates depend on soil test, stage and water analysis, so treat the figures below as published extension examples, not a prescription for your field.
| Crop | Published guidance | Source |
|---|---|---|
| Tomato (field, Florida) | 200 lb N/acre per season; fertigate N and K in split doses | UF/IFAS[1] |
| Tomato (Georgia drip schedule) | 182 lb N/acre through fertigation, weekly N 7–17.5 lb/acre (peak weeks 7–10), maximum 20 lb N/week; liquid calcium nitrate (CN-9) at 5 gal/acre in rotation with other fertilizers | UGA[7] |
| Bell pepper | 192.5 lb N/acre through fertigation, maximum 20 lb N/week; same calcium nitrate rotation | UGA[7] |
| Watermelon | 112.5 lb N/acre through fertigation, maximum 15 lb N/week | UGA[7] |
| Cabbage | 246.5 lb N/acre; calcium to begin within 2 weeks of planting; N in at least three applications per week | UGA[7] |
| Tomato and pepper calcium timing | Inject soluble calcium from bloom until fruit is about golf-ball size; leaf Ca at early bloom 1.25–3.20% for tomato, 1.0–2.5% for pepper | UGA[8], UKY[11] |
| Citrus | Calcium nitrate (listed there as 14.5% nitrate-N plus 1% ammonium-N) can be blended with ammonium, magnesium and potassium nitrate; never with phosphates, sulphates or thiosulphates | UF/IFAS[2] |
| Cucumber and melon on saline water | Research trial: adding 5 mM calcium nitrate to drip water with 60 mM NaCl partly restored yield and leaf Ca and N | Kaya et al. 2003[15] |
Product analysis differs between suppliers (14.5% versus 15.5% N above), so always convert from the nutrient percentages on your own COA. As arithmetic, 20 lb N/week from a 15.5% N product is about 129 lb of product per acre, which also carries about 24 lb Ca at 19% Ca. Very high ammonium supply can worsen calcium disorders by competing with calcium uptake, which is why the Georgia schedule rotates calcium nitrate with other fertilizers.[7]
How do you calculate the stock and injector ratio?
Extension calculators use one idea: parts per million of a nutrient in the final water equals the concentration in the stock divided by the injector ratio.[5][16] Work from the target to the stock:
- Choose the target in the line. Example: 150 mg/L calcium.
- Multiply by the ratio. At 1:100 the stock must hold 150 × 100 = 15,000 mg/L = 15 g Ca per litre.[16]
- Convert to product. At 19% Ca, 15 ÷ 0.19 = 78.9 g per litre, or 7.9 kg per 100 L of stock (8.1 kg at 18.5% Ca).
- Check the nitrogen delivered. 78.9 g × 0.155 = 12.2 g N per litre of stock, so about 122 mg/L N in the line at 1:100. This is a side effect you must count in your nitrogen budget.
- Change ratio, not chemistry. At 1:200 the same final concentration needs twice the stock strength, about 15.8 kg per 100 L, which is still far below the salt's solubility.[16][18]
A published worked example gives the same method: 166 ppm Ca from 19% Ca product is 330 g per 100 US gallons of final solution, which also delivers about 135 ppm N at 15.5% N.[6] Mississippi State's injector bulletin uses the same ppm formulas and notes that fertilizer must be measured accurately because injector systems are precise.[5] Weigh fertilizer rather than measuring by volume.[16]
An older HRSU guide quoted stock tanks of 10–20 kg per 100 L. We could not tie that range to a published source. It is best read as common practice: the real limit is set by your injector ratio and demand, not by solubility, because calcium nitrate dissolves at over 1,000 g/L.[18] Mississippi State notes that solubility limits are not a problem for most common greenhouse fertilizers.[5]
Does calcium nitrate dissolve slowly or cool the tank?
Solubility rises with temperature, from about 1,050 g/L at 0 °C to 1,290 g/L at 20 °C.[18] Dissolving the tetrahydrate is endothermic, which is why it is used in cold packs, so a big batch in cold water cools the tank and can slow dissolution.[18] Our source for the endothermic behaviour is encyclopedic only, so we advise watching the tank temperature rather than relying on a number. If something will not dissolve, stir with a pump or mixer, or use warm water; Mississippi State suggests circulating or mechanical mixing, or hot water, when solubility problems arise.[5] Do not let a cold-night stock sit with undissolved solids reaching the injector.
Why does calcium nitrate need its own tank, and what precipitates?
Calcium forms three insoluble solids that matter in drip lines. Keep them in mind when you plan tanks.
- Calcium phosphate. Calcium with phosphorus in a concentrate forms calcium hydrogen phosphate, described as a very hard precipitate that clogs injectors and irrigation systems; in diluted solutions the reaction does not occur.[5] Florida extension also lists tomato fertigation with calcium nitrate as less common because of phosphate precipitation and advises keeping combined calcium and magnesium below 50 ppm where phosphate is present.[1]
- Gypsum (calcium sulphate). Calcium injected with any sulphate fertilizer forms gypsum, and fertilizers containing calcium should be flushed from tanks, pumps, filters and tubing before phosphorus, urea-ammonium nitrate or urea-sulphuric fertilizer is injected.[3] Gypsum dissolves only to about 2–2.5 g/L.[19]
- Calcium carbonate. Hard water can scale emitters even with no fertilizer: bicarbonate above about 2 meq/L with pH above about 7.5 is the warning zone, and adding calcium can raise the risk.[4]
Tank labels differ between sources. Mississippi State calls the calcium nitrate tank “B” and the tank for other nutrients “A”,[5] while many growers reverse the letters. The rule is the same: calcium nitrate and its compatible partners in one tank, phosphates and sulphates in another. UF/IFAS lists calcium nitrate as compatible with ammonium, magnesium and potassium nitrate,[2] and Utah State warns that phosphate and sulphate forms precipitate with calcium;[3] the UC compatibility chart is worth checking before any new mix.[17]
Should you acidify the water?
Acid can help in two different ways. In alkaline, bicarbonate-rich water, K-State advises lowering pH to 7.0 or below by continuous injection to stop calcium carbonate scale.[4] For soilless greenhouse tomato, Mississippi State uses an extra injector head to hold solution pH at 5.6–5.8 when source water is above 5.8.[5] Florida extension lists hydrochloric, sulphuric, citric and phosphoric acid as options and advises flushing after acid injection to limit precipitation and corrosion.[1] Choose the acid with the rest of the program in mind: phosphoric acid must not be mixed with calcium fertilizer because it forms insoluble calcium phosphate, and sulphuric acid adds sulphate that can combine with calcium downstream.[2][3] Use acid from its own tank and handle it under its safety data sheet.
How do you prevent filtration and clogging problems?
- Test the water first. Florida guidance flags suspended solids above 50 ppm and bacterial counts above 2,600 CFU as clogging risks.[1] K-State lists pH, hardness, bicarbonate, iron, sulphide and solids among the tests to run.[4]
- Size filtration to the emitter. A general rule is to remove particles one-tenth the size of the smallest emitter opening.[4]
- Jar test before every new mix. Mix fertilizer with irrigation water and watch for precipitate or milkiness for 1–2 hours.[2] North Carolina advice also suggests a small jar batch of the intended mix.[12]
- Flush. Run clean water for at least 30 minutes after fertigation.[2]
- Use a fully soluble grade. Undissolved fertilizer settles and can clog emitters.[5] Check the insoluble-residue figure on the COA for any product, powder or granular. See powder vs granular calcium nitrate.
- Protect the water supply. Install backflow prevention and check valves before injecting chemicals into any irrigation system.[10]
What EC should the fertigation water have?
Our earlier page gave a feed EC of 1.5–2.5 dS/m. That range is typical practice for many fruiting vegetables but we could not source it as a standard, so use your crop's own guidance. What is published is the yield threshold of the crop to salinity: tomato loses no yield up to ECe 2.5 dS/m in the root zone, which corresponds to ECw 1.7 dS/m for irrigation water, and cucumber has the same thresholds.[9] Fertilizer adds to water EC, so measure EC of the final line and compare it to the crop's tolerance and your leaching practice.
How should injections be scheduled?
- Split nitrogen into frequent small doses; Georgia schedules use weekly rates with peaks mid-season and at least three applications per week for cabbage.[7]
- Inject for at least 30–45 minutes inside the irrigation cycle so nutrients reach the whole system, then flush.[2]
- Time calcium for the demand window: from bloom to golf-ball-size fruit in tomato and pepper.[8] Also keep soil moisture steady, because irregular water supply and low soil pH contribute to blossom-end rot.[11][12]
- Do not stack urea on a high-pH wet surface without irrigating afterwards; see the alternatives table.
What are the alternatives to calcium nitrate in fertigation?
| Option | What it gives | Fertigation issues |
|---|---|---|
| Calcium nitrate | Soluble Ca and nitrate-N | Own tank; incompatible with phosphates and sulphates[2][5] |
| Calcium ammonium nitrate (CAN) | Ca and N in a different ratio[20] | Supplies less calcium per unit of nitrogen than calcium nitrate; the UC compatibility chart lists incompatibilities with several phosphate, sulphate and UAN products[17]. See calcium nitrate vs CAN |
| Calcium chloride | Ca, chloride | No nitrogen; adds chloride. UKY found foliar CaCl2 sprays not effective for blossom-end rot[11]. See calcium nitrate vs calcium chloride |
| Gypsum | Ca and sulphur, no nitrogen | Only about 2–2.5 g/L soluble, so no concentrated stock[19] |
| Urea or UAN | N only, no calcium | Urea can volatilise: an Oregon trial lost over 60% of applied N without irrigation, under 5% with 0.45 inch of irrigation[13]; UAN-32 is on the incompatible list with calcium nitrate[17] |
| Potassium nitrate or ammonium nitrate | N (and K), no calcium | Compatible with calcium nitrate[2]; much ammonium can compete with calcium[7] |
Common mistakes
- Premixing calcium nitrate with MAP, MKP or magnesium sulphate in one concentrate.[5]
- Injecting phosphoric acid into a line carrying calcium.[2]
- Skipping the jar test with new water or a new product.[2]
- Ending the cycle on fertilizer instead of flushing.[2]
- Ignoring bicarbonate and pH, then blaming the fertilizer for scale.[4]
- Treating a published N rate as a calcium rate: calcium nitrate is only about 15.5% N.
When calcium nitrate is NOT the right choice
- Do not mix with phosphates, sulphates or thiosulphates in a concentrate. Insoluble calcium phosphate or gypsum plugs injectors and emitters.[2][5]
- Not a complete nitrogen program. It is about 15.5% N and 19% Ca; high-N crops need other nitrogen sources, while excess ammonium can compete with calcium.[7]
- Not a fix for hard, bicarbonate-rich water. Scaling needs acidification and monitoring, and adding calcium can increase the carbonate risk.[4]
- Not a substitute for water management. Blossom-end rot also follows drought stress and low soil pH, so calcium alone may not cure it.[12]
- Rates here are examples. Confirm against your crop, soil test and local extension service.
What HRSU supplies — and what it does not
HRSU Indore supplies fertilizer-grade calcium nitrate powder: 18.5–19% calcium, 15.5% minimum nitrogen, 100% water-soluble with 0% insoluble residue, in 25 kg and 50 kg bags, with a batch COA, bulk and export supply, and TDS and SDS on request. HRSU does not claim any other grade or certification. Use the COA calcium percentage in the stock calculation above, run a jar test with your own water, and ask for a sample before ordering a full season's quantity.
Need drip-grade calcium nitrate?
100% water-soluble · 0% insoluble residue · 25 kg & 50 kg bags · bulk/export available.
Buy online WhatsApp usFrequently asked questions
Does calcium nitrate clog drip emitters?
Can I mix calcium nitrate with other fertilizers in one tank?
Only with compatible nitrates such as ammonium, magnesium and potassium nitrate; never with phosphates, sulphates or thiosulphates in a concentrate.[2]
How do I calculate how much calcium nitrate to put in the stock tank?
What EC should my calcium nitrate feed be?
There is no single standard. A tomato crop tolerates root-zone ECe 2.5 dS/m (ECw 1.7 dS/m) without yield loss, so keep the final feed within your crop's tolerance and verify at the dripper.[9]
Why does the calcium nitrate tank get cold?
Do I need to acidify water when using calcium nitrate?
How long should I inject and flush?
Inject for at least 30–45 minutes and then flush with clean water for at least 30 minutes.[2]
Related guides
- Calcium nitrate in hydroponics and greenhouses
- Calcium nitrate for bitter pit and blossom-end rot
- Powder vs granular calcium nitrate
- Calcium nitrate vs CAN
References
- Key Fertigation Information for Tomato Production (HS1392) — UF/IFAS Extension, University of Florida. University extension
- Fertigation for Citrus Trees (HS1306), Zekri et al. — UF/IFAS Extension, University of Florida. University extension
- Fertigation Facts — Utah State University Extension. University extension
- MF2575 SDI Water Quality Assessment Guideline (Rogers, Lamm, Alam) — Kansas State University Research and Extension. University extension
- Injector Planner: A Spreadsheet Approach to Fertilization Management for Greenhouse Tomatoes (Bulletin 1003, Snyder) — Mississippi State University, 1993. University extension
- Crop Management Practices and Fertigation (Bedasie) — CARDI, Caribbean Agricultural Research and Development Institute. Regional agricultural institute
- Drip Fertilizer Schedule Recommendations for Vegetable Crops in Georgia Coastal Plain Soils (C1325) — University of Georgia Extension. University extension
- Blossom-End Rot and Calcium Nutrition of Pepper and Tomato (C938), Westerfield, Mayfield, Kelley, 2022 — University of Georgia Extension. University extension
- Water quality for agriculture, FAO Irrigation and Drainage Paper 29 (Ayers and Westcot), Table 4 crop salinity tolerance — Food and Agriculture Organization of the United Nations. Intergovernmental body
- Chemical Injection Methods for Irrigation (CIR864), Haman and Zazueta — UF/IFAS Extension, University of Florida. University extension
- Blossom End Rot (CCD-FS-11) — Center for Crop Diversification, University of Kentucky. University extension
- Note 7: Fertilization of Tomato Grown under Plasticulture — North Carolina Department of Agriculture and Consumer Services. State government agency
- Factors Affecting Nitrogen Fertilizer Volatilization (EB0208, Jones), updated 2020 — Montana State University Extension. University extension
- Fertigation Technology for Fruit Crops (Sharda et al., 2024) — Indian Journal of Horticulture, ICAR; Punjab Agricultural University. Peer-reviewed
- Ameliorative effect of calcium nitrate on cucumber and melon plants drip irrigated with saline water (Kaya, Kirnak, Tas, Higgs, 2003) — Journal of Plant Nutrition, via University of Hertfordshire repository. Peer-reviewed
- Fertilizer calculations for greenhouse crops — UMass Amherst Extension, Greenhouse Crops and Floriculture. University extension
- Maintenance of Microirrigation Systems (fertilizer compatibility) — University of California Agriculture and Natural Resources. University extension
- Calcium nitrate — Wikipedia. Encyclopedia
- Gypsum — Wikipedia. Encyclopedia
- Calcium ammonium nitrate — Wikipedia. Encyclopedia