How to Select the Right Fertilizer for Hydroponics
Developing a Nutrient Program
- Laboratory analysis of your water
- Take different nutrient sources into account (substrate, water, fertilizer)
- Different crops may have different needs
- Numerous published nutrient solution formulations exist
- For vegetative crops, most nutrient-solution recipes don’t adjust the ratio of nutrients while they grow
- In fruiting crops, the ratio may be adjusted to alter the shift between vegetative and reproductive growth
- Most new growers use one recipe that works well for a range of crop growth stages and conditions
Optimize Nutrient Solution Formulation Based on:
- Crop grown
- Plant growth stage (vegetative, reproductive, etc.)
- Changing environmental conditions (light intensity and duration, temperature, etc.)
- Changing plant stress conditions (increase or decrease EC)
- Changing pH of the rooting medium
- Need to alter nutritional status of plant to counter an insufficiency
14 Essential Elements
Thus, 12 elements applied in a fertilization program.
Elements: |
Atomic number: |
Nitrogen |
7 |
Phosphorus |
15 |
Potassium |
19 |
Magnesium |
12 |
Sulfur |
16 |
Calcium |
20 |
Baron |
5 |
Chlorine |
17 |
Manganese |
25 |
Iron |
26 |
Nickel |
28 |
Copper |
29 |
Zinc |
30 |
Molybdenum |
42 |
Hydrogen |
1 |
Carbon |
6 |
Oxygen |
8 |
Concentration in Dry Tissue
Elements: |
Symbol: |
ppm: |
%: |
Carbon |
C |
450,000 |
45 |
Oxygen |
O |
450,000 |
45 |
Hydrogen |
H |
60,000 |
6 |
Nitrogen |
N |
15,000 |
1.5 |
Potassium |
K |
10,000 |
1.0 |
Calcium |
Ca |
5,000 |
0.5 |
Magnesium |
Mg |
2,000 |
0.2 |
Phosphorus |
P |
2,000 |
0.2 |
Sulfur |
S |
1,000 |
0.1 |
Concentration in Dry Tissue
Elements: |
Symbol: |
ppm: |
%: |
Chlorine |
Cl |
100 |
0.01 |
Iron |
Fe |
100 |
0.01 |
Manganese |
Mn |
50 |
0.005 |
Boron |
B |
20 |
0.002 |
Zinc |
Zn |
20 |
0.002 |
Copper |
Cu |
6 |
0.0006 |
Molybdenum |
Mo |
0.1 |
0.00001 |
Source: Ames, M. and Johnson, W.S., 1986, in Proceedings of the 7th Annual Conference on Hydroponics: The Evolving Art, The Evolving Science, Hydroponics Society of America, Concord, CA.
Irrigation Water Quality Guidelines
mg∙L-1 = ppm
Alkalinity
- Ability of water to neutralize acids; it buffers water against changes in pH
- Reported in terms of parts per million (ppm) CaCO3 or milli-equivalent (meq∙L-1)
- Water alkalinity can vary between 50-500 ppm (1-10 meq∙L-1)
- Alkalinity affects how much acid is required to change the pH
Alkalinity (meq·L-1)
Correcting High Alkalinity
Greenhouse substrate and management, D.A. Bailey, W.C. Fonteno and P.V. Nelson, NCSU
Irrigation Water Quality Guidelines
mg∙L-1 = ppm
Chemical Properties of Growing Media
- pH Controls the availability of all essential plant nutrients
- pH range 5.4 – 6.0 for solution culture and soilless media
- pH range 6.2 – 6.0 for soil-based media
- Too high pH: caused by highly alkaline water, excess lime, calcium nitrate fertilizers
- P, Fe, Mn, Zn, Cu and B tied up
- Too low pH: Caused by acid forming fertilizers NH + 4
- Ca, Mg, S, Mo tied up. Excessively soluble Fe, Mn, and Alreact with P to render it insoluble
Selection of Fertilizer
- Proportion of potassium (K2O:N)
- Proportion of phosphate (N:P2O)
- Form of Nitrogen
- Ammonium (NH4+), small amounts
- Nitrate (NO3 ), majority
- Urea, small amounts
- Nitrate nitrogen tend to have basic reaction, raising media pH
- Ammonium sources of nitrogen will have an acid reaction, lowering media pH
- In an acidic environment NO -3 is more readily absorbed, while NH +4 is better absorbed at a higher pH
- At pH 6.8, both ionic species are taken up equally
Ammonium and Nitrate Nitrogen Calculation
Nitrogen Fertilizer and pH Relationship
Nitrogen Fertilizer and pH Relationship
Fertilizer Options for the Grower
- One-part mixes (All-Purpose)
- Provide all the required nutrients in one bag
- Pick desired concentration and measure out the required amount
- Usually not for stock solutions, unless label says otherwise
- Two or three-part mixes, two stock tanks (Base plus Customizing)
- N-P-K mix, CaNO3, MgSO4
- Using two tanks, a concentrated stock solution can be made (no precipitation)
- Tank A – calcium and chelated iron
- Tank B – phosphates and sulfates
- Separate tank for acid or add to Tank B
- Many-part mixes
- Hobbyists
- Easy to prepare but higher shipping costs
- Liquid blends
- Individual compound fertilizers can be used to formulate your own mix
- Grower has full control over formulation
- Cost effective for huge operations
- Up to 11 fertilizers mixed and stored separately
Common Nutrient Ranges in Nutrient Solutions
Nutrient Solution Recipes: Open vs. Closed Systems
De Kreij et al. 1991 (Netherlands) and Deckers, 2004 (Belgium)
Compare
Always Compare Solution Composition
Lettuce, Herbs, Leafy greens
Target Nitrogen Feed Rates (ppm)
Solution adjustment – Tomato Nutrition, K:N ratio
- Optimal ratio of K to N varies with growth stage
- When the first truss is in flower, the K:N ratio should be 1.2:1, which is the same K:N requirement as in most plants during the vegetative stage
- This ratio increases to 2:1 as the fruit load on the plant increases, since about 70% of the potassium absorbed moves into the fruit
- By the time the ninth cluster flowers open, the ratio should be 2.5:1
Tomato Nutrient Solution Recipe
Information Resources
University resources – Extension publications
Professional magazines
– Greenhouse Management, www.greenhousemag.com
– Greenhouse Grower, www.greenhousegrower.com
– Greenhouse Canada, www.greenhousecanada.com
Books
– Greenhouse Technology and Management, Nicolas Castilla
– Greenhouse Operation and Management, Paul V. Nelson
– Soilless Culture, Michael Raviv & J. Heinrich Leith
– Growing Media for Ornamental Plants and Turf, Kevin Handreck & Niel
Black
– Plant Nutrition of Greenhouse Crops, Cees Sonneveld & Wim Voogt
– Hydroponic Food Production, Howard M. Resh
– Tomatoes, Eb Heuvelink
Trade shows and conferences
– Great Lakes Fruit, Vegetable and Farm Market Expo & Michigan Greenhouse Growers Expo – Dec 4-6, 2018, Grand Rapids MI
– Indiana Horticulture Congress, Feb 12-14, 2019, Indianapolis IN
– Indiana Small Farm Conference, Feb 28 – March 2, 2019, Danville IN
– Indoor Ag Con, April 17-19, 2019, Las Vegas NV
– Cultivate’19, July 13-16, 2019, Columbus OH
Manufacturers and distributors (list is not complete but it’s a good start):
– http://www.tunnelberries.org/single-bay-high-tunnel- manufacturers.html
– http://www.tunnelberries.org/multi-bay-high-tunnel- manufacturers.html
USDA NRCS Indiana EQIP Grant
– https://www.nrcs.usda.gov/wps/portal/nrcs/main/in/pr ograms/financial/eqip/
– https://www.nrcs.usda.gov/wps/portal/nrcs/detail/in/technical/ecoscience/bio/?cid=nrcs144p2_068639
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