Nutrients
https://www.project-springtime.org/research/nutrients/
General
- Required composition of minerals differs from that for soils
- Most important: composition in water can change very rapidly eg. because of selective uptake by plants
- Concentration should be between 1000 and 2500 ppm
About the water
Cornell strongly recommends to start with water analysis.
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Alkalinity, reported as units of Calcium Carbonate equivalents CaCO3. 0 to 300 ppm is common. More important value than pH.
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“Depending on your alkalinity, you may need to choose a fertilizer formulation with a greater proportion of acidic nitrogen forms (ammonium or urea) or add acid to neutralize the alkalinity and counter the pH rise.”
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“Often linked with your water alkalinity are considerable levels of Ca, Mg and S in the water”, also Sodium and chloride and compensate with fertilizer.
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Electrical conductivity (EC), should ideally beless than 0.25 mS/cm for closed systems.
Needed nutrients
Macronutrients
- nitrogen
- phosphorus
- potassium
- sulfur
- calcium
- magnesium
Micronutrients
- iron
- manganese
- zinc
- boron
- copper
- molybdenum
- chloride
- nickel
Chloride and nickel aren’t included in most recipes, as they’re available in sufficient quantities as impurities.
Plant types
For vegetative crops, most nutrient-solution recipes don’t adjust the ratio of nutrients while they grow; whereas, in fruiting crops the ratio may be adjusted to alter the shift between vegetative and reproductive growth.
- 150ppm N works well for head and leaf lettuce during the main production stage;
- 175 to 200ppm N is more appropriate for kale, Swiss chard and mustard greens, which tend to be slightly heavier feeders.
- During seedling propagation a some-what lower fertilizer target of 125ppm N works well for both
- tomato and other fruiting crops have higher nutrient demands than leafy greens: higher nitrogen, potassium, calcium and magnesium
Plant stages
- vegetative growth: high in nitrogen, calcium and magnesium
- flowering: high in potassium and phosphorus
- nitrogen restriction inhibits vegetative growth and helps induce flowering.
Recipies
- http://www.greenhouse.cornell.edu/crops/factsheets/hydroponic-recipes.pdf
- https://cals.arizona.edu/hydroponictomatoes/nutritio.htm
Symptoms of nutrient deficiencies
- Nice table: https://www.hydroponics.net/learn/nutrient_deficiencies.php (copied to this site here for easier printing)
- Description: https://www.hydroponics.net/learn/deficiency_by_element.php
- https://cals.arizona.edu/hydroponictomatoes/nutritio.htm
Improving nutrient uptake
To improve nutrient uptake:
- chelating agents can be added
- humic substances (Note: science seems to know very little about humic substances. They are complex molecules apparently created during dead plant breakdown, which help with plant growth “substantially” according to some studies)
Mixing
- Use stock tanks to avoid a nasty precipitate or sludge that will occur when specific nutrients are mixed in the concentrated form (e.g. calcium can combine with phosphates and sulfates to form insoluble precipitates)