Basic calculations to make your own hydroponics nutrients
Reference Rates for leafy greens:
Howard Resh |
Observed Rates |
Cornell | UA CEAC | |
N | 165-200 | 125-200 | 210 | 189 |
P | 50 | 15-90 | 31 | 39 |
K | 150-210 | 80-350 | 235 | 341 |
Ca | 150-200 | 38-220 | 200 | 170 |
Mg | 40-60 | 14-96 | 49 | 48 |
S | 64 | |||
Fe | 5 | 1-10 | 4 | 2 |
Mn | 0.5 | 0.25-1 | 0.5 | 0.55 |
Zn | 0.05-0.15 | 0.1-2.5 | 0.1 | 0.33 |
B | 0.3-0.5 | 0.14-1.5 | 0.5 | 0.28 |
Cu | 0.03-0.15 | 0.023-0.13 | 0.1 | 0.05 |
Mo | 0.02-0.05 | 0.024-0.075 | 0.01 | 0.05 |
To convert P2O5 to P, multiply by 0.4364
To convert P to P2O5, multiply by 2.2915
To convert K2O to K, multiply by 0.8301
To convert K to K2O, multiply by 1.2047
For Example,
Potassium sulphate (0-0-50)
P in potassium sulphate : 50 * 0.8301 = 41.5%
Choice of fertilizers:
You can use any fertilizers of your choice like 19-19-19 or ammonium nitrate, or any other water-soluble fertilizers. I am using these because they are cheap and easy to get. Below values may change when you change the brand.
Calcium Nitrate: Ca: 18.8%, N: 15.5%
Potassium Nitrate: 13-0-45 (13% N, 37.3% K)
Magnesium Sulphate: Mg:10%
Potassium Sulphate: 0-0-50 (41.5% P)
Monopotassium phosphate: 0-52-34 (22.7% P, 28.7% K)
Fe EDTA 18%
Micronutrient Mix: As per label
Desired PPM Quantity:
N: 200 ppm P: 50 ppm K: 300 ppm
Ca: 200 ppm Mg: 50 ppm Fe: 5 ppm
Mn: 0.8 ppm Cu: 0.07 ppm Zn: 0.1 ppm
B: 0.3 ppm Mo: 0.03 ppm
You can test your water source and alter the above values accordingly.
Calculations to achieve desired PPM quantity with available choices:
Ca: 200ppm
Wt. of Calcium nitrate = Required Ca / Available % in fertilizer
= 200 PPM / 18.8%
= 200 / (18.8/100)
= 200 / 0.188
= 1063.8 PPM
= 1000 mg (Approx.)
= 1 gm
Weight of Calcium Nitrate: 1 gm/L
Fertilizer salts provide two ions. Let us calculate the ppm (or mg/L) of nitrogen supplied using 1000mg of calcium nitrate in 1 L of water. This is calculated by multiplying the total mg/L of fertilizer salt used by the percent nitrogen. (15.5% N)
N in added Calcium Nitrate: 1000 * 0.155 = 155 PPM
Calcium nitrate provides 155ppm Out of 200ppm of N required.
N Remaining = 200 – 155 = 45ppm
N: 45ppm
Wt. of Potassium Nitrate 13-0-45 = Required N / Available % in fertilizer
= 45 PPM / 13%
= 45 / 0.13
= 346.15 ppm
= 0.35 gm/L
Weight of Potassium Nitrate: 0.35 gm/L
K in added Potassium Nitrate: 346 * 0.373 = 129 PPM
Potassium Nitrate provides 129 ppm Out of 300ppm of K required.
K Remaining = 300 – 129 = 171ppm
P: 50ppm
Wt. of Monopotassium phosphate (0-52-34) = Required P / Available % in fertilizer
= 50 PPM / 22.7%
= 50 / 0.227
= 220.26 ppm
= 0.22 gm/L
Weight of Monopotassium phosphate: 0.22 gm/L
K in added Monopotassium phosphate: 220 * 0.287 = 63.14 PPM
Monopotassium phosphate provides 63 ppm Out of 300ppm of K required.
K Remaining = 171-63 = 108ppm
K: 108ppm
Wt. of Potassium Sulphate (0-0-50) = Required K / Available % in fertilizer
= 108 PPM / 41.5%
= 108 / 0.415
= 260.2 ppm
= 0.26 gm/L
Weight of Potassium Sulphate: 0.26 gm/L
Mg: 50ppm
Wt. of Magnesium Sulphate (10% Mg) = Required Mg / Available % in fertilizer
= 50 PPM / 10%
= 50 / 0.1
= 500 ppm
= 0.5 gm/L
Weight of Magnesium Sulphate: 0.5 gm/L
We will use a micronutrient mix to provide all micronutrients. We will use FeEDTA (13% iron) because the micronutrient mix contains Fe at low levels. Out of 5ppm required, Fe EDTA will provide 4ppm Fe.
Fe: 4pmm
Wt. of FeEDTA (13%) = Required Fe / Available % in fertilizer
= 4 PPM / 13%
= 4 / 0.13
= 30.7 ppm
= 0.03 gm/L
Weight of FeEDTA: 0.03 gm/L
1. Total Fertilizer Weights to make 1L of nutrients solution:
Weight of Calcium Nitrate: 1 gm/L
Weight of Potassium Nitrate: 0.35 gm/L
Weight of Monopotassium phosphate: 0.22 gm/L
Weight of Potassium Sulphate: 0.26 gm/L
Weight of Magnesium Sulphate: 0.5 gm/L Weight of FeEDTA: 0.03 gm/L
Weight of Micronutrients: As per the label
2. To make a volume of nutrients solution, multiply water volume to above weights. Total Fertilizer Weights to make 1000L of nutrients solution:
Weight of Calcium Nitrate: 1000 gm/L
Weight of Potassium Nitrate: 350 gm/L
Weight of Monopotassium phosphate: 220 gm/L
Weight of Potassium Sulphate: 260 gm/L
Weight of Magnesium Sulphate: 500 gm/L Weight of FeEDTA: 30 gm/L
Weight of Micronutrients: As per the label
3. To make stock solutions, check solubility of salts:
All salts are within soluble values.
We will put all nitrates in Stock A and phosphates and sulphates in Stock B.
To make 200x of stock solution for 10L Volume,
Stock A
Weight of Calcium Nitrate: 1 gm/L*200*10 = 2kg
Weight of Potassium Nitrate: 0.35 gm/L *200*10 = 700gm
Weight of FeEDTA: 0.03 gm/L * 200 * 10 = 60gm
Stock B
Weight of Monopotassium phosphate: 0.22 gm/L * 200 *10 = 440gm
Weight of Potassium Sulphate: 0.26 gm/L * 200 * 10 = 520gm
Weight of Magnesium Sulphate: 0.5 gm/L * 200 * 10 = 1kg
Weight of Micronutrients: As per the label * 200 * 10
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