Tomatoes Guide values

The following reference values are taken from a master's thesis at the University of Applied Sciences Südwestfalen. See link below.

Fertilization of tomatoes in substrate cultures is often based on values given in mmol/l. To make them easier to understand, the reference values have also been converted to g/l. The following table provides an overview of the requirements for anions, cations, and trace elements for tomatoes.

Examples of how to convert mol to grams and vice versa can be found here.

In general, the cultivation of tomatoes as substrate cultures is carried out as follows:

- Starting seedlings in December/January

- Grafting the seedlings:
   - Topping after the 3rd leaf → 1 seed = 2 shoots (saving seed costs)
   - Possibly topping again after the 6th leaf

- Shoots bearing tomatoes are harvested continuously

- Approximately 30 harvests per year

- Harvest per plant: 600 g tomatoes
   - 600 g x 2.5 plants/m² x 30 harvests = 45 kg tomatoes / m²
   - For a 20 m² greenhouse: 900 kg tomato harvest / annual yield

The following points must be observed when fertilizing tomatoes in substrate cultures:

- In general, an A and B solution must be prepared for the nutrients.

- Both solutions must not be added to the water at the same time, as this can lead to gypsum formation or precipitation (high calcium content).

- Fertilizer application is generally based on irradiance values (LUX):
   - 20 to 30 starts during high solar radiation in summer, e.g. 100 cm³/plant at approx. 20 kg
   - 2 to 3 starts during darkness (February/March)

- During the start phase, tomatoes require 50 cm³/plant every 8 hours

- Otherwise 3 to 5 l/plant during the main growth phase

- A high salt content is necessary for flavor
   - If the tomato plants are not bearing fruit, less potassium should be applied

- Ammonium is only added to stabilize the pH value in the growing medium

- Potassium and calcium should be present in a 1:1 ratio in the growing medium or drain water

- When cultivating with a closed system, 8 mmol K and 4 to 5 mmol Ca are recommended for the nutrient solution

- Sulfur levels in the nutrient solution can be reduced to 2 mmol.

- In tomato cultures, adjustments are made according to the developmental stage of the crop (see table below):

Fertilization costs:

1,300 l of water per m² / year are required (of which 300 l can be recycled as process water)
this corresponds to 1.3 m³ water/m²

1 m³ water = €0.30 - €1.00
the following values are assumed for the nutrient solution:
Fertilizer price per m³ water = €1.00 - €1.20

Converted to 2.5 plants per m², this results in fertilization costs of approx. €1.70 to €2.90 per m² / year.
For an exact fertilizer requirement calculation, a program can be used, which is linked below:
http://www.haifagroup.com/Dutch/knowledge_center/expert_sofwares/

Systems
There are various hydroponic systems that must be selected individually according to different criteria. Which crop(s) are to be grown, what financial resources are available, and how much labor time can or should be invested? For combining a system with aquaculture, NFT or ebb and flow are particularly suitable due to their simple structure and a separate area for the nutrient solution.

Process water
The feed composition provides the basis for estimating the theoretical water load and the nutrients available for hydroponics. However, the amounts of nutrients that accumulate are variable and depend on the feed composition (crude protein content), feeding intensity, stocking densities (kg/m³), and the distribution of feeding intervals throughout the day. By feeding over 24 hours, fluctuations in water load can be reduced, enabling a more uniform water flow/water exchange.
The total ammonium nitrogen production consists of 51.3% of the N/kg feed as non-fecal losses and 9.4% of the N/kg feed as fecal losses. The remaining 39.3% of the N/kg feed is used for fish growth. The aim of the model calculation is to calculate as precisely as possible the amount of nitrate (g) in the water at different fish stocking densities in order to estimate the nitrogen quantities. For this purpose, various factors were incorporated and used as variables in a table. At a feeding intensity of 3%, this results in a fattening period of 147 days. In particular, an intensive stocking density (450 kg/1.5 m³) produces very high nitrate quantities, while a low stocking density (75 kg/1.5 m³) does not come close to producing this amount. This means that nitrate quantities vary considerably.

Nutrient supply

Fertilization in hydroponic cultures is based on reference values for specific salt concentrations in the water. These salt concentrations are described by the EC value (electrical conductivity). An EC value of 3.7 is a representative reference value on average, and nutrients are calculated accordingly. Nutrient addition is carried out in two steps, A and B solution, which prevents clumping (gypsum formation) of the nutrient solution. The nutrient quantity is adjusted according to the plant's stage of development. On average, the nutrient solution volume is 3-5 l per plant during the main growth phase.

Conclusion:

I) Plants
Nitrate requirement: 1.426 g/l NO3
Plant quantity: 5 l/plant
Number of plants: 2.5 plants/m²
Total area: 20 m²
Calculation (1): 1.426 g/l NO₃ * 5 l/plant * 2.5 plants/m² * 20 m² = 356.5 g NO₃/year and total area

II) Process water
Assumption: 75 kg/tank
Nitrate quantity: 312.14 g from three tanks
Fattening days: 147
Cycles: 365 ÷ 147 = 2.5
Calculation (2): 2.5 cycles * 312.14 g NO3/year and total area = 780.35 g NO3/year
Calculation (3): 780.35 g NO3/year ÷ 356.5 g NO3/year and total area = 2.19

At a stocking density of 75 kg/tank, 2.19 times more nitrate is currently available than the tomatoes require.

III) Recommendation:
Calculation (4): 75 kg/tank ÷ 2.19 = 34.25 ~ 34 kg/stocking density
For the required nitrate quantity of the plants over a total area of 20 m², a fish stocking density of 34 kg is recommended.

Source: https://www.fh-swf.de/media/neu_np/fb_aw_2/dozentinnen/professorinnen_2/lorleberg/projekte_masterstudiengang/Report_Planung_Aquaponik-Demonstrationsanlage_2015.pdf