**2.1 Substrate culture**

Hydroponic systems in a small amount of substrate (3 to 15 l per plant) filled in containers, bags, slabs or channels. Slabs of rockwool, peat or coconut fiber are used. This system is combined with different types of trickle irrigation. There are 'open systems' in which the drainwater flows out of the substrate slabs or cultivation container in the ground. Preferable used are the 'closed systems' in which the growing medium is lying in channels and the nutrient solution is recirculating.

#### **2.2 Water culture**

The plants are cultivated without any substrate, except the substrate for propagation of the young plants. The plants are staying or hanging also in channels in recirculating nutrient solution. Quite known systems are the 'Nutrient-Film-Techniques' (NFT) and the 'Deep-Flow-Techniques' (DFT). Also gravel culture can be grouped belong to the water culture, because the gravel has only the function to stabilize the root system.

#### **2.3 Aeroponics**

The plants are cultivated without any substrate and staying or hanging on plastic-foam-sheets and the root system is hanging in a closed space. The nutrient solution is given by very fine nozzles as a kind of fog-system. Important is a high frequency of spraying with nutrient solution, advisably to spray every 2 to 4 minutes for 20 to 30 seconds according to the developmental stage of plants. This system is rarely used for cucumber cultivation.

#### **2.4 Aquaponics**

Is a combination of aquaculture with typical fish keeping in ponds and the water culture system 'nutrient-film-technique' (NFT) as a closed aquaponics, where the plants were fertilized only with the fish water. This technique becomes more and more important for the food production and has an increasing popularity, even though the system is not methodologically sound and completely scientifically investigated. Nowadays, this system is mainly used to cultivate tomatoes and leafy vegetables [4] it can be used also for cucumber cultivation.
