Effects of a special solar collector greenhouse on water balance, fruit quantity and fruit quality of tomatoes

• Improvement of fruit quantity and quality caused by a solar collector greenhouse.
• The passively cooled system can be used to increase the water use efficiency.
• The solar collector greenhouse contributes to fresh water-saving.
• Condensate-containing nutrient solution can be reused for hydroponic systems.
• Zn supplementation resulted in higher contents of health-promoting plant compounds.

Based on the fact that several regions worldwide and even in Germany are affected by water deficit problems, a new agronomic approach was developed to produce tomatoes (Solanum lycopersicum L.) in a sustainable way. The main objective of this study was to investigate the effects of a special solar collector greenhouse consisting of finned tube heat exchangers on the quantity and quality of fruit, water use efficiency and water balance. Changing microclimatic conditions in this system positively affected plant physiological processes, resulting in an increased total yield of up to 31.8% and a decreased total water uptake within the crop of up to 29% when compared with a commercial greenhouse. These conditions led not only to a reduction in the amount of nutrient solution (NS) consisting of valuable fresh water but also to increased water use efficiency (+81%). Furthermore, it was found that the finned tube heat exchangers can be considered as a complex water management system, which can be used to collect high quantities of condensation water. It was calculated that a fresh water supplementation used to mix the NS can be completely omitted when the captured rain and condensation water is reused under the conditions in the solar collector greenhouse. In order to test to what extent the collected condensation water was suitable for irrigation, the effects of condensate-containing NS with a higher Zn concentration (1.74 mg L−1) were examined regarding yield and the ingredients in tomatoes. Compared with an applied NS supplemented with 0.2 mg Zn L−1, condensate-containing NS increased fruit quantity (+39%) and quality, e.g., contents of lycopene (+15%), β-carotene (+13%) and phenolic compounds (+12%). Based on the above-mentioned results, it was concluded that a collector greenhouse can be regarded as a useful tool to increase the yield as well as to reduce amounts of fresh water, and the condensation water can safely be reused in hydroponic systems.