RESULTS OF HYDROPONIC GROWING OF CUCUMBERS IN KOUBAN
Hydroponic growing of vegetable crops in greenhouses has been practised for the last 7–8 years. Since 1965 research workers of the Chair for Vegetable Growing at the Kouban Institute of Agriculture have been studying the effectiveness of vegetable growing on different substrata. A hydroponic greenhouse has been used for growing the seedlings; 3 others have served for growing the vegetables (in troughs). The nutritive solution is poured over automatically, at regular intervals. The area of each one of these greenhouses is 1000 m2.
The substrata consist of river gravel, crushed stone and keramsite. The substrata are treated with 1–5% solution of sulphuric acid or super-phosphate before transplanting the seedlings. Best results are obtained, however, when river gravel is treated with sulphuric acid, and keramsite with a superphosphate solution. Thus, the yield of tomatoes, grown in keramsite treated with a superphosphate solution, has been 22 per cent higher, as compared to yields of tomatoes, grown on keramsite, treated with sulphuric acid.
During the past few years we have experimented with the following substrata: keramsite of a 3–20 mm dia.; gravel of a 3–15 mm dia.; vermiculite, as well as vermiculite with an admixture of gravel and keramsite. Some of the physical properties of the substrata are given in table 1.
Our observations have shown that plants develop best over keramsite of high water-holding capacity and higher thermal capacity (the temperature of a 10 cm keramsite layer, where the roots of the plants are treated, is by 2–3°C lower than that of a gravel one). This property is very important for eliminating overheating of substrate during the spring-summer period. The plants develop more weakly on gravel than on keramsite, but better than on soil.
The better development of the plants on artificial substrata can be explained partly by the high water content of their tissues, demonstrated through the suction capacity of their cells. In plants cultivated on soil it is 1.8, in those on gravel 0.9, and on keramsite 0.12 atmospheres.
During the winter-spring period the vermiculite has shown unsatisfactory results. The percentage of plants that have died is very great, due to the strongly developed root-decay. That is why this substratum has not been used in further experiments.
The yields up to 1 July 1967, and the beginning of the harvesting period