During a period of several years experiments were carried out for studying the effect of different temperatures of the nutritive solution and the substratum on the growth and development of seedlings and full-grown plants of different cucumber varieties.
The temperature of the nutritive solution was maintained by an automatic system with an allowance of ± 1°C. The registration of the parametres of the greenhouse substratum was also carried out by a special automatic semi-conductor system.
The following cucumber varieties were included in the experiments: 'Mnogoplodnii - VSRV', 'Spot-resisting' and 'Din-ZO-SN'. The growth, development and yields of the plants were controlled according to the generally adopted methods.
The basic results of these experiments are explained in our present report.
It was established that there exists an optimum temperature of the nutritive solution under the specifically combined conditions.
At this temperature the development of the seedlings was best and their quality proved to be the highest possible (fig. 1).
At a temperature of +35°C of the nutritive solution the growth of the assimilative apparatus and the root system was most vigorous, and the absorbing surface of the roots was greatest.
With the rise or drop of temperature the quality of the seedlings was deteriorated.
It was observed that in early phases the plants reacted to a lesser extent to the decrease or increase in the temperature of the nutritive solution than during the later phases.
The optimum temperature of the nutritive solution depends on the combination of the air temperature and the light intensity in greenhouses.
Under summer crop conditions - high average day temperatures (+28°, +30°C) with maximum day temperatures (+33, +35°C) and maximum sunlight - the optimum temperature of the nutritive solution was +15°C. Under conditions of decreased light intensity - spring crops - the optimum temperature of the nutritive solution was around +25°C.
The cucumber varieties differ to a considerable degree in respect to the temperature of the nutritive solution.
The growth and development of the Spotresisting variety proceeded best in the conditions of slightly lower temperature of the nutritive solution, as compared to the 'Mnogoplodnii VSHV' variety (table 1).
The Chinese variety 'Din-zo-sn' develops equally well in a rather wide range of temperatures of the nutritive solution.
During the experiments a tendency was remarked towards an increase of the yields when the temperature of the nutritive solutions decreased during the night hours (table 2), the fruit-bearing period lasting 42 days.