The Moldavian Scientific Research Institute for Irrigated Farming and Vegetable Growing has conducted experiments for raising vegetable crops in electric heated hotbeds.
The heating element used was a galvanized steel wire of a diameter of 2.57 mm, inserted in ceramic pipes of a diameter of 6 cm and length of 35 cm, placed in the hotbed soil to a depth of 30–35 cm.
The pipes were laid in three rows lengthwise of the hotbed.
The voltage was 220 V, and the power 200 Watts per square meter.
Forcing of onions for use in green stage was conducted at the end of January.
Selected bulbs of the onion cultivar Grubnenski were used for forcing.
The hotbeds were heated mostly during the night.
The soil temperature during forcing ranged from 18 to 24°C and the air temperature from 12 to 18°C. The mass appearance of leaves commenced on the 4–5th day after planting.
Forcing lasted for 20–22 days on planting in January and 13–15 days on planting in March (table 1).
The considerable acceleration of forcing in March is to be explained by the improved light and temperature regimes.
Decrease in the electrical energy input and in the yield was observed with the acceleration of onion forcing which can be explained by the rise in temperature.
The investigation results warrant the inference that onions for use in green stage can be grown in electrically heated hotbeds prior to planting early tomatoes, peppers and eggplants.
Onion forcing can also be carried out in hotbeds intended for pricking out early tomato seedlings.
The comparative study of onion cultivars for forcing shows the advantage of the Challot species.
The yield of green onions of these cultivars is 1.2 to 1.6 times as great as the weight of the planted bulbs.
Lettuce growing. The experiments were made with the cultivars Maiska 692, Byotnerova, Moskovska parnikova.
Planting was carried out every 15 days beginning with 1 September.
The number of days to picking is 86–124 on sowing in November-December, 60–40 in February-March and 35–45 in April.
The yield per sqm was 1, 1.4, 2.2 kg resp.
The reason for the low yield in the winter is the shortened day and the decrease in light.
The inference from the conducted investigation is that the sowing of lettuce for consumption in the winter-spring season in electric-heated hotbeds can be carried out from September to April.
Lettuce, sown in September, is ready for picking in November; on sowing in October: in November, on sowing in December: in January; the January-February sowing produces crop ready for picking in March-April.
Radishes growing. The Rubin cultivar was sown every 15 days beginning with 15 August.
Experiments conducted on heated soil and automatic temperature regulation show that highest yield of radishes is obtained at a soil temperature.