The natural conditions in this country make it possible to produce the basic amount of vegetables in the open.
In 1968 the acreage of vegetable crops grown in the open was 899 500 hectares, the transplanted crops accounting for 61 per cent.
Altogether 2700 hectares of hotbeds or 58 per cent of the total covered area were utilized in 1968 to ensure the supply of the open areas with seedlings.
In 1968 1300 hectares of poly-ethylene plant growing structures were used in this country and 475 hectares of glass greenhouses.
Single slope hotbeds, with a pit and manure heated, were mostly used in seedling production during the spring and summer periods.
At present extensive construction of electrically heated hotbeds is under way especially in the southern regions of the country.
There exists in this country a discrepancy between the mechanization of production in the open and the technology of seedling production in such obsolescent plant growing structures as the hotbeds.
The scientific research work and the practice of the foremost farms show that under the conditions prevailing in the central regions of the USSR, the use of polyethylene cover and solar heating permit to solve the problem of supplying seedlings for midseason field production.
The polyethylene plant growing structures for raising early seedlings should be supplied with additional technical heating.
The farms in the Moscow and Leningrad regions, in the Ukrainian, Moldovian and Kazakhstan republics have gained experience in raising seedlings in such plant growing structures.
The Latvian Scientific Research Institute for Agriculture has worked out a design for light wooden structures for block polyethylene greenhouses.
The design is characterized by the absence of a framework, beams and rough columns; it is further distinguished by the simple and easy fastening of the large-sized polyethylene films with the aid of special stretching devices.
The Leningrad Agrophysical Scientific Research Institute has worked out an airproof greenhouse on the basis of stabilized polyethylene which is now undergoing production testing.
The joint research of the Institute of Chemical Industry and the Institute of Agriculture resulted in the elaboration of new kinds of polymer light transenscent materials: stabilized polyethylene film with antistatic additives, polyvenylchloride film for use in farming and reinforced material - glass plastic.
The adoption of these new materials in the construction of plant growing structures will allow a considerable extension of the period of their exploitation.
The experience of the collective and state farms in this country gained in the construction and exploitation of polyethylene greenhouses shows high economic effectiveness in growing vegetable crops and seedlings in