The large amount of capital investments in greenhouse construction poses especially acutely the question of the date of their repayment.
At a fixed amount of capital investments per unit of area under glass this date is a function of the net income.
As is wellknown, the size of the net income of any producing enterprise is the result of the influence of two groups of varying factors - volume and structure of production on the one hand and net income per unit of product on the other hand.
The question concerning the optimal structure of greenhouse growing of vegetables is reduced to the answer to two questions: what to produce and when to produce it.
At various dates of planting and receipts of produce, one and the same crop, for example tomatoes, may have several different production lines - early, mid-season and late - fully differentiated from the agro-technical and economic points of view.
The separate types of production may take up the areas either throughout the entire production period or only during a part of it.
From the standpoint of the objectives of this elaboration, the occupation of the areas in the course of an annual production period will be designated as a scheme.
Two kinds of schemes are thus outlined - annual, when the areas are taken up by a single production, and combined - i.e. composed of two or more productions.
The solution of the task so assigned are sought in two successive stages:
- Developing methods for ascertainment, analysis and economic evaluation not only of the schemes adopted in production, but also of all agrotechnically admissible and economically expedient schemes at a definite stage.
The methods are illustrated by a concrete elaboration for the conditions prevailing in 1966–1967.
- Drawing up an economic-mathematical model for the optimal structure of greenhouse vegetable growing.
Based on this, a concrete task is solved with the aid of computers.
The established schemes are used as initial information.
The elaboration is prepared for an area under glass of 240 ha.
The data are supplied by the Greenhouse State Economic Enterprise, the Pazardjik branch, and by the Central Board of the enterprise.
The combined schemes envisage three dates of liquidating the first crops - 10 January, 30 January and 28 February.
The planting of the second crops at a permanent place is carried out 10 days later - at 20 January, 10 February and 10 March respectively.
The differences in the dates are quite sufficient for forming the separate productions and for delineating their agrotechnical and economic indicators.
The liquidation of the annual schemes and of the second crops of the combined schemes is visualized for the period of 20 June-30 July.