Greenhouse soil is subjected to intensive cultivation, watering and great mechanic pressure.
Micro-aggregates increase under the annual action of these factors while the share of the macro-aggregates in the soil diminishes.
This results in progressive negative alterations in a large part of its properties.
In the absence of respective measures some of the changes may become a factor limiting fertility.
The micro-aggregate soil for example has a more compact structure than the macro-aggregate soil.
The more compact soil, beyond the limits of the optimum for a given plant species, as well as the more firable one, adversely affect the plant organism and lead to negative consequences.
The objective of this investigation is to establish the influence of soil compaction on tomato growth and development.
We conducted pot experiments with artificial monoliths in the Sofia greenhouses of the Institute of Genetics and Plant Breeding during the period of 1966–1968. The material used in the experiments was soil taken from the 0–40 cm layer of a greenhouse operating for ten years in Dimitrovgrad.
It was 33.4 per cent physical clay, 2.51 specific gravity, 6.75 pH and 4.48 per cent humus.
Use was made of Wagner pots and pots-pipes made of polyvenyl-chloride of the size of: inner diameter 152 mm, height 400 and 600 mm.
We modelled in the pipes subsoil of a compaction of 1.1, 1.2, 1.3, 1.4, and 1.5 g/ccm and a soil of the same compaction (1.1 g/ccm) of a thickness of 100 and 150 mm.
The water in the pipes was provided by means of a constant water table, 340 and 520 mm from the surface of the monoliths.
Homogeneous monoliths were created in the Wagner pots, having the compaction indicated for the "subsoil" and a height of 200 mm.
The water in them was supplied by weight.
In some of the pots it was maintained within the limits of the field capacity at a water-filled pores/air ration of 1:0.67 in the most friable structure to 1:0.25 in the most compact structure, and in others, by filling with water 70 per cent pores of the total soil porosity, at a water-filled pores/air ratio of 1:0.43. One plant of the Moneydor cultivar in the phase budding of the first inflorescence was planted in each pot in the manner adapted in greenhouse practice.
The studies showed that the capillary rise of the water in the pipe experiments did not ensure normal water supply to the plants under the conditions prevailing in the Sofia region during the test years.
The translocation of the water to the upper layers of the monoliths was the poorer the drier and warmer the air, the more intensive the growth and transpiration of the plants and the more compact the "subsoil". The plants in the more compact "subsoil" began to wither earlier and in the course of a longer period than those in the more friable one.
Size and other differences between the plants of the different variants occurred during the