Hotbed bioclimate changes very rapidly.
This peculiarity is determined by the design of the hotbed, its exposure, method of heating, shading, ventilation.
Our previous studies showed that the hotbed microclimate also changes depending on the amount of manure and the time of its application.
The changes in the meteorological elements, however, are not the same for all points in the area under cover.
In the course of 3 years (1963–1966) we studied the dispersion of hotbed microclimate and how it affects the development and weight of head lettuce (Lactuca sativa var. capitata).
The alterations were followed up of solar radiation, light intensity, air and soil temperature, soil moisture, and shadow configuration in manure-heated hotbeds with different depth of manure layer and a cold frame, 8 m long and incline of the slope 12 per cent to the south.
The scheme for the layout of the instruments in the hotbed is shown on fig. 1.
The change in the bioclimate conditions in a hotbed, heated by a thin layer of manure, most popular in this country and economically most advantageous, is discussed in greater detail.
The conducted investigations show that dispersion occurs first of all in the intensity of solar radiation, which acquires different values in the various parts of the hotbed.
If the intensity of solar radiation in the middle of the hotbed is designated by 100 per cent, along the northern side it rises to 102 per cent on the average, and along the southern one it drops to 83 per cent.
The intensity of the cumulative solar radiation in the central part of the hotbed amounts to 0.595 cal/cm2/min, along the northern side to 0.606 cal/cm2/min, and along the southern one to 0.493 cal/cm2/min on all sunny days during the growing season.
The central and northern strips of the hotbed receive more direct solar radiation and the southern one more diffuse solar radiation.
Therefore, 3 microclimatic strips are differentiated in the hotbed with respect to solar radiation intensity - along the southern and the northern sides of a mean width of 40 and 20 cm resp. and a central one of 80 cm.
Fig. 2 presents the day course of the intensity of cumulative solar radiation in the hotbed on 13 April 1966. It is readily seen that the shadow thrown by the southern side is strongly reduced, the regularity pointed out is maintained.
The solar radiation intensity in the northern strip of the hotbed is higher than in the centra by 0.026 cal/cm2/min. and by 0.153 cal/cm2/min than in the southern end of the hotbed.
Those differences are presented in fig. 3.
Dispersion in solar radiation intensity occurs also longitudinally in the hotbed.
During the day it has greater values in the forenoon.
The western frame receives on the average about 7 per cent more calories than the