TEMPERATURE CHARACTERISTICS AND BOWEN-RAT IO IN POTATO STANDS AT VARIOUS IRRIGATION REGIMES

In conditions of vegetation hall with open sides and glass roof lettin g ultraviolet radiation in and with lysimeters of an area 6.25 m(2) an d depth of 1.40 m with a possibility to adjust height of the groundwat er table (GWT) at the experimental station of the Research Institute o f Soil and Water Conservation at Horin near Melnik, in 1992 in potato stands gradually in different phases of development surface temperatur es of leaves were measured by touchless sensor, air temperatures and a ir humidity over the stand and at a height of 2 m. Data were used for evaluation of the effect of moisture regimes of soil, formed under the hall by underground trickle irrigation (section A), surface trickle i rrigation (section B), sprinkling (section C) and dispersion irrigatio n (section D). The following lysimeters were used in the trials: lysim eters L3 and L11 (without GWT), L12 and L13 (GWT 0.8 m), L14 (GWT 0.40 m) and finally, L10 (without stand and without GWT). Measurements wer e carried out in two-hours' intervals from 7 a.m. to 5 p.m. of summer time during a day gradually in different developmental stages througho ut the whole vegetation period. The values taken were plotted in graph s, including calculated values of the Bowen ratio and fraction 1/(1 beta) which for identical time, that is at the same solar radiation wh ich then becomes a constant, gives comparable values for studied treat ments of irrigation regime, making possible to judge the differences i n the levels of actual evapotranspiration. Except graphic processing f or visual comparison the data were subject to straight line regression analysis, searching for relationships between surface temperature of plants, temperature, moisture and tension of water vapour in the air o ver the stand. In another analysis the corresponding factors of treatm ents were compared with chosen standards (sections A and L3). This res ults in finding of the dependence of surface temperature of plants on air temperature over the stand and in addition, on tension of water va pour for hall and more significantly (at r > 0.66) for lysimeters. Pra ctically no dependences on surface temperatures and Bowen ratio for ha ll were found. Correlation coefficient for lysimeters r ranged from 0. 125 to 0.302. The suitability of measurements of surface temperatures for judging of state of plants in various irrigation regimes can be co nfirmed. The use of the Bowen ratio for distinction of effects of wate r regime of soil is not unambiguous for vegetation hall. Better result s were acquired from observation with lysimeters.