The state of heat resources and yield dynamics of the field crops in the conditions of the northern Steps of Ukraine
Authors: Chaban V. I. , Kliavzo S. P. , Podobed O. U. , Horbatenko A. І. 
Published: July 2021

The most important environmental factors for the environment and habitat of plants include temperature. Agro-industrial production requires up-to-date information on the state of thermal resources and the response of plants to global warming within each region. The purpose of the research is to evaluate the state of thermal resources and the dynamics of crop yields in the Northern Steppe of Ukraine. Material for the research was the results of observations of the temperature regime of the AISW Dnipro (1961–1990 and 1991–2018) and data of winter wheat, spring barley, corn, sunflower in stationary experiments on control variants (DPDG “Dnipro”). Statistical data were used to evaluate the data by period: arithmetic mean (M); standard deviation (S); confidence interval (CL0.05) probability (P); repeatability (P × 100 %). Statistical processing was performed using applications in Excel 2003 and Statistica (version 6). Analysis of the thermal regime data showed that in 1991–2018, the average temperature for the year increased by 1.0 °C compared to the climatic norm (1961–1990), by 0.9 °C during the warm and cold periods. vegetation period of early cereals and late crops – by 0.8–1.0 °С. The average rate of increase in the average annual temperature in 1961–2018 was 0.31 ° C/10 years. Between 1991 and 2018, there were 15 cases with temperatures above 9.5 °C, with a recurrence rate of up to 53 %. The last decade (2009–2018) is characterized by a further increase in temperature during the year – by 1.5 ° C, the vegetation of early cere-als – by 1.6 °C, and late crops – by 2.0 °C. It is established that the warming is due to the temperature increase in the cold season – in January, February and March by 1.1,71.7 °C. Positive anomalies occur in July and August (+1.5 ° C). For estimating thermal resources, the important characteristics are the average temperature of the coldest and warmest months of the year. January 10-year average temperatures steadily increased from (-6.5) °C in 1961–1970, to (-4.0) °C in 2011–2018. Their annual variability decreased. The recurrence of high temperature (> -5 °C) in January increased from 34–35 % in 1961–1980 to 73 % in 2011–2018. The average values of July temperatures for 10 annual cycles have steadily increased from 20.8 to 23.0 °C since 1970. The recurrence of temperature> 23.0 °C for 1961–1970 was 2 cases and has increased 2.5 times in recent years. This increases the likelihood of sleepless periods. The positive trend leads to a shift in the dates of the steady transition of the average daily air temperature through 5 °C and the duration of the growing season. Over the last 18 years (2001–2018), it increased by 11–16 days (225 and 209–214). The incidence of such cases increased from 22 % to 44–50 %. At the same time, the increase in the duration of the period with an average daily temperature of ≥10 °C is not statistically significant. The average sums of effective temperatures ≥5 °C over the 10-year cycles in 2011–2018 were 2711 °C, which is 347 °C higher than the base period (1961–1990). Temperature totals increase linearly from 1971 to 2018. However, their recurrence (≥2711) in 2011–2018 sharply increases to 50 %. A close correlation (R2 = 0.75) was established between the duration of the period at ≥5 °C and the sum of effective heat ≥5 °C. A similar trend is typical for effective temperatures at ≥10 °C. The results of the accounting of crops show that for the whole period of observations their average values were: winter wheat (steam) – 4.44 t/ha; spring barley – 2.40 t/ha; corn – 4.32 t/ha; sunflower – 2.15 t/ha. Their distribution was characterized by significant fluctuations due to the variability of weather conditions. However, its maximum levels were noted in the post base period. Against the background of increasing supply of thermal resources in the region, there is an increase in their average yield: steam of winter – by 36 % (3.76 and 5.12 t/ha); spring barley – 24 % (2.14 and 2.65 t/ha ), corn – 11 % (4.14 and 4.59 t/ha), sunflower – 30 % (1.86 and 2.42 t/ha). The probability of forming the optimal yield level of steam winter, spring barley, corn and sunflower (≥4,44; ≥2,40; ≥4,32; ≥2,15 t/ha, respectively, for crops) in the post base period reaches 56–76 % whereas in 1961–1990 it was 25–43 %. Keywords: thermal resources, sum of temperatures, field crops, yield dynamics, adaptive properties.