Soybean productivity depending on available soil water in the Right-bank Forest-steppe zone of Ukraine

Abstract

The availability of  moisture in soil during soybean grow can vary depending on many environmental factors, as well as growing technologies. The purpose of our research was to determine the influence of the width of the row and the density of plant standing on the reserves of available moisture and total water consumption in the cultivation of various soybean varieties. The need for soy in water depends on the growing season, varieties of soy, irrigation, rainfall and other factors. During vegetation period, plants of soybeans, in Ukraine, in hot summer months (July-August) requires more water than cultivating soybean plants under more favorable conditions (May-June). Soybean growth require for the availability of sufficient amounts of available moisture. Favorable weather conditions play an important role in obtaining high yields. However, according to the UkrHydrometcenter in Ukraine, extreme weather conditions are increasingly observed in recent years. Thus, during June 2017, the strongest drought in the past 10 years was recorded. The coefficient of water consumption of a plant may be changed by various agronomic measures, in particular, reducing the process of evaporation of moisture from the surface of the field by mulching, changing the density of plants, selecting a variety with a rapid initial development during the first stages of vegetation period, and with  root system that is able to penetrate into the deeper soil horizons, by different seeding dates and fertilizers. Preserving the existing moisture in the soil, additional irrigation, soil cultivation to improve infiltration and reduce surface drainage, control of weeds can control the water consumption of cultivated plants and increase yields. The reserves of available moisture on the soil layers may vary, and may vary depending on the width of row spacings, the density of plant standing and many other factors. Therefore, today it is
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relevant to study the influence of geometric placement of plants and soil moisture on the productivity of soybean plants. Drought affects the various physiological and morphological characteristics of soybean plants, which, in turn, affect the formation of tuber bacteria, fixation of nitrogen, growth of a plants and level of the yield. The stress of plants that was caused by drought may depend on a variety of factors, such as the BBCH phase, the severity and duration of stress for soybean plants. Soil moisture deficiency can affect plants in different ways, ranging from visual changes to the wilting and death of the entire plant, due to the dying tissue. The purpose of the research was to determine the dependence beetween the level of soybean yield and factors such as varieties (Alligator, Senator and Mentor), row spacing (12.5 cm, 25 cm, 45 cm) and seeding density per hectare (500, 600, 700 thousand similar seed / ha). The total area of the experimental plot is 300 squared meters, the accounting area is 250 squared meters. Placement of territories - randomed, repetition - four times. The analysis of weather conditions in 2016 showed the variability of weather conditions during the growing season. Regarding precipitation, the April and July months were significantly dry, and May was extremely wet, and June and September tended to dry. Thus, the development of the soya plants in 2016 had a significant dependency with weather conditions during the critical periods of its growth. In 2017, it had typical weather conditions with a tendency to decrease rainfall in most months. The results of the study showed that there is a positive correlation coefficient of 0.53 between the yield and the total water consumption in the layer of soil 0-100 cm. This means that in cases with higher yield, we observe more intensive water consumption. The average experimental value of the total water consumption was 137.8 mm, and the water consumption coefficient was 39.16 mm per tonne of yield, which means that for the formation of one ton of crop, soy plants spent 39.16 mm of soil moisture. The largest indicator of the total water consumption of 163.08 mm was recorded in the Mentor variety with density of 600 thousand plants per hectare and with width of the row equal to 12.5 cm. According to the results of the study, a correlation coefficient of 0.73 was found between the total water consumption (in the layer of soil 0-100 cm) and the density of
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plants, which means that with increased density, we observe an increase in the consumption of available moisture by soybean plants. A correlation coefficient of 0.53 was established between the yield and total water consumption, indicating a good correlation between these indices. The density of standing and the width of the row can have influence in various ways on the reserves of available moisture in the soil. The results of the study showed a close correlation between plant density and total water consumption, and between crop yield and total water consumption, the average, which means that more intensive water consumption was observed at higher densities and, consequently, for higher yields, respectively.