| Summary: | The aim of the research is to study the features, qualitative and quantitative patterns of soil water regime formation during sprinkling irrigation, collectively allowing characterize the conditions of water supply of soybeans from the standpoint of technological process optimization. The object of the research is irrigated soybean agrophytocenoses. The subject of the research is the soil water regime in irrigated soybeans seeds. The study materials were the results of their own field experiments implemented in 2010–2017 on the irrigated lands of Agrofirm Vostok JSC, Nikolaevsky district of Volgograd region (Volgograd Zavolzhie). The experiments included options with soybean varieties, fertilizers, and irrigation regimes, but the data sample for this study was formed according to the characteristics of the problem to be solved. The experiments confirmed that the irrigation frequency of soybeans is an extremely dynamic, unstable parameter, determined mainly by meteorological conditions. Relatively stable trends with the determination coefficient 0.40–0.69 were established only in terms of reducing the irrigation frequency with an increase of antecedent soil water threshold. For the studied varieties the data indicating a reduction of the irrigation interval in later-ripening soybeans were obtained. As a rule the observed differences estimated at 2–4 days are well correlated with a more developed vegetative mass of soybean varieties of late ripening. The qualitative differences in the dynamics of soil moisture between irrigations are established. The dynamics of soil moisture decrease between irrigation during the period “seeding – early flowering” is characterized by a curvilinear trend, the form of dependence during the period “seeding – the beginning of branching” and the period “branching – early flowering” varying significantly. Since the beginning of the soybean flowering phase, soil moisture between irrigation decreases along a linear trend. Registration of these differences allows us to assess the weighted average soil moisture more accurately and hence the water supply conditions for soybeans according to the growth and development phases.
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