INFLUENCE OF SOIL AND POST-EMERGENCE HERBICIDES ON THE CONTENT OF PLASTID PIGMENTS AND PRODUCTIVITY OF SOYBEAN PHOTOSYNTHETIC POTENTIAL

Abstract

The purpose of the research was to find out the nature of the effect of herbicide mixtures on soybean
photosynthetic mechanism and the productivity of sowing. The experiment options included: control without
weeding; control with two hand weeding; Primexstra TZ Gold (S-metolachlor, 312.5 g/l + terbuthylazine,
187.5 g/l), 4.5 l/ha; Zencor (metribuzin, 700 g/l) + Command (clomazone, 480 g/l), 0.4 l/ha+0.2 l/ha;
Bazagran (bentazone, 480 g/l) + Harmony (thifensulfuron-methyl, 750 g/kg), 2.5 l/ha+0.008 kg/ha. The
effectiveness of the preparations was researched in the field experiment at the separated subdivision of
NUBiP of Ukraine “Agronomic Research Station” using the traditional technology for the Forest-Steppe
zone of Ukraine. Soil herbicides were applied before seedlings’ emergence, and after it – when the first true
leaf appeared. The pigment content was determined spectrophotometrically after extraction with DMSO
(dimethyl sulfoxide) according to the method of A. Wellburn (1994). Statistical processing of received values
was performed by using Excel 2016 software package. It was found that under the action of herbicides, the
content of total chlorophyll in soybean leaves was by 15–20 % higher than in the control without weeding. At
the same time, the phytotoxic effect of herbicides led to a decrease in the content of chlorophylls in
comparison with the non-herbicidal control at double hand weeding. Furthermore, a simultaneous increase
in the content of carotenoids was fixed, and it was obviously a reaction of the plants to the induced oxidative
stress, resulting in inhibiting pigments’ biosynthesis. However, stress factors ensured a significant activation
of photosynthetic processes, which was confirmed by the increase in a ratio of basic photosynthetic
pigments. Using tank mixtures of herbicides, the ratio of a, b chlorophylls was twice as much as in both
controls. The activation of the plants’ photosynthetic apparatus under the action of herbicides led to the
accumulation of optimal photosynthetic potential (PP) of sown areas and ensured their higher productive
capabilities. In the variant where tank mixtures of Zencor + Command and Bazagran + Harmony were used,
the productivity of the PP (PPP) made 1.16 and 1.45 kg of yield per 1,000 of PP units, which was higher
than the control without weeding by 28 % and 42 %, respectively. Thus, the applying of tank mixtures of
selective soil and post-emergence herbicides favored the activation of photosynthetic processes in soybean
plants and ensured productivity indices at the level of non-herbicidal background with hand weeding.