Photosynthetic parameters of winter pea sowings under the effect of nitrogen fertilization and seed inoculation in the Right Bank Forest-Steppe of Ukraine

Purpose. To evaluate the photosynthetic parameters of winter pea sowings under the effect of seed inoculation and nitrogen fertilization in the Right Bank Forest-Steppe of Ukraine.
Methods. The research was carried out in the years 2019–2021 in the fields of the Agronomic Research Station (a division of NULES of Ukraine, Kyiv region). Winter pea ‘NS Moroz’ was sown in the second half of September at the rate of 1.2 million seeds/ha. The width of the rows was 15 cm, and the seed sowing depth was 4–4.5 cm. The design of the experiment provided for the combined use of such technological factors as seed inoculation (without inoculation; Optimize Pulse, 3.3 l/t) and nitrogen fertilizer [main application + early spring top dressing (N0; N15 + N15; N15 + N30; N15 + N45; N30 + N0; N30 + N15; N30 + N30; N45 + N0; N45 + N15; N60 + N0)]. P45K45 was also applied in the primary fertilization as a background.
Results. Seed inoculation and nitrogen fertilizers positively affect the photosynthetic activity of winter pea; however, the efficiency of their action largely depends on the application doses and timing, as well as the stage of crop development. It was established that in the autumn period of winter pea vegetation (complete sprouting–stalking), the influence of the studied agrotechnical measures on the leaf area index (LAI), photosynthetic potential (PP), and net photosynthetic productivity (NPP) was mostly insignificant. In the period of spring-summer vegetation, the effect of the factor of seed inoculation, as well as early spring fertilization with nitrogen, increased significantly, while the main fertilization decreased. The highest LAI (on average according to the experiment 31.4 thousand m2/ha) was formed in the flowering stage, PP during the stages of bean formation – ripening of seeds (0.75 million m²/ha per day). The use of seed inoculation compared to options without it contributed to the increase of these indicators by 5.33 and 0.17 million m2/ha per day, respectively. In the experiment, the maximum values of both LAI (35.77–36.45 thousand m²/ha) and PP (0.91–0.93 million m2/ha per day) were obtained when applying N15 + N30–45 and N30 + N30 on the background of seed inoculation, while the minimal in control treatments (N0). The regularities of the formation of the NPP were radically different. Its highest indicators during the period of the beginning of vegetation – budding (as well as in the following interphase stages) were observed primarily with the minimal application of fertilizers (N30 + N0, N15 + N15) or in the control treatments (N0), 8.1–9.2 g/m2 per day. Seed inoculation had no significant effect on the formation of NPP. The maximum content of chlorophyll a in plants (5.90 mg/g) was formed in the budding stage, gradually decreasing to 5.74 and 5.05 mg/g in the flowering and bean formation stages, respectively. Instead, the content of chlorophyll b was the lowest in the budding stage (12.37 mg/g), reaching its maximum in the flowering stage (19.71 mg/g) and slightly decreasing in the stage of bean formation – 16.37 mg/g of raw mass. Seed inoculation helped to increase the content of chlorophyll a by an average of 0.9–1.0 mg/g over growth stages and chlorophyll b by 1.4–2.2 mg/g. The best fertilization treatment was N15 + N30–45.
Conclusions. Seed inoculation and nitrogen fertilization are significant and effective factors to intensify the photosynthetic activity of winter pea sowings. The patterns of the parameters of leaf s area, photosynthetic potential, net productivity of photosynthesis, and the content of photosynthetic pigments revealed in the study may be used to improve the cultivation technology to fully realize the crop potential productivity under the conditions of the Right Bank Forest‑Steppe of Ukraine.