FORMATION AND PHOTOSYNTHETIC ACTIVITY OF MIXED AGROPHYTOCENOSES WITH SWEET CLOVER (MELILOTUS)

The article presents the results of studying the characteristics of the formation of annual forage crops in mixed agrophytocenoses, their photosynthetic activity depending on the mixture components, seeding rates in the mixture, the background of mineral nutrition. The studies were conducted in the three-factor field experiment in 2015-2017 on the experimental field of the Penza Agricultural Institute – a branch of the FSBSI Federal Scientific Center for Bast Crops. The studies were carried out according to generally accepted methods on leached medium loamy black soil, with a high and elevated content of available forms of macronutrients. Annual forage crops (Sudan grass (Sorghium vulgare), maize, sawa millet (Echonichloa frumentacea), foxtail millet (Setaria italica), amaranth (Amaranthus)) were studied in mixed sowing with a white sweet clover (Melilotus albus). The seeding rates of the legume and associated components were 70 + 40%, 55 + 55%, 40 + 70% of the total norm. As a nutritional background, the doses of mineral fertilizers N45P45K45 (background 1) and N60P60K60 (background 2) were studied. The purpose of the research was to study the formation and photosynthetic activity of agrophytocenoses of annual forage crops in mixed sowings with white sweet clover in the forest steppe of the Middle Volga region. It was established that the germination and preservation of annual grasses in mixed sowings depended on meteorological conditions during the years of research, a concomitant component in the mixture, seeding rates of components and mineral fertilizers. The most developed photosynthetic potential (regardless of other factors) was in mixtures of sweet clover with amaranth – 2.65 million m2 day/ha and of sweet clover with sawa millet – 2.08 million m2 day/ha. The seeding rate of 40 + 70% and the increased background of nutrition (N60P60K60) contributed to obtaining high rates of photosynthetic potential – 2.01 and 2.23 million m2/ha, respectively. The highest indicators of the net productivity of photosynthesis were obtained in mixtures of sweet clover with Sudan grass and of sweet clover with maize – 7.95 and 7.70 g/m2 per day, with a seeding rate of 40 + 70% – 6.55 g/m2 per day and on natural fertility (control) – 6.64 g/m2 per day.