The article presents the results of laboratory and field experiments on studying the influence of ways of presowing seed treatment and methods of reducing the amount of coumarin on yield and forage quality of sweet clover in the conditions of Northern Kazakhstan. The aim of the research is to study and to prove the effective way of presowing treatment of seeds and a method of decreasing the content of coumarin in order to increase the productivity and to improve the quality of clover forage. The experimental station of the North-Kazakhstan SRI of agriculture in 2015-2016 was conducted pursuant to the solution of tasks. In our experiments, it was shown that the proposed method of presowing treatment of sweet clover seeds improves the laboratory germination from 65.2 to 99.0% and the field germination from 33.1 to 72.8%. When applying the technique of reducing the content of coumarin, its content in the green mass of clover was 1.14%, in the hay dried at a temperature of 20°C-0.65% and at a temperature of 60°C-0.48%. The coumarin content decreased two times. The protein content of the hay dried at a temperature of 20°C was 13.2%, at a temperature of 60°C-15.1%. The content of fodder units at a temperature of 20°C was 0.39%, at a temperature of 60°C-0.47%. Based on the research results on studying ways, which increase seed germination and methods of reducing the amount of coumarin in sweet clover, the way of presowing treatment of sweet clover seeds, which increases seed germination almost by 100% and an effective technique of making sweet clover hay, which reduces the coumarin content to safe limits for animals, as well as increases the fodder value of sweet clover hay, were developed and proposed for the production. The method of increasing seed germination of sweet clover is simple in the technical performance and not costly from an economic point of view, which is performed by soaking the seeds of sweet clover in water for 24 h, with further drying and separating the swollen soft seeds on a sieve with a diameter of 2.5-3 mm and the process ends by scarification. The essence of the method of reducing the coumarin amount is that sweet clover, in connection with the content of antinutrient-coumarinin the vegetative mass, should not be fed in the green form and hay making should be fulfilled by the method of active aeration at a temperature of 60°C. Along with the decrease in the content of coumarin, the quality indicators of hay increase. Hay, dried by active aeration at a temperature of 60°C, is bright-green, well-foliated and has a pleasant smell.

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The paper presents the evaluation of the total combining ability of the seed parents of white sweet clover Melilotus albus and yellow sweet clover Melilotus officinalis based on leaf formation, forage productivity and seed productivity. The results of competitive heterosis for the yield of herbage, dry matter and seeds of the polycross offspring Syn1 are also presented. Among the polycross offspring Syn1 Melilotus albus, SGP-4-12507 and SGP-5-12508 were selected based on their leaf formation (50 and 50%, respectively); competitive heterosis was 16.3 and 22%, respectively. Based on the total combining ability of offspring Syn1 of Melilotus albus, the following biotypes were selected: SGP-2-12519 (27.1%) and SGP-1-12503 (20.8%) for forage productivity; SGP-4-12601 (14.7%) and SGP-5-12508 (13.0%) for dry matter productivity; SGP-4-12601 (50.4%), SGP-2-12519 (19.2%) and SGP-5-12508 (14.1%) for seed productivity. The highest total combining ability were found for the following biotypes of Melilotus officinalis: SGP-9-12454 and SGP-10-12455 for leaf formation (18.2 and 13.3%, respectively); SGP-10-12455 (12.5%) for herbage productivity; SGP-10-12455 (29.6%) and SGP-9-12454 (24.2%) for dry matter productivity; SGP-6-12520 (15.4%) and SGP-9-12454 (14.1%) for seed productivity. Selected sweet clover samples can be recommended as the best basic material for further work on selection for high forage and seed productivity.