Title : The use of attractants and biofortification with nutrients in seed production of white clover (Trifolium repens L.)
White clover (Trifolium repens L.) is one of the most important, perennial, multi-seeded legumes grown in Poland. The cultivation of white clover ranks third in terms of economic importance among fineseeded legumes in Poland. T. repens is distinguished by high digestibility of the organic matter and high protein content. The Polish register of varieties includes eight varieties of white clover, recommended for pasture cultivation with grasses, permanent mountain pastures or dry soil. T. repens is a natural allotetraploid, allogenic species and is characterized by an entomophily, xenogamic pollination pattern.
One of the reasons for the low yield of seeds of this species is the insufficient supply of pollinating insects in the areas where they occur. The main pollinators of T. repens are representatives of the Hymenoptera order of the true bee family (Apidae), the honeybee Apis mellifera L. and various species of bumblebees (Bombus). In Polish conditions, however, the role of bumblebees in pollination of white clover does not exceed 12-15%. Honeybees make as much as 85-88% of pollination of white clover. In order to improve pollination of clover flowers and seed setting, bee attractants and biofortification with microelements can be used. The attractants are based on substances that occur naturally in nature - aromatic compounds and pheromones, which stimulate insects to work, and its active ingredients imitate the pheromone secreted by scout bees to indicate the source of the honey flow to collectors. Hence, the aim of the research was to develop an innovative technique of seed production of white clover. The research was conducted in the central-eastern part of Poland (φ = 51°34´, λ = 23°02´, H = 157 m above sea level), in the years 2015-2017. The experiment was established using the randomized sub-block method, in a dependent, split-plot design, in four replications. The first order factor was the application of the attractant - Pollinus, in two terms and the control object, without the use of the attractant. The second-order factor was biofortification of clover with fertilizers. The object of the research was the Polish variety of diploid white clover. The meteorological conditions of the growing season had a decisive influence on the seed yield and the main elements of its structure. The highest seed yield was obtained in 2016, characterized by more favourable thermal conditions and rainfall in the clover generative subperiod, and the lowest in the extremely dry subperiod, 2015. The attractant application significantly increased the number of heads, the share of seeds in the head, the weight of a thousand seeds and their yield, as well as seed germination. Biofortification with microelements (B+Mo) significantly increased the number of inflorescences per 1 m2, the number of seeds in the head and their yield per unit area, compared to standard PK fertilization. The best results of the attractant application were obtained when the preparation was applied twice, in stages 60 and 65, on the 99° BBCH scale, compared to the control object. The highest yield of T. repens seeds was obtained thanks to biofortification with boron and molybdenum and the use of the Pollinus attractant in relation to fully flowering plants.