Application of biological preparation under conditions of introduction of farming system with biological approach is one of the prospective ways of improving the productivity of agricultural crops, including lentil. However, the influence of plant growth regulators and microbiological preparations in lentil crops needs further research, which determined the aim and tasks of our research. The article presents the results of the field experiment on the influence of microbial preparation (Rhizobium leguminosarum biovar viceae strain K-29 (1.0l/t of seeds)) and plant growth regulator Regoplant (250 ml/t – pre-sowing treatment of seeds; 50ml/ha –post-germination application) on the formation of leaf area and net productivity of the photosynthesis of lentil variety Linza. The leaf area was calculated according to the methods, described by Z.M. Hrytsayenko et el., net productivity of crops photosynthesis was determined according to the method by O.O. Nechyporovych. Statistical data processing was performed, using the method of dispersion analysis by B.A. Dospiekhov. The results of the research have shown that photosynthesis productivity of lentil crops depends on the weather conditions, application of biological preparations, growth stage and development of crop. It has been noted that the integrated application of plant growth regulator and microbial preparation has a positive influence on the formation of leaf area apparatus and net productivity of photosynthesis of lentil crops. On average, the optimal leaf apparatus area of lentil variety Linza was formed at the flowering stage under pre-sowing treatment of seeds with the composition of microbial preparation Rhizobium leguminosarum biovar viceae strain K-29, 100ml/ha of seed rate and plant growth regulator Regoplant, 250ml/t with its further post-germination application at the rate of 50ml/ha, which exceeded the index by 25%. The same variant provided the increase in the net productivity of photosynthesis by 16%

Keywords: lentil, microbial preparation, plant growth regulator, the area of leaf apparatus, net productivity of photosynthesis