Abstract
<jats:p>The article presents the results of a two-year field study (2023-2024) aimed at identifying the key factors that determine the yield of buckwheat varieties Dikul and Dasha under the conditions of the use of traditional urea and urea treated with the B.s. Ch-13 crop. It has been established that the productivity of the crop depends only 50% on the degree of development of the photosynthetic apparatus, estimated through the ratio Σ ChL/carote (the sum of chlorophylls a and b to carotenoids). The aim of the study was to assess the effect of urea inoculated with the Bacillus subtilis Ch-13 strain on the activation of the photosynthetic apparatus in buckwheat plants of different breeding years, as well as to identify the dependence of stimulation efficiency on the physiological characteristics of varieties due to their breeding history. For the Dikul variety, exceeding the dose (N90) leads to a decrease in grain yield (2023: 13.7 c/ha; 2024: 12.5 c/ha) and an increase in straw (2023: 61.0 c/ha; 2024: 59.3 c/ha), which is associated with an imbalance of Σ ChL/Karot (>13) and the redistribution of assimilates into the vegetative mass. For the Dasha variety, modified nitrogen (N60m) increases yields by 8–10% compared to conventional N60, probably due to improved photosynthetic activity (Σ ChL/Karot ~10–11).</jats:p>