The absorption and utilization of photosynthetically active radiation (PAR) by soybean sowing greatly depends on the variety, nutrition background and sowing rate that gives the possibility to adjust their sizes. Absorption of PAR is closely dependent on the density of sowing and of a leaf area – r = 0,86-0,94. The maximum absorption of PAR by soybean crops is 82-83% and is reached at a leaf area 44-50 thousand m2/ha, and increasing it does not increase the absorption coefficient. A significant part of PAR is reflected from the plantings (11,0-14,8%), takes place to the soil (4,2-24,8%) and is not used by plants. The best conditions for the absorption of solar energy by the crops soybean varieties Aratta and Sofia were at the seeding rate of 600 thousand/ha and of seed inoculation.
2,50-3,72% from PAR that comes on sowing was used on forming of soybean yield. More effectively solar energy was used by sowings of the varieties Sofia – 2,91-3,72%, an the varieties Aratta – 2,50-2,92%. Inoculation and mineral fertilizers in the dose of N30P40 increased the absorption of solar energy of both varieties. The higher dose of nitrogen fertilizer is not effective. Soybean most efficiently uses solar energy on sowing with the seeding rate of 600 thousand seeds per 1 ha and at the nutrition background N30P40 + inoculation of seed. Between the size of the coefficient of use of PAR and soybean yields there is a close positive relationship – r = 0,965. To obtain high soybean yields it is important to establish such plantings which would absorb and use solar energy maximum.
Key words: soybean, solar energy, variety, sowing rates, nutrition background.