In the research study, the effect was determined of the genotype, phosphorus and potassium fertilization, of foliar application of nitrogen, and of Moddus and Promalin plants growth regulators on the transmission of photosynthetic active radiation (PAR) by the oat canopy. Owing to a strong impact of phosphorus and potassium fertilization on the PAR transmission, its effect was also determined on the content level of nitrogen in green matter of oats; the determination was made on six diverse days of the entire research project performed (i.e. on the 26^th, 41^st, 48^th , 56^th, 61^st , and 70^th day after the sowing day). The experiment was conducted according to a fraction plan 2^5-1 in Wierzbica (50°29’ N; 19°45’ E ) at 290 m AMSL. The research results confirmed the statistically important effect of phosphorus and potassium fertilization on the PAR quantity transmitted by the oat canopy on four (4) investigation days in June. The effect studied, expressed in standard deviation units, varied from 0.254 to 0.347. In addition, it was confirmed that the PAR transmission by a STH 7000 dwarf genotype was statistically significantly higher if compared to the transmission by the Akt cultivar. The foliar application of nitrogen caused the content of nitrogen in the green matter of oats to essentially exceed the values as indicated by the nutritional standards ref. to ruminants, but, it did not cause the values of optimal nutrition of oat plants to be exceeded on the six days of investigation.