The effect of placement and light conditions during foliar application of Insol U fertilizer on gas exchange, yield and the quality of spinach (Spinacia oleracea L.)

Pot experiments conducted in a growth chamber studied the effectiveness of foliar fertilization of spinach (Spinacia oleracea L.) with macro- and microelements in the form of a 1% water solution of Insol U fertilizer applied with fluorescent light of the PAR intensity of 200 μmol m^-2 s^-1 and with dispersed daylight of the intensity of 600 μmol m^-2 s^-1. Insol U was applied three times, supplied on the upper, lower or both sides of the leaf blades. The control consisted of plants sprayed with distilled water. The obtained results pointed out that foliar fertilization of spinach with Insol U significantly increased the leaf gas exchange, the yield of the fresh leaf mass, the content of vitamin C, chlorophyll, carotenoids, as well as potassium and phosphorus in the leaves. The application of the fertilizer onto the upper and the lower side of the leaf blade had the most positive effect on the analysed property of the leaves. Independently of the side leaf, the application of the fertilizer at a higher light intensity had a significantly better consecutive effect on all the analysed properties of the leaves.