Response of new forms of winter oilseed rape with modified fatty acid composition to nitrogen and sulfur fertilization

In a field experiment conducted at the Lagiewniki Farm (west Poland) in the years 2015-2018, the reaction to fertilization with nitrogen (100, 160 and 220 kg N/ha) and sulfur (0, 30, 60 and 90 kg S/ha) of three forms of winter oilseed rape (WOR) (Brassica napus L.) with different quality of oil characteristics was studied. The Monolit variety with typical fatty acid composition for the double-improved cultivars, was compared with two forms with changed fatty acid composition obtained using chemically induced mutagenesis: the variety Polka-type with high oleic acid content (C-18:1, 78%) and the line PN440-type with increased oleic acid content (C-18:1, 75%) and reduced linolenic acid content (C-18:3, 3%). The studied WOR genotypes reacted similarly to fertilization factors. A significant increase in seed yield (8%-14%, 0.26-0.4 t/ha) was visible up to the maximum nitrogen (N) dose (220 kg/ha). Sulfur fertilization increased seed yield by 4%-7% (0.15-0.22 t/ha). A significant interaction between N and S has been demonstrated. The highest seed yield at moderate N fertilization (160 kg/ha) was ensured by a 30 kg/ha S dose, while at a high N dose (220 kg/ha) the highest yield was observed at application of 60 kg S/ha. Regardless of the N dose, the highest net and marginal effectiveness of 1 kg S (about 6 kg of seeds) for all investigated forms of oilseed rape was observed at the lowest S dose (30 kg S/ha). Sulfur fertilization increased (by 3.5%-5.5%) the efficiency of the N used.