Effects of Biostimulants on Cold Stress in Late Sowing of Rape (Brassica napus ssp. oleifera L.) under Arak Province Conditions in Iran

Abstract

Cold stress limits the yield of rapeseed (Brassica napus spp. oleifera L., Okapi) in late sowing. The experimental design was a split plot with three replications in two years (2018-2019). The main plot had two sowing dates (the first sowing on 18 September and the second one on 10 October). Biostimulants treatment included: Blank (fertilizers according to the soil test without biostimulants); Blank with humic acid fertigation; Blank with fulvic acid; Blank with amino acid; Blank with seaweed extract; Mixed treatment consisted of humic acid, fulvic acid, seaweed, and amino acid. Humic acid was used at the second irrigation and six-leaf stage (5 kg ha^-1). Fulvic acid, amino acid, and seaweed extract were used as foliar at the six-leaf stage and stem elongation (0.5% and 0.3% w/v in mix treatment). Based on the results, the main effect of biostimulants on grain yield, nitrogen (N), and phosphorus (P) uptake was significant. The difference between the two sowing dates on shoot dry weight (DW) and grain yield (3458 vs. 3048 kg ha^-1) was significant. The seaweed improved the grain yield in delayed cultivation by 34% compared to the control and had the highest profit-to-cost ratio in normal cultivation (15.1) and in delayed cultivation (13.7).