The Response of Growth and Yield of Canola Genotypes to Humic Acid Application in Different Plant Densities

To determine the effect of plant density and humic acid on canola yield, a 2-year field experiment was conducted as a factorial split-plot during the 2014-2016 cropping years. The factors included two humic acid levels (humic acid solution at 3/1000 [v/v] concentration and distilled water) and three plant densities (40, 60, and 80 plants per m(2)) in the main plots and six canola genotypes (Ahmadi, Okapi, Opera, Nafis, Karaj1, and SW102) in the subplot. The results showed a significant decrease in the grain and oil yield when plant density increased from 40 to 80 plants per m(2), by 57 and 59%, respectively. The oil quality was also effected by the plant density, so the erusic acid and glucosinolate contents increased twofold at 80 plants m(2). The grain and oil yield were significantly higher in plants treated with humic acid compared to controls, by 5.4 and 5.8%, respectively. Moreover, the foliar application of humic acid enhanced the oil quality of canola genotypes through a significant decrease in erusic acid and glucosinolate contents. However, there was no significant decreasing effect of humic acid on the density-induced yield loss and the oil yield reduction. Therefore, the increase in canola yield might be achieved by selecting the optimum density and improving the nutritional condition of the soil.