Document Type : Research Article
Authors
1 Graduate of the Department of Soil Science and Engineering, College of Agriculture and Natural Resources, University of Tehran; Karaj, Iran
2 Associate Professor, Department of Soil Science and Engineering, College of Agriculture and Natural Resources, University of Tehran; Karaj, Iran
3 Assistant Professor, Ilam Agricultural Research Center, Agricultural Research, Education and Extension Organization, Ilam, Iran
Abstract
Introduction
The cultivation area of canola (Brassica napus L.) has increased globally due to its climatic adaptability and its different growing season compared to other oilseeds. Additionally, its ability to be cropped in rotation with other plants, such as cereals, has contributed to its popularity. Canola has the largest cultivated area among oilseed crops in Iran. Proper consumption of nutrients is crucial for improving growth and increasing seed yield in canola plants. The use of sulfur as an essential nutrient, along with selenium in low concentrations as a beneficial nutrient, plays a significant role in enhancing plant tolerance to environmental stresses. Sulfur and selenium are both elements of group 16 of the periodic elements table and have similar physical and chemical properties, and it is believed that selenium utilizes the same pathways for sulfur immobilization and uptake in plants. Given the similarity of selenium to sulfur, sulfur metabolic pathways are shared, so the effect of selenium on growth is expected to be largely influenced by sulfur nutrition. This study aims to investigate the effects of sulfur and selenium application on nutrient absorption and their interaction on canola plant growth indices.
Materials and Methods
The experiment was conducted in greenhouse conditions as a factorial in a completely randomized design with 12 treatments and three replications. For cultivation, plastic pots with a diameter of 20 cm were utilized. Four kilograms of sieved soil were added to each pot. 100 mg kg-1 of nitrogen from urea source was applied in the pre-planting stage and 100 mg of nitrogen was applied in two stages (after establishment on day 21 and then in the stem elongation before flowering stage). Triple superphosphate at a rate of 80 mg of phosphorus per kg of soil was added to the pots in powder form before planting and iron at a rate of 5 mg kg-1 in the form of iron chelate solution was added to the pots. The experimental treatments included elemental sulfur fertilizer at two levels of zero and 20 mg kg-1 (inoculated with Thiobacillus inoculum), two sources of selenium fertilizer (sodium selenate and selenite) at three levels of zero, 30, and 60 μg/kg in soil form before planting. The amount of sulfur and selenium available in the soil before planting was 3.8 and 0.025 mg/kg, respectively. The cultivated canola variety was Dalgan and grown in greenhouse conditions for 5 months. This cultivar is open-pollinated. The sulfur was in powder form with a purity of 99%, which was added to the soil of the sulfur-containing treatments, along with Thiobacillus inoculum (with a population of 1×108 cells per ml) two weeks before planting. After the seed growth and maturation period (5 months), at the final stage of growth (physiological maturity with a two-digit growth code of 80), the seed components were separated from the aerial parts. The dry weight of the seed and the aerial parts of the plant were weighed separately.
Results and Discussion
Sulfur application significantly increased shoot dry weight, root dry weight, leaf area, and canola grain weight compared to conditions without sulfur application (48.8% increase in shoot weight, 28.1% in root weight, 15.7% in leaf area, and 51.3% increase in grain weight). Grain weight had a correlation of 0.94** with grain sulfur uptake and 0.9** with shoot sulfur uptake. Therefore, the growth characteristics of roots, shoots, and sulfur concentration in shoots and seeds have a significant impact on grain weight. Application of selenium from selenate source resulted in higher selenium absorption in shoots and canola grain compared to selenite source. In grain, sulfur application increased selenium absorption from both sources. Grain sulfur uptake had a correlation of -0.42** with seed selenium concentration, 0.94** with seed weight, 0.86** with shoot sulfur concentration, -0.43* with shoot selenium concentration, 0.87** with shoot sulfur uptake, 0.7** with shoot weight, 0.69** with leaf area, and 0.83** with root weight. The highest grain selenium concentration was observed at the rate of 60 μg kg-1 from selenate source (0.48 mg kg-1). If increasing the selenium concentration of the grain is desired for enrichment purposes (from 0.12 μg g-1 in the sulfur-free and selenium-free treatments), a sulfur treatment of 20 mg kg-1 and a selenate content of 60 μg kg-1 could be considered to achieve a concentration of 0.42 μg g-1. This is because the grain weight of this treatment (3.87 g pot-1) was closest to the high levels of grain weight in the sulfur treatment of 20 mg kg-1 and selenium-free condition (4.32 g pot-1).
Conclusion
Grain selenium concentrations of 0.10-0.11 mg kg-1 and sulfur concentrations of 0.325-0.33% produced suitable canola yield. The highest canola grain weight was obtained with a concentration of 19.86 mg kg-1 sulfur and 0.0267 mg kg-1 selenium in the soil.
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