Water and Soil

Abstract Introduction: Soil salinity in arid and semi-arid regions is one of the important factors that limits crop production, and affects plant yield through various mechanisms. Chlorophyll destruction and reduction of leaf area due to high sodium concentration leads to a decrease in photosynthesis. The application of humic acid and amino acid with hormonal effects and adjustment of nutrients has been suggested to reduce salinity stress. The experiment aimed to investigate the effect of plant growth biostimulants and salinity levels on the growth indices of two canola cultivars in greenhouse condition.
Materials and Methods: This study was carried out as a factorial study based on a completely randomized design with three replications. The three experimental factors included: 1) salinity factor in three levels (0.571, 4, and 8 dS m-1), 2) canola cultivars in two levels (Hyola 50 and Dalgan), and 3) types of plant growth biostimulants in four levels (amino acid, humic acid, a combination of these two biostimulants, and a control treatment with no biostimulants application). Before the flowering stage (8 weeks after planting), the plants were harvested and some morphological traits including plant dry weight, root dry weight, and the concentration of calcium, sodium, and potassium in the shoot were measured.
Results and Discussion:
Based on the results, the cultivar Hyola 50 (8.35 g plant-1) had a significantly higher shoot dry weight than the cultivar Dalgan (7.58 g plant-1). The reduction in shoot dry weight at a salinity level of 8 dS m-1 was 19.3% compared to the treatment of 0.571 dS m-1. At salinity levels of 0.571 and 4 dS m-1, there was no difference between the effects of biostimulant treatments compared to the control (without biostimulants). But at a salinity level of 8 dS m-1, the shoot dry weight of the humic acid treatment (7.26 g plant-1) was significantly higher than the control treatment (16.6 g plant-1) (17.9% difference). The effect of humic acid application on leaf area (748 cm2 plant-1) was greater than that of amino acid foliar application (670 cm2 plant-1). With an increase in salinity level to 8 dS m-1, the dry weight of roots decreased. The highest dry weight of the root in the Dalgan cultivar at 8 dS m-1 was obtained in the combined treatment (0.607 g plant-1) and for the cultivar Hyola 50 in the combined treatment and amino acid (0.607 g plant-1). There was a significant difference in root dry weight between salinity of 4 dS m-1 (0.703 g plant-1) and 8 dS m-1 (0.543 g plant-1). The root dry weight of the plant was more affected by salinity stress than the shoot dry weight. In both canola cultivars, at a salinity level of 8 dS m-1, the chlorophyll index (SPAD) increased compared to a salinity level of 0.571 dS m-1 (4.6% increase in Dalgan cultivar and 9% in Hyola 50 cultivar). The shoot potassium concentration of the Dalgan cultivar (11.6%) was significantly higher than that of the Hyola 50 cultivar (92.5%), but the amount of uptake was higher in Hyola 50 cultivar (492.0 versus 459.0 g plant-1). At 8 dS m-1 salinity, the furthest potassium to sodium concentration ratio of the Dalgan cultivar was obtained with amino acid and humic acid treatment (4.87) and with the Hyola 50 cultivar with the humic acid treatment (4.21). At 8 dS m-1 salinity, the calcium to sodium concentration ratio of the Dalgan cultivar was obtained from the amino acid and humic acid treatment (12) and for the Hyola 50 cultivar from the humic acid, amino acid, and combined treatment (11). At a salinity level of 8 dS m-1, combined treatment of biostimulant in both Dalgan (1236 meq l-1) and Hyola 50 (250 meq l-1) cultivar had the highest amount of soil-soluble chlorine. This treatment may have reduced the absorption of chlorine ions by the plant. Shoot dry weight had the highest correlation with root dry weight and leaf area (0.58**). Shoot dry weight had the negative correlation with plant sodium concentration (-0.27**). The negative effect of soil-soluble sodium concentration on root dry weight (-0.39**) was greater than on shoot dry weight (-0.27**).
Conclusion: The positive effect of the application of growth biostimulants was observed through improving potassium absorption and improving the ratio of calcium and potassium to sodium concentrations in the shoot. In saline conditions (8 dS/m), the recommended phosphorus fertilizer for Dalgan variety must be 23.6%, and for the Hyola 50 variety, 10% more phosphorus fertilizer than in non-saline conditions. The application of Hyola 50 and humic acid as fertigation in saline conditions is recommended for canola.

Abstract Introduction The global cultivation area of canola (Brassica napus L.) has expanded due to its adaptability to various climates and its distinct growing season compared to other oilseed crops. 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. One hundred 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^-1 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^-1, 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.   Acknowledgements  We would like to thank the Soil Science Department of the Agricultural College of the University of Tehran for providing the facilities to conduct this experiment.