Evaluation of the Effect of Sulfur Application and Thiobacillus on Some Soil Chemical Characteristics and Yield of Canola in Wheat-Canola Rotation System

After soybean and palm oil, canola is third important oil seed in the world which belongs to the genus Brassicaceae, that its seeds contain about 40% oil. The per capita consumption of oil in Iran is about 14 kg, so approximately 900 thousand tons of oil will be required for each year. However, only less than 10% of this oil is produced in the country. In recent years, special attention has been paid to canola cultivation in order to increase oil production, so during recent years an apparent increase in canola cultivated lands is significant. In most of these canola cultivated lands, the soil is calcareous therefore; some available nutrients such as phosphorus, iron and zinc are less than the amounts required by plants. Increasing qualitative and quantitative yield of canola in calcareous soils is a priority to canola cultivation improvement. Sulfur plays an important role in oil content of oily seed crops. On the other hands sulfur oxidation in calcareous soils can improve some nutrients availability. The present study was designed to investigate the effect of sulfur on yield, oil content and nutrients uptake and also its impact on soil chemical properties with 8 treatments, in 3 replications.
This study was conducted in Ekbatan research station in Hamedan province for 2 years as completely randomized block design with 8 treatments and 3 repetitions. The treatments were: T1: Control (Without sulfur and Thiobacillus), T2: Application of 150 kg sulfur per ha, T3: T2 Thiobacillus inoculums (2% of applied sulfur), T4: Application of 300 kg sulfur per ha, T5: T4 Thiobacillus inoculums (2% of applied sulfur), T6: Application of 600 kg sulfur per ha, T7: T6 Thiobacillus inoculums (2% of applied sulfur) T8: Fertilizing based on soil test without sulfur and Thiobacillus. Thiobacillus inoculant containing about 107 cells of Thiobacillus bacteria which belonged to neutrophile Thiobacilli were prepared at soil biology Dep. of Soil and Water Research Institute. In this research treatments were applied in two separate sites (each site contains 24 plots which their dimensions were 2.4×10 meter). For evaluating the residual effect of treatments, the experiment was carried out in constant plots in second year. Phosphorus, iron, zinc, manganese and sulfate, were not applied to any of the treatments except for T8, and the above mentioned treatments were just received 250 kg urea. These all treatments were applied only in the first year and on the second year of experiment their Residual effects on canola were evaluated. During the growing season agricultural practices such as irrigation, weed and pest control in all units were managed uniformly. Soil chemical data were obtained by analyzing of Ec, pH and bicarbonate each year in May. The leaf and seed samples were taken for essential analysis. When plants growth completed, each plot was harvested separately then canola yield and also the phosphorus, iron and zinc content of shoots and grain were measured.
The results of two years indicated that the treatments had no significant effects on pH and bicarbonate of soil while increasing sulfur application rate, caused a decrease in soil bicarbonate content. In addition to that, the treatments did not affect the yield of canola significantly. In the first year of experiment, treatments had shown significant effects (P=0.01) on glucosinolates, seed sulfur and Cu of leaf, whereas no effect determination was occurred about indices of leaf and seed of canola. the results also suggested an increase of 800 kg in the sixth treatment (600 kg sulfur consumption without Thiobacillus) and canola seed yield of treatment T6 enhancedfrom 3446 kg to 4531 kg per ha. Fertilization treatment (T8) could not increase canola yield, so it confirms that the nutrient concentration in experiment sites were near the critical level for canola.
In total results revealed that different sulfur treatments have no significant and considerable impacts on canola yield and soil chemical properties, and the effects was not observed in the second year of experiment, too. Probably the sulfur consumed or sulfur oxidation in the experiments was not enough to cope with high lime (14%) and buffering capacity of the soil. Also probably the nutrient concentration in test sites were more than critical level for canola and plants absorbed enough nutrients from the soil. No increase in canola yield in fertilization treatments (T8) can confirm this opinion, though. It also seems that there were no favorable conditions (soil moisture) for the oxidation of sulfur in the soil.