Document Type : Research Article
Authors
1
Soil and Water Research Institute, Agricultural Research Education and Extension Organization (AREEO), Karaj, Iran
2
Soil and Water Research Department, Mazandran Agricultural and Natural Resources Research and Education Center (AREEO), Sari, Iran
10.22067/jcesc.2026.97959.1447
Abstract
Introduction
Canola is a major oilseed crop in Iran. Producing high and stable yields with good quality requires balanced nutrient supply, particularly magnesium. Magnesium plays main role in photosynthesis, chlorophyll synthesis and phloem transport of assimilates. In intensive cropping systems, fertilizer management in farmers’ fields is mainly focused on nitrogen, phosphorus and potassium. Magnesium removal at harvest, along with strong K–Mg antagonism in the rhizosphere and at root uptake sites, predisposes crops to latent or overt magnesium deficiency and associated yield losses. Field surveys in canola-growing regions have shown that in a considerable proportion of fields, available magnesium is below 200 mg kg⁻¹ and the Mg/K ratio is less than one, conditions that substantially increase the risk of magnesium deficiency despite moderate to high total Mg reserves.
Materials and Methods
A multi-location field experiment was conducted over two growing seasons (2022–2023 and 2023–2024) at three research stations in Mazandaran (Gharakhil, Dashtnaz and Baykola) to assess the response of canola (cv. Zafar) to soil and foliar magnesium fertilization in soils differing in K/Mg ratio. The experiment was arranged as a factorial in a randomized complete block design with three replications, comprising three rates of soil-applied magnesium sulfate (0, 50 and 150 kg ha⁻¹, incorporated before sowing) and two foliar spray (0 and 5 g L⁻¹ magnesium sulfate applied at the stem elongation stage). The sites differed in physicochemical properties and in the concentration and ratio of ammonium acetate–extractable potassium and magnesium, thereby establishing. All other nutrients (N, P, S, and micronutrients) were supplied according to pre-plant soil testing and local recommendations so that magnesium remained the principal experimental factor. At the pre-budding stage, five plants per plot were harvested at ground level to determine shoot dry weight and the concentrations of magnesium, potassium and sulfur in the aboveground biomass. At physiological maturity, plant height, pods per plant, thousand-seed weight and seed yield were measured. Data were subjected to analysis of variance using SAS 9.4, treatment means were separated by Duncan’s test at the 5% probability level, and Pearson correlation coefficients were calculated to quantify relationships among nutritional traits, growth variables and yield.
Results and Discussion
Among locations, Dashtnaz (K<Mg) produced the highest shoot dry weight (366 g per five plants) and shoot magnesium concentration (≈0.365%), whereas Gharakhil (high CaCO₃ in the soil) showed the lowest biomass and shoot magnesium, and Baykola exhibited intermediate K/Mg status and growth. I n mean of 3 sites, the combined application of 150 kg ha⁻¹ soil magnesium plus foliar spraying increased shoot dry weight by 45–65% relative to the control.
Location effects on seed yield revealed that Baykola and Dashtnaz, despite contrasting patterns in pods per plant and thousand-seed weight, out yielded Gharakhil. At Gharakhil, greater plant height and more pods did not translate into higher yield, most likely because an unbalanced K/Mg ratio and potassium limitation constrained stomatal conductance, assimilate transport and grain filling. In Baykola, increasing soil applied magnesium from 0 to 50 and 150 kg ha⁻¹ raised seed yield from 2996 to 3451 and 3831 kg ha⁻¹, whereas combining higher applied rates with foliar application reduced yield, indicating the existence of an optimum magnesium level beyond which marginal returns decline or negative ionic interactions. At Dashtnaz, maximum yield was obtained with 50 kg ha⁻¹ magnesium; higher rates mainly stimulated vegetative growth without significant additional yield, consistent with a saturation response under relatively Mg sufficient conditions. In mean of 3 sites correlation analysis showed that seed yield was most strongly and positively associated with pre flowering shoot dry weight (r≈0.60**), followed by pods per plant (r≈0.22*) and shoot magnesium concentration (r≈0.22*), and was negatively correlated with shoot potassium and sulfur concentrations. These relationships emphasize the main roles of early biomass accumulation, sink size and adequate magnesium status in supporting yield formation.
Conclusion
Soil and particularly foliar magnesium applications significantly increased shoot dry weight and shoot magnesium concentration and, relatively balanced K/Mg, enhanced sink capacity (pods per plant) and seed yield. At Baykola, 50 kg ha⁻¹ magnesium sulfate combined with foliar spraying at stem elongation stage increased yield by about 15% over the control and represents a practical, cost effective fertilization strategy, whereas 150 kg ha⁻¹ mainly promoted vegetative growth with reduced marginal yield response. At Dashtnaz, 50 kg ha⁻¹ magnesium without foliar application was sufficient for high yield, and higher applied rates chiefly increased biomass without yield increase, while at Gharakhil the limited yield response to magnesium indicates that correcting the K/Mg ratio and ensuring adequate potassium supply must precede higher magnesium inputs. Overall, site specific magnesium management centered on an approximate optimum of 50 kg ha⁻¹, combined with monitoring and adjustment of the K/Mg ratio and recognition of sulfur’s secondary role under these conditions, can improve yield, fertilizer use efficiency and the sustainability of canola production in Mazandaran Province.
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