Effects of magnesium chloride and magnesium sulfate on rapeseed yield and quality in red soil farmland

To evaluate the effects of magnesium chloride (MgCl₂) and magnesium sulfate (MgSO₄) on rapeseed yield and quality in red soil farmland, a two-site field experiment was conducted at Jinxian, Jiangxi Province, with three Mg fertilizer treatments (no Mg fertilizer, MgCl₂ and MgSO₄) in dryland and paddy fields from typical red soil areas between 2022 and 2023. Rapeseed yield and its components, biomass and Mg accumulation, seed oil, protein, sulfide content and fatty acid fractions were analyzed. The results show that compared with the control, MgCl₂ and MgSO₄ applied to red soil paddy fields and dryland can significantly increase rapeseed grain yields. Applying MgCl₂ and MgSO₄ increases the yield by 14.4% and 19.1% in red soil paddy fields, by 13.4% and 17.7% in red soil dryland, respectively. The yield gain of rapeseed is primarily attributed to the increase in pod number per plant with better enhancing effect of MgSO₄ than that of MgCl₂. Both application of MgCl₂ and MgSO₄ also significantly increases the biomass, magnesium content and magnesium accumulation in the above ground of rapeseed. MgSO₄ application exhibits a higher harvest index and magnesium fertilizer utilization rate. The yield of rapeseed in red soil dryland is slightly higher than that in red soil paddy fields, but the yield increase rate is lower than that in red soil paddy fields. The application of MgCl₂ and MgSO₄ as base fertilizers in both farmland increases the oil content and oleic acid content, reduces the erucic acid, stearic acid and palmitic acid content, and enhances the yield of oil and protein, thus improving rapeseed quality. MgSO₄ is better than MgCl₂ in improving the quality with better quality improvement effect in paddy fields. The application of MgCl₂ and MgSO₄ in both paddy fields and dryland of red soil all demonstrates a significant synergistic improvement effect on rapeseed yield and quality. The overall effect of MgSO₄ in increasing yield and quality is better than that of MgCl₂. It is recommended to choose MgSO₄ as the basal magnesium fertilizer in red soil paddy fields and dryland.