Effect of magnesium fertilization on seed yield, seed quality, carbon assimilation and nutrient uptake of rapeseed plants

Magnesium (Mg) deficiency is becoming an important mineral nutrient deficiency in intensive crop production systems due to large removal of Mg from soils as well as imbalanced nutrition with Mg. In this study, rapeseed (Brassica napus L.) plants were grown in six locations with various soil and growth conditions along the Yangtze River Basin which is one of the largest rapeseed-producing areas in the world. Six application rates of Mg (i.e., from 0 to 45 kg Mg ha−1) were used to study the responses of i) seed yield and yield components, ii) seed oil and fatty acids, iii) leaf and pod carbon assimilation, iv) nutrient uptake and v) germination of seeds harvested from plants with different Mg fertilization. Increasing Mg fertilization greatly increased seed yield of the rapeseed plants in all studied locations. The visual Mg deficiency symptoms were observed in all field locations without Mg applications. The number of pods per plant was the most strongly affected yield component by the Mg fertilization. The largest increases in seed yield by Mg were found in the locations where the soil extractable Mg and K concentrations were 28.1 mg kg−1 and 279.5 mg kg−1, respectively. The carbon assimilation of the leaves and pods and the amount of oil and unsaturated fatty acids of the seeds were positively affected by Mg fertilization. Improving Mg nutritional status of plants also enhanced the total uptake of nitrogen and phosphorus, but not the potassium uptake. The germination capacity of the seeds from the plants with adequate Mg nutrition was better than the seeds from the plants without Mg application. This study conducted under field conditions with various soil and environmental conditions showed clearly that improving Mg nutritional status of plants significantly contributed to the seed yield, seed quality and seed vigour (germination) as well as increased uptake of nitrogen and phosphorus in rapeseed plants.