Effect of calcium level on growth and nitrogen metabolism of Welsh onion

Objectives The effect of calcium (Ca) on growth and nitrogen metabolism of Welsh onion ( Allium fistulosum L.) was investigated to clarify the role of Ca in improving the yield and quality, and provide a theoretical basis for the optimization fertilization technique.

Methods Welsh onion cultivars ‘Zhaohe’and ‘Zhangqiu’ were used as test materials in sand cultural and feild trails. Four Ca²⁺ levels of 0, 4, 6, 8 mmol/L in sand cutural trail and four CaO application rate of 0, 225, 450, 675 kg/hm² in field trail were designed. Different forms of nitrogen and activities of nitrate reductase (NR), glutamine synthetase (GS), glutamate synthase (GOGAT), glutamate dehydrogenase (GDH) in onion leaves were determined during seedling over-summer stage (Jul. 17), vigorous growth stage (Sept. 11) and cauloid forming stage (Oct. 20). The growth, yield and quality of Welch onion were measured at harvest stage (Nov. 13).

Results With the increase in solution Ca level, plant height, cauloid diameter of potted Welsh onion as well as root and shoot fresh weight were increased significantly, and reached peak in 6 mmol/L Ca level with biomass per plant of 211.13 g. Continue increase to 8 mmol/L, the biomass significantly decreased to 185.83 g. ‘Zhangqiu’ showed significantly higher plant height, cauloid diameter and shoot fresh weight compared to ‘Zhaohe’, while the root fresh weight was not the case. Appropriate Ca application enhanced the activities of GOGAT, GDH, NR and GS dramatically in Welsh onion leaves particularly in the most sensitive vigorous growth stage. The content of NH₄⁺-N, NO₃^--N, soluble protein and free amino acid increased with growth stage and reach peak at vigorous growth stage. All the quality-related indexes of two cultivars were highest at 6 mmol/L Ca level, the yield of ‘Zhangqiu’ and ‘Zhaohe’ was significantly increased by 79.94%, 74.42% in 6 mmol/L, respectively, compared to the control. For the field trial, the yields in treatment with CaO of 450 kg/hm² were increased by 12.30%, 19.00%, respectively.

Conclusions The appropriate application of Ca can enhance the growth, improve enzyme activities of nitrogen metabolism and the contents of different nitrogen forms of Welsh onion, therefore the yield and quality. Comprehensively, the nutrient solution containing Ca of 6 mmol/L and soil CaO supplying at 450 kg/hm² are the most conducive to improve the growth, quality and yield of Welsh onion.