Boron deficiency may be widespread in Brassica oleracea var. capitata L. in Lao Cai Province, North Western Vietnam

Cabbage (Brassica oleracea var. capitata L.) is widely grown in the highlands of North Western Vietnam, and foliar analysis of 18 crops in the Bac Ha district, and 9 in the Sa Pa district of the Lao Cai Province, revealed low mean concentrations of boron (B, 15.6 mg kg⁻¹), and copper (Cu, 4.8 mg kg⁻¹). In three following field experiments, B treatments generally increased foliar B concentrations and growth, whereas Cu treatments affected neither growth nor the foliar Cu concentration. For the three experiments, the relative treatment yield within an experiment, and its foliar B concentration, define a critical concentration of 8–10 mg B kg⁻¹. That is, B deficiency seasonally limits cabbage yields in Lao Cai Province, and liming increases the deficit. Soil applications of B and Cu are inexpensive and effective, but repetition should be justified by foliar analysis. Lastly, excess N was applied to more than half of the cabbage crops, with potentially deleterious impacts on shelf-life, human health, and the environment.