Leaf gas exchanges and production of kale under Ca(NO₃)₂ concentrations in salinized nutrient solution¹

Trocas gasosas e produção em couve folha sob concentrações de Ca(NO₃)₂ em solução nutritiva salinizada

HIGHLIGHTS:

Salt stress decreases the photosynthetic process and yield of kale, regardless of the concentration of Ca(NO₃)₂.

Adequate calcium (between 1,000 and 1,300 mg L^-1) nutrition reduces salinity effect on gas exchanges.

Excess of Ca(NO₃)₂ (1,875 mg L^-1) increases the osmotic effect on gas exchanges, except the internal carbon concentration.

ABSTRACT

Adequate mineral supplementation can be a strategy to enable the use of brackish water in the production of vegetables. This study intended to evaluate the effect of calcium nitrate concentrations on leaf gas exchanges and yield of kale (Brassica oleracea L) fertigated with salinized nutrient solutions. The experiment was conducted in a randomized block experimental design (4 + 1), with four replicates. Four nutrient solutions prepared in brackish water (6.0 dS m^-1) containing four concentrations of Ca(NO₃)₂ [(750, 1,125, 1,500, and 1,875 mg L^-1)] and a control treatment (standard nutrient solution using low-salinity water, 0.5 dS m^-1 (750 mg L^-1 of Ca(NO₃)₂) were used in the study. The following analyses were performed: leaf gas exchanges, leaf area, and fresh matter yield. The standard nutrient solution promoted higher values for photosynthetic rate (13.06 µmol CO₂ m^-2 s^-1), stomatal conductance (0.19 mol H₂O m^-2 s^-1), transpiration (2.76 mmol H₂O m^-2 s^-1), instantaneous water use efficiency (4.73 mmol CO₂ mol^-1 H₂O), instantaneous carboxylation efficiency (0.053 mmol CO₂ mol^-1 CO₂), leaf area (2.78 cm² per plant), and leaf fresh matter yield (2.64 kg per plant). The Ca(NO₃)₂ not nullified but mitigated the deleterious effect of salt stress on leaf gas exchanges, except for kale yield (leaf fresh matter).

Key words:
Brassica oleracea L.; soilless; salt stress; calcium