Growth, Nitrate Accumulation, and Macronutrient Concentration of Pakchoi as Affected By External Nitrate-N: Amino Acid-N Ratio

ABSTRACT

A study was carried out to determine the influence of nitrogen (N) sources on the growth, nitrate (NO₃ ⁻) accumulation, and macronutrient concentrations of pakchoi (Brassica chinensis L.) in hydroponics. Plants were supplied with NO₃ ⁻ and two amino acids (AA), glutamic acid (Glu), and glutamine (Gln), at six NO₃ ⁻-N/AA-N molar ratios: (1) 100:0, (2) 80:20, (3) 60:40, (4) 40:60, (5) 20:80, (6) 0:100. The total N concentration was 12.5 mmol/L for all treatments in nutrient solutions. Both AAs reduced plant growth with decreasing NO₃ ⁻-N/AA-N ratios, but the reduction was for Gln than for Glu. At 80:20 NO₃ ⁻-N: Gln-N ratio, the Gln had no significant effect on pakchoi fresh weights. Decreasing NO₃ ⁻-N/AA-N ratios reduced NO₃ ⁻ concentrations in the plant, regardless of AA sources. Adding an appropriate portion of AA-N to nutrient solutions for hydroponic culture increased concentrations of N, phosphorus (P), and potassium (K) in pakchoi shoots. Substituting 20% or less of NO₃ ⁻-N with Gln-N in hydroponic culture will increase the pakchoi quality by reducing NO₃ ⁻ concentration and increasing mineral nutrient concentrations in shoots without significant reduction of crop yields.

Keywords:

• NO₃ ⁻-N
• amino acid-N
• NO₃ ⁻ accumulation
• growth
• macronutrient concentration
• pakchoi

ACKNOWLEDGMENTS

This study was supported by the National Natural Science Foundation of China (No. 30370838), the National Key Basic Research Special Funds of China (G1999011707), and the Science and Technology Committee of Zhejiang Province of China (No. 021102084).

Notes

∗significant at P < 0.05. NS: not significant.