Effects of Nitrogen, Phosphorus, Sulphur, Potassium, Calcium and Water Stress on Yield, Mineral and Amino Acid Composition, Dietary Fibre and Nutritive Value of Carrots

Abstract

In pot experiments with greatly differing rates of N, P, K and S, two levels of Ca and three levels of water, dry matter (DM) yields of carrot roots varied from 27 to 320 g pot⁻¹. Yields were reduced most by P and least by S deficiency. Total-N and NO₃-N concentrations varied from 0.56% to 1.98% and from 0 to 883 ppm in DM, respectively. Both N applications and K deficiency caused increases in total-N and NO₃-N. S applications increased total-S content from 0.056% to 0.120% in DM, of which between 61% and 30% was found in methionine + cystine. Total-N/total-S ratios decreased from 23 to 10 with S applications. Increasing P and K applications increased their content in DM twofold and fivefold, respectively. Iron, zinc, manganese and copper contents varied from 17 to 27, 15 to 35, 24 to 120 and 3.2 to 5.9 ppm in DM, respectively. Increasing N contents, whether due to N applications or nutrient or water stress, decreased the content (g per 16 g N) of essential amino acids in protein (%N 6.25). Only glutamic acid (glutamine) and arginine concentrations were increased. However, expressed as g per kg DM, the concentrations of all amino acids were positively correlated with protein content. Dietary fibre content was only slightly affected by the treatments. On average, the contents of soluble and insoluble dietary fibre were 9.2% and 12.2% in DM, respectively. In balance trials with rats, increasing protein concentrations of carrot DM increased the true digestibility of protein from 70% to 78%. Digestible energy and gross energy were also increased, from 73% to 83% and from 16.2 to 17.4 kJg⁻¹, respectively.

Key Words:

• cystine
• digestible energy
• methionine
• micronutrients
• N-balance in rats
• nitrate
• N/S ratios
• total-S