Combine effect of nitrogen and humic acid on carbohydrate-nitrogen ratio, photosynthetic activities, fruit yield and quality of ‘kinnow’ mandarin

Abstract

The ability of plants to produce high fruit yield and quality depends on the utilization of reserved carbohydrates and photosynthetic activity of plants at initial stages of bud sprouting and flowering. Optimum dose of N is essential for this mechanism. Therefore, different doses of N (600, 900 and 1200g per plant) along with 120 mL of 8% humic acid (HA) per plant were applied in three equal installments (before flowering, after fruit setting and fruit development stages). Growth parameters, C:N ratio, photosynthetic activities and their effects on yield and quality of ‘Kinnow’ fruit of these plants were compared with the control plants receiving recommended dose of N (1200g) applied in two equal installments (before flowering and at fruit setting). Source of fertilizers for nitrogen, phosphorus and potassium and method of their application was kept same in all treatments. Results revealed that plants receiving N dose of 900g with 120 ml of 8% humic acid showed the best utilization of carbohydrates which was also found directly correlated with photosynthesis. This treatment depicted increase in photosynthesis and maintenance in C:N ratio of plant at fruit setting stage. It was noted that maintenance of carbohydrates at flowering time, during fruit setting and harvesting stages (13.51, 13.44 and 13.39%, respectively) showed promising results on fruit development (956 fruit per plant) and quality of Kinnow. Maximum TSS (12.20 °Brix), ascorbic acid (44.96mg100g-1), total sugars (13.69%), phenolic compounds (398.5mg GAE100g-1) and antioxidants (90.13 Ic µgL-1) were also recorded in the fruits of plant treated with 900g N and 120 mL HA. The dose of N (900g and 120mL HA) in three equal splits (before flowering, fruit setting and fruit maturation) along with recommended doses of P and K (each 600g per plant) were found effective to build synergism between photosynthetic and C:N ratio which resulted in enhancing fruit yield and quality of ‘Kinnow’ mandarin.