Effects of different fulvic acid application rates on fruit yield, quality and fate of 15N-urea in 'Red General' apple.

Abstract

To explore the effects of different fulvic acid application rates on 15N-urea absorption, utilization, residue amount, loss and fruit yield and quality, fifteen-year-old 'Red General'/ Malus micromalus Makino was selected as experiment material by using the 15N-labeled tracer technique. Five treatments were established: single urea (CK), combination of urea and fulvic acid with varied rates (NF1, NF2, NF3 and NF4 represented 75, 150, 300 and 450 kg·hm-2 fulvic acid application rates, respectively). The main results were as follows: the 15N derived from fertilizer (Ndff) in root, one-year-old branch and leaf were displayed with an order of NF3>NF4>NF2>NF1>CK at the fruit maturity stage, and significant difference was observed in Ndff value among the five treatments. The total N content and 15N absorption amount were highest in NF3, followed by NF4, and lowest in CK. Compared with CK, the 15N utilization rate in NF1, NF2, NF3 and NF4 was increased by 14.2%, 33.5%, 64.2% and 50.0%, and the 15N loss rate was decreased by 9.1%, 18.5%, 37.1% and 28.7% respectively. The residue amount of 15N-urea varied across different treatments, and that in 0-60 cm soil layer under combination of urea and fulvic acid was significantly higher than CK, with the highest value occurred in NF3, while it was lower than CK in 60-100 cm soil layer. In comparison with CK treatment, the largest increment of yield per plant and net income appeared in NF3, with an enhancement of 15.8% and 20.2%, respectively. In addition, the fruit hardness, soluble solid and sugar-acid ratio reached the highest value in NF3. Considering the responses of fruit yield and N utilization efficiency, the suitable fulvic acid application rate was 326.41-350.61 kg·hm-2.