Effects of nitrogen forms and ratios on photosynthetic characteristics of Newhall navel orange in calcareous yellow soils
-
Abstract
A pot experiment was conducted in a rain-light shad to provide scientific basis for citrus nitrogen nutrient and fertilizer management via analysis of the effects of different nitrogen forms and ratios NO3--N∶NH4+-N at 100∶0 (CaNO3·4H2O 42.16 g·pot-1), NO3--N∶NH4+-N at 75∶25 (CaNO3·4H2O 31.62 g·pot-1 and NH4HCO3 7.06 g·pot-1), NO3--N∶NH4+-N at 50∶50 (CaNO3·4H2O 21.08 g·pot-1 and NH4HCO3 14.12 g·pot-1), NO3--N∶NH4+-N at 25∶75 (CaNO3·4H2O 10.54 g·pot-1 and NH4HCO3 21.19 g·pot-1), and NO3--N∶NH4+-N at 0∶100 (NH4HCO3 28.25 g·pot-1 or CO(NH2)2 10.71 g·pot-1). Also the daily changes in photosynthetic rates (Pn), photosynthetic pigments (Chal. a, Chl. b, Car.) contents, light compensation point (LCP) and light saturation point (LSP) of Newhall navel orange grafted in trifoliate orange were analyzed. The results showed that under the mixed dose of NO3--N and NH4+-N at the ratio of 75∶25, contents of Chl. a, Chl. b and Car. and Pn were significantly higher than those under other nitrogen sources treatments. Pn, Tr, WUE and Gs of Newhall navel orange at 10:00 reached highest values with 4.81 μmol(CO2)·m-2·s-1, 2.30 mmol(CO2)·m-2·s-1, 2.09 and 0.09 mol·m-2·s-1, respectively. The contents of Chl. a, Chl. b and Car., and Pn , Tr, WUE and Gs all decreased with increasing NH4+-N/NO3--N ratio. Under sole NO3--N (NO3--N∶NH4+-N=100∶0), Pn was 3.53 μmol(CO2)·m-2·s-1, significantly lower than that under mixed NO3--N and NH4+-N dose (NO3--N∶NH4+-N=75∶25). Under the sole CO(NH2)2, the contents of Chl. a, Chl. b and Car. and Pn were lowest, and Pn was only 3.07 μmol(CO2)·m-2·s-1. No significant differences were noted in Newhall navel orange Pn under the sole NH4+-N and CO(NH2)2. Also no significant differences were noted in LCP and LSP of Newhall navel orange among different nitrogen resources treatments. Both points were respectively maintained at 861.51 μmol·m-2·s-1 and 10.09 μmol·m-2·s-1. Mixed dose of NO3--N and NH4+-N at the ratio of 75∶25 was beneficial to Newhall navel orange in terms of Pn improvement.
-
-
DownLoad: