Interactive effects of irrigation and exponential fertilization on nutritional characteristics in Populus x euramericana cv. '74/76' cuttings in an open-air nursery in Beijing, China

Nutritional characteristics determine tree stock quality to a considerable extent. Exponential fertilization can induce nutrient reserves within juvenile trees, but its validity on poplar is contingent on interaction with a scientific irrigation regime due to limited water resources under global warming. In the present study, we raised 3200 Populus x euramericana cv. '74/76' cuttings under four irrigation regimes of 0 (I0), 60 % (I60), 80 % (I80), and 100 % (I100) of field capacity for soil moisture content with or without (control) the employment of nitrogen (N) addition delivered as exponential fertilization at the rate of 8 g N cutting(-1) (E8) in an open-air nursery in Beijing, China. Both height and diameter increased with the increment of soil moisture ratio or in response to exponential fertilization (EF) without any interactive effects. In general, concentrations of N, phosphorus (P), and potassium (K) declined with time in stem but foliar N concentration did not change. Under the I100 regime, EF increased foliar N concentration relative to the control but failed to affect N concentration in stem in September, when both N concentration and N content were increased by EF under the I80 regime. Stem-K content and concentration by EF under the I80 regime also increased in September, therefore EF-treated cuttings had a higher ratio of K content in stem to that in whole plant (%ANAR). Vector diagnosis for nutritional status indicated that EF resulted in dilution of K concentration but induced a steady-state P uptake in leaves under all irrigation regimes. Therefore, EF of N addition could promote N uptake to leaves of P. x euramericana cv. '74/76' cuttings, but it had a null effect on N and P reserves in stem and impaired K reserves. In conclusion, the irrigation regime of 80 % field capacity of soil moisture content was suggested for the culture of juvenile P. x euramericana cv. '74/76' cuttings. As the interactive meaning, EF was also suggested for its excellent promotion on both N and K uptakes.