[Effects of water and nitrogen coupling under furrow irrigation on tree growth, absorption and utilization of water and nitrogen of ].

We explored the coupling effects of water and nitrogen in furrow irrigation on the growth and absorption and utilization of water and nitrogen in young poplar trees (triploid ), under three irrigation levels (W, W, W; when the soil water potential of 40 cm under the ditch reaches -20, -33 and -45 kPa respectively, irrigate), four N application levels (N, N, N and N; the fertilization amount was 120, 190, 260 and 0 kg·hm·a), and natural conditions (CK). Based on the growth status of trees, the optimal combination of irrigation level and nitrogen application rate under furrow irrigation conditions was determined. The results showed that WN (high water and low fertilizer; soil water potential threshold for initiating irrigation was -20 kPa and N application rate was 120 kg·hm·a) had the strongest effect on the stand productivity, with a value of 33.37 m·hm·a. The significant coupling effect of water and N was detected only for tree height and total individual biomass. The increase of both irrigation amount and N application rate could increase the amount of N uptake, being mainly affected by the latter. The total amount of N uptake was the highest in the WN treatment and reached 112.17 kg·hm·a, being 74.0% higher than that in CK. Among all the treatments, N uptake efficiency and N fertilizer partial productivity of WN were the highest and significantly higher than those of the other treatments. The N uptake efficiency of the whole plant, aboveground part, and belowground part reached 36.8%, 28.5% and 6.4% in the WN treatment, and its total N partial productivity reached 221.4 kg·kg. The effect of irrigation amount under different water-nitrogen coupling treatments on the irrigation water use efficiency was significant. Among them, irrigation water use efficiency in WN was the highest and reached 13.66 g·kg. WN had the highest water uptake amount and efficiency, which were 13268.28 t·hm and 129.4%, respectively. To achieve great benefits, adequate irrigation (-20 kPa) and relatively low N application rate (120 kg·hm·a) should be selected during the young growth of the triploid .