| Summary: | Clarifying the optimal combination of N fertilizer application rate and application method can maximize the yield of drip-irrigated sugar beet in arid areas, which is of great significance for reducing farmland N pollution and achieving sustainable agricultural development. In this three-year field experiment in Xinjiang, China, the effects of three N application rates [75 kg ha<sup>−1</sup> (N1), 150 kg ha<sup>−1</sup> (N2), and 225 kg ha<sup>−1</sup> (N3)] and three N application methods [the proportion of N applied at canopy rapid growth stage, taproot expansion stage, and sugar accumulation stage were (M<sub>1</sub>) 100%: 0%: 0%, (M<sub>2</sub>) 70%: 30%: 0%, and (M<sub>3</sub>) 50%: 30%: 20%] on the dry matter accumulation (DMA) and distribution, leaf senescence, yield, and agronomic N use efficiency (aNUE) of drip-irrigated sugar beet were explored. The results showed that N application (N1, N2, and N3 treatments) increased the shoot DMA by 27.7% (three-year average), 52.6%, and 83.1%, and the taproot DMA by 28.3%, 43.2%, and 61.6%, respectively (<i>p</i> < 0.05), compared with CK (no N supply) treatment. The N application methods M<sub>2</sub> and M<sub>3</sub> increased the shoot DMA by 5.6% (three-year average) and 1.0% (<i>p</i> > 0.05), respectively, and the taproot DMA by 7.2% and 3.6% (<i>p</i> < 0.05), respectively, compared with M<sub>1</sub>. In addition, M<sub>2</sub> could delay the end of shoot and taproot growth (t<sub>e</sub>) and the occurrence of maximum growth rate (t<sub>m</sub>). In particular, the N3M<sub>2</sub> treatment increased the leaf area index (LAI) by 20.4–75.9% (<i>p</i> < 0.05) compared with other treatments by increasing the leaf area duration (LAD) and decreasing the leaf senescence rate (LSR). The taproot yield and sugar yield of N3M<sub>2</sub> treatment reached the maximum at harvest time, but there was no significant difference in taproot yield and sugar yield between N3M<sub>2</sub> treatment and N2M<sub>2</sub> treatment. The aNUE in N2M<sub>2</sub> treatment was the highest (<i>p</i> < 0.05), which was 1.29–7.85 times higher than that of other treatments. Therefore, reducing the N application rate from 225 kg·ha<sup>−1</sup> to 150 kg·ha<sup>−1</sup> and applying 70% and 30% of 150 kg N ha<sup>−1</sup> at the canopy rapid growth stage and the taproot expansion stage, respectively, could achieve the goal of increasing sugar beet yield and N use efficiency. This study will provide an important reference for the sustainable production of sugar beet under drip irrigation in Xinjiang, China.
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