Optimization of irrigation and nitrogen fertilization increases ash salt accumulation and ions absorption of drip-fertigated sugar beet in saline-alkali soils

• Irrigation and nitrogen effects on dry matter, ash salt accumulation, irons uptake of sugar beet were explored. • Dry matter and ash salt accumulation, Na + , K + , Ca 2+ and Mg 2+ uptake of W 3 were smaller than those of W 1 and W 2 . • Ash salt accumulation, Na + , K + , Ca 2+ and Mg 2+ uptake were proportional to dry matter accumulation. • Binary quadratic equations were fitted between water-nitrogen inputs and dry matter, ash salt accumulation and irons uptake. Sugar beet ( Beta vulgaris L.), as a salt-tolerant plant, has been widely cultivated in saline-alkali soils, e.g. southern Xinjiang of China, due to its effective capability of reducing soil salinity. A two-year field experiment was conducted on drip-fertigated sugar beet under plastic mulch to explore to effects of three irrigation amounts (W 1 : 0.60 ET c , W 2 : 0.80 ET c and W 3 : 1.00 ET c , where ET c is the crop evapotranspiration) and six nitrogen application rates (N 1 : 25 kg N ha −1 , N 2 : 60 kg N ha −1 , N 3 : 120 kg N ha −1 , N 4 : 240 kg N ha −1 , N 5 : 360 kg N ha −1 and N 6 : 480 kg N ha −1 ) on sugar beet growth, ash salt accumulation, plant Na + , K + , Ca 2+ and Mg 2+ uptake. The results showed that the year and the two-way interaction of irrigation and nitrogen fertilization had significant effects on dry matter, ash salt accumulation, plant Na + , K + , Ca 2+ and Mg 2+ uptake, but there was no significant effect of the three-way interaction of year, irrigation and nitrogen fertilization on ash salt accumulation, plant Ca 2+ and Mg 2+ uptake. The dry matter, ash salt accumulation, Na + , K + , Ca 2+ and Mg 2+ uptake of N 1 were significantly lower than those of other treatments. Nitrogen fertilization increased the dry matter and ash salt accumulation, Na + , K + , Ca 2+ and Mg 2+ uptake of sugar beet. The ash salt, K + and Ca 2+ were mainly distributed in the leaf and petiole, while Na + and Mg 2+ were mainly distributed in the taproot. Among the four ions, the average contents of K + and Na + were larger in all treatments, which were 1.79 % and 1.62 % in the two years, respectively. The average content of Mg 2+ was 0.36 % in all treatments in the two years, and the average content of Ca 2+ was lowest in all treatments, which was 0.14 % in the two years. Compared to W 1 and W 2 , W 3 decreased the dry matter and ash salt accumulation, plant Na + , K + , Ca 2+ and Mg 2+ uptake. The ash salt accumulation, plant Na + , K + , Ca 2+ and Mg 2+ uptake increased with the increasing dry matter accumulation. Based on the response surface methodology, the relationships between water-nitrogen inputs and dry matter, ash salt accumulation, plant Na + , K + , Ca 2+ and Mg 2+ uptake were established. The results can provide a theoretical basis for the phytoremediation of sugar beet in southern Xinjiang of China and maybe elsewhere with similar arid and semi-arid climates.