Multi-objective optimization of water and nitrogen regimes for drip-fertigated sugar beet in a desert climate

Abstract

The scarcity of water resources and low water-nitrogen use efficiency largely restrict the sustainable development of sugar beet ( Beta vulgaris L.) in desert climates. A three-year field experiment was conducted to investigate the responses of taproot yield, sucrose content, sugar yield, irrigation water use efficiency, nitrogen partial factor productivity, soil nitrate nitrogen residue and economic benefit of drip-fertigated sugar beet under plastic mulch to varying water and nitrogen supplies. There were three irrigation levels (W 0.6 : 0.60 ET c , W 0.8 : 0.80 ET c and W 1.0 : 1.00 ET c in 2019 and 2020; and W 0.4 : 0.40 ET c , W 0.6 : 0.60 ET c and W 0.8 : 0.80 ET c in 2021, where ET c is the crop evapotranspiration) and six nitrogen (N) application rates (N 25 : 25 kg N ha −1 , N 60 : 60 kg N ha −1 , N 120 : 120 kg N ha −1 , N 240 : 240 kg N ha −1 , N 360 : 360 kg N ha −1 and N 480 : 480 kg N ha −1 ). The combined evaluation model based on the overall difference was further used to explore the optimal combination of irrigation amount and N rate for multi-objective optimization. The results showed that there was no significant difference in sucrose content among the irrigation treatments in the same year. Taproot yield, sugar yield, irrigation water use efficiency of both taproot yield and sugar yield increased and then generally stabilized with the increasing N rate under the same irrigation amount. Nitrogen partial factor productivity of both taproot yield and sugar yield decreased with the increase of N rate. There was no significant difference in soil nitrate nitrogen residue among the irrigation treatments under N 25 , N 60 and N 120 , but increasing N rate increased the soil nitrate nitrogen residue. Net return first increased and then decreased as N rate increased under the same irrigation amount. Based on the combined evaluation model, the multi-target optimization was obtained under W 0.6 N 120 . The results indicated that the combination of irrigation amount of 0.60 ET c and N rate of 120 kg N ha −1 was benifical for the sustainable production of drip-fertigated sugar beet in desert climates. • The combined evaluation model was used to for multi-objective optimization of water and nitrogen regimes. • Maximum sugar yield and net return were obtained under 80 % crop evapotranspiration and 120 kg N ha −1 . • Taproot/sugar yield and irrigation water use efficiency increased and then stabilized with increasing nitrogen rate. • Multi-target optimization was obtained under 60 % crop evapotranspiration and 120 kg N ha −1 for drip-fertigated sugar beet.