Integrated water and fertilizer management is important for promoting sustainable development of facility agriculture, and biochar plays an important role in guaranteeing food production, as well as alleviating water shortages and the overuse of fertilizers. The field experiment had twelve treatments and a control (CK) trial including two irrigation amounts (I1, 100% ETm; I2, 60% ETm; where ETm is the maximum evapotranspiration), two nitrogen applications (N1, 360 kg ha-1; N2, 120 kg ha-1) and three biochar application levels (B1, 60 t ha-1; B2, 30 t ha-1 and B3, 0 t ha-1). A multiobjective synergistic irrigation-nitrogen-biochar application system for improving tomato yield, quality, water and nitrogen use efficiency, and greenhouse emissions was developed by integrating the techniques of experimentation and optimization. First, a coupled irrigation-nitrogen-biochar plot experiment was arranged. Then, tomato yield and fruit quality parameters were determined experimentally to establish the response relationships between irrigation- nitrogen-biochar dosage and yield, comprehensive quality of tomatoes (TCQ), irrigation water use efficiency (IWUE), partial factor productivity of nitrogen (PFPN), and net greenhouse gas emissions (NGE). Finally, a multiobjective dynamic optimization regulation model of irrigation-nitrogen-biochar resource allocation at different growth stages of tomato was constructed which was solved by the fuzzy programming method. The results showed that the application of irrigation and nitrogen to biochar promoted increase in yield, IWUE and PFPN, while it had an inhibitory effect on NGE. In addition, the optimal allocation amounts of water and fertilizer were different under different scenarios. The yield of the S1 scenario increased by 8.31% compared to the B1I1N2 treatment; TCQ of the S2 scenario increased by 5.14% compared to the B2I2N1 treatment; IWUE of the S3 scenario increased by 10.01% compared to the B1I2N2 treatment; PFPN of the S4 scenario increased by 9.35% compared to the B1I1N2 treatment; and NGE of the S5 scenario decreased by 11.23% compared to the B2I1N1 treatment. The optimization model showed that the coordination of multiple objectives considering yield, TCQ, IWUE, PFPN, and NGE increased on average from 4.44 to 69.02% compared to each treatment when the irrigation-nitrogen-biochar dosage was 205.18 mm, 186 kg ha-1 and 43.31 t ha-1, respectively. This study provides a guiding basis for the sustainable management of water and fertilizer in greenhouse tomato production under drip irrigation fertilization conditions.
