Optimal combination of substrate supply amount coupled with nutrient solution management program for cucumber planting

Substrate and nutrient supply are essential for vegetable cultivation in greenhouse. The strategies for plant nutrient supply vary depending on the cultivation methods or substrate dosages employed. With the development of mechanization, wide-row spacing substrate cultivation became an optimize mode of the greenhouse cucumber cultivation, aligning with the trend of intelligent agriculture. To determine the optimal nutrient solution supply amount (NS) and supply frequency (SF) for promoting the integrated growth of cucumber under wide-row spacing substrate cultivation, we explored the effects of substrate supply amount (SS), NS, and SF on cucumber yield, quality, and element utilization efficiency. A five-level quadratic orthogonal rotation combination design with three experimental factors (NS, SF, and SS) was implemented for 23 coupling treatments over three growing seasons, including spring (2022S and 2023S) and autumn (2022A). The technique for order preference by similarity to ideal solution (TOPSIS) combining weights based on game theory was applied to construct cucumber comprehensive growth evaluation model. Single and two experimental factors analyses revealed significant effects of single factors and the coupling of NS−SS, NS−SF and SS−SF on the integrated growth of cucumber for all three growing seasons. For the NS−SF−SS combination, the optimal parameters for comprehensive cucumber growth were determined as follows: levels of −1.68 for NS, −0.7 for SF, and −1.682 for SS in 2022A; −0.43 for NS, −0.06 for SF, and 0.34 for SS in 2022S; 0.3 for NS, −0.02 for SF, and 0.04 for SS in 2023S. Furthermore, for SS ranges of 2.00–3.01, 3.01–4.50, 4.50–5.99, 5.99–7.00 (L · plant −1 ), the corresponding NS and SF intervals maximizing cucumber integrated growth in spring were: 0.28–0.30 (L · plant −1 ) and 6 (times · d −1 ), 0.26–0.30 (L · plant −1 ) and 6 (times · d −1 ), 0.25–0.30 (L · plant −1 ) and 6 (times · d −1 ), 0.23–0.30 (L · plant −1 ) and 6 (times · d −1 ), respectively. With the same SS, the corresponding NS and SF intervals that maximized cucumber integrated growth in autumn were: 0.10 (L · plant −1 ) and 8 (times · d −1 ), 0.18 (L · plant −1 ) and 7 (times · d −1 ), 0.30 (L · plant −1 ) and 6 (times · d −1 ), 0.49 (L · plant −1 ) and 5 (times · d −1 ), respectively. The results provide a theoretical basis for solution management, and further in-depth research on cucumber cultivation.