Precise fertilization is often required for greenhouse vegetables in modern agriculture. However, conventional fertilization can rely mainly on the subjective experience. In this study, a systematic investigation was implemented to determine the relationship between leaf dry matter content and leaf phosphorus concentration in tomatoes. The field experiments were carried out under different phosphorus supply levels. A dilution curve model was then established, according to the leaf dry matter and phosphorus concentration data. A diagnostic analysis of the phosphorus nutritional status was constructed to recommend the fertilization amount for tomatoes. Both theoretical and practical guidance were provided for the phosphorus nutrition and supply in the substrate-cultivated tomato. The Jinpeng ‘101’ tomato variety was used as the plant material. Five levels of the phosphorus supply (0, 40%, 80%, 100%, and 140%) were designed according to the standard Yamasaki tomato nutrient solution formula. A systematic analysis was made to explore the effect of the phosphorus supply on the leaf dry matter content, leaf phosphorus concentration, phosphorus absorption, and single fruit weight, yield, and fruit quality. Dilution curve models were then established to determine the critical phosphorus concentration, critical phosphorus absorption, and phosphorus nutrition index (PNI) for greenhouse tomato. The analytic hierarchy process and entropy weight coefficient were used to determine the subjective and objective weights. Then, the tomato growth indicators were evaluated to combine with the technique for the order preference by similarity to ideal solution (Topsis) and entropy theory. Various growth indicators were also obtained to integrate with these weights using game theory. The evaluation scores were non-linearly fitted with the PNI in order to validate the accuracy of the PNI model. The results showed that the leaf dry matter content of the tomatoes significantly increased with the higher phosphorus supply levels, indicating that the appropriate phosphorus supply promoted the tomato growth. Furthermore, the leaf phosphorus concentration decreased gradually as the growth stage progressed. But the leaf phosphorus concentration shared an increasing trend at the higher phosphorus supply levels, indicating the essential role of phosphorus in tomato growth. Phosphorus absorption by tomato leaves also increased with the higher phosphorus supply levels, indicating a close relationship between phosphorus absorption and fertilization. In terms of the model construction, the critical phosphorus concentration dilution curve model demonstrated high accuracy, with a root mean square error (RMSE) of less than 0.04973 and a normalized RMSE (n-RMSE) of less than 10.334%. The strong stability and high predictive precision greatly contributed to the reliable theoretical basis for the phosphorus nutrition management in tomato. Phosphorus nutritional diagnosis with the PNI model showed that the 0 and 40% phosphorus supply treatments exhibited significant phosphorus deficiency, with the PNI values being below 1. The tomato growth was also limited by phosphorus. The PIN values were close to 1 in the 80% and 100% phosphorus supply treatments, indicating sufficient phosphorus nutrition with no significant growth limitations. The 140% phosphorus supply treatment (excess phosphorus) shared the PNI values greater than 1, indicating that the excessive phosphorus supply was negatively correlated to the tomato growth. Nonlinear fitting of PNI was evaluated among the treatments. The best performance was achieved in the 100% phosphorus supply. In the Guanzhong area of Shaanxi Province, the phosphorus supply was recommended for the substrate-cultivated tomatoes in spring and autumn greenhouse as follows: The phosphorus supply levels were 9.369, 25.292, and 18.743 kg/hm² (spring) and 9.680, 12.240, and 5.997 kg/hm² (autumn), respectively, at the seedling, flowering and fruit-setting, and maturity stages. These phosphorus supply levels were aligned with the various growth indicators of tomatoes. The finding can also provide scientific support to optimize the phosphorus management in tomato production.

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.

Microbial activities are the dynamic core of nutrient cycling in organic substrates, and the exploitation of plant growth-promoting rhizobacteria strains contributes to sustainable agricultural development. This study aimed to investigate the effect and mechanism of Bacillus velezensis SX13 in nutrient cycling and plant promotion under different substrate supply conditions. The effects of reduced substrate amount (sCK) and inoculation of SX13 strain under both substrate supply conditions (Bv and sBv) on rhizosphere microenvironment and plant growth were investigated using conventional substrate amount (CK) as a control. Results showed no significant difference in the α-diversity indexes (Chao1 and Shannon) of the rhizospheric microbial community among the four treatments. However, nonmetric multidimensional scaling analysis and principal coordinate analysis revealed that compared with CK treatment, the inoculation of SX13 strain and reduced substrate supply reshaped the β-diversity structure of microbial communities. Furthermore, inoculation with B. velezensis SX13 under both substrate supply conditions increased the abundance of Proteobacteria (1.64%–2.46%), Acidobacteria (14.09%–43.07%), and Firmicutes (179.29%–861.29%). The results of the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis showed that the metabolic pathway with the highest abundance of enriched genes was also the pathway with the most enriched differential genes caused by reducing substrate supply or inoculation of B. velezensis SX13. The rhizosphere inoculation of B. velezensis SX13 significantly up-regulated the top genes related to carbohydrate esterases, carbohydrate binding modules, glycoside hydrolases, glycoside transferases, and polysaccharide lyases. As a result, the activities of carbon and nitrogen cycle-related enzymes such as cellobiohydrolase, β-glucosidase, urease, L-leucine amino peptidase, and β-1,4-N-acetylglucosaminidase were increased, which in turn accelerated nutrient cycling. B. velezensis SX13 and its mediated improvement of the rhizospheric microenvironment resulted in the up-regulation of root CsNRT family genes (such as CsNRT1.1, CsNRT1.4a, CsNRT1.4b, CsNRT1.5a, CsNRT1.5b, CsNRT1.5c, and CsNRT1.8), which accelerated nitrogen uptake, accumulation, and utilization efficiency and ultimately improved the yield and quality of cucumber. The effect of SX13 strain was more stable and efficient under conventional substrate supply conditions than under reduced substrate supply conditions.