Objectives This study aimed to investigate the effects of pig blood-derived amino acid-chelated calcium (PC) on growth and fruit quality of tomato under salt stress conditions, in order to provide an effective technical measure for enhancing the resistance to saline stress and growth of crops, as well as to find a high-value utilization path of abundant pig blood resources.

Methods A pot experiment was conducted using a tomato cultivar "Dahong" as the test material. Four treatments were set up: CK (no salt stress + foliar spraying distilled water), NaCl (salt stress + foliar spraying distilled water), PC (salt stress + foliar spraying pig blood-derived amino acid chelated calcium), and CC (salt stress + foliar spraying calcium chloride). Tomato plants were harvested at the complete maturity of the third cluster fruits to measure indicators related to plant growth, photosynthesis, nutrient uptake, and fruit quality.

Results Compared with CK, NaCl treatments significantly reduced tomato biomass and fruit yield, while PC and CC treatments effectively alleviated the negative effects of salt stress. Compared with the NaCl treatment, PC and CC treatments significantly increased plant fresh weight by 15.5% and 1.8%, dry weight by 15.7% and 11.5%, leaf area by 19.7% and 12.7%, root surface area by 31.2% and 19.5%, and fruit yield by 42.7% and 13.6%, respectively. PC treatment significantly enhanced the N and K accumulations in roots, as well as the P and K accumulations in leaves, while CC treatment only significantly increased leaf P accumulation; PC treatment enhanced Chlorophyll a, chlorophyll b, and total chlorophyll contents by 30.5%, 76.9%, and 44.5%, respectively, increased net photosynthetic rate and stomatal conductance by 31.7% and 36.1%, respectively. In contrast, CC treatment only significantly increased the net photosynthetic rate; Additionally, PC treatment improved the firmness, color (L* value), and the transverse and longitudinal diameters of fruits. Compared with CK treatment, PC significantly increased soluble solids content in the second and third fruit clusters by 6.6% and 9.5%, soluble sugar content by 40.8% and 39.9%, enhanced sugar-acid ratio by 42.3% and 20.2%, respectively. Compared to NaCl treatment, PC further increased glutathione and ascorbic acid contents in the second and third fruit clusters and elevated Cd content in the second fruit cluster by 16.2%.

Conclusions Foliar spraying of pig blood-derived amino acid-chelated calcium effectively mitigates the oxidative damage induced by salt stress, boosting photosynthetic rate, nutrient uptake, and calcium accumulation in tomato fruits. These results in a significant improvement in tomato yield and fruit quality. Despite its superior salt-resistance effect to that of calcium chloride, the tomato yields still fall short to those achieved in non-stress soil conditions, further research is required to enhance its efficacy.