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Background Polyhalite fertilizer application is an effective way to alleviate a shortage of potassium. This study explored the effects of polyhalite fertilizer application as a total or partial replacement for conventional potassium fertilizer to improve peanut growth and soil quality. Results The index of peanut yield and its economic benefits, the content and distribution of mineral nutrients in different organs, soil chemical properties, and rhizosphere microbial diversity in response to the treatments were examined. The results show that the M4P6T treatment (60% polyhalite fertilizer replacing potassium chloride as the base fertilizer, and 40% potassium chloride fertilizer applied as a topdressing) increased profit by 7.2% without affecting the yield. The M4P6T treatment significantly improved the accumulation and distribution of potassium, calcium and magnesium in the kernels compared with the M10B treatment (no polyhalite fertilizer; potassium chloride fertilizer only as the base fertilizer). Soil treated with polyhalite fertilizer had higher alpha-diversity values and greater relative abundance of microbes at the phylum and genus levels. Conclusions Partial substitution of polyhalite for potassium chloride improved soil quality and peanut growth more than did single applications of polyhalite and potassium chloride. Graphical Abstract

The prevalent use of foliar calcium fertilizers in peanut production is inorganic, but calcium absorbed from the foliar has poor availability. Sorbitol-chelated calcium is a novel organic foliar calcium fertilizer that has rarely been studied for application in peanut production. To explore whether calcium absorption and peanut yields can be affected by foliar application of sorbitol-chelated calcium, this study conducted two field experiments using Virginia peanut (Huayu-22) in 2020 and 2021. The five spray treatments included: deionized water (CK), sorbitol (Sor), calcium nitrate (CaN), a mixture of sorbitol and calcium nitrate (SN), and sorbitol-chelated calcium (SC). The yield of peanuts treated with sorbitol-chelated calcium was increased by 12.31-16.63%, 10.22-11.83%, 6.31-9.69%, and 4.18-6.99% compared to the CK, Sor, CaN, and SN treatments, respectively. Sorbitol-chelated calcium had the lowest contact angle due to the wetting effect of sorbitol, which promoted calcium absorption by leaves. Sorbitol-chelated calcium improved the leaf calcium concentration by 13.12-19.32% and kernel calcium concentration by 6.49-8.15% compared to the CK treatment. Foliar fertilization increased the calcium concentration of each subcellular fraction of leaves and changed the distribution of calcium in mesophyll cells. This change was directly observed by transmission electron microscopy. Additionally, spraying sorbitol alone obtained similar effects to spraying calcium nitrate alone, indicating that the benefits of sorbitol itself were not negligible. The results of the principal component and correlation analysis showed that the increase in calcium concentrations and the change in calcium distribution improved the pod traits of the peanut, thus affecting the peanut yield. The above results showed that from the perspective of calcium absorption and distribution, sorbitol-chelated calcium is a more effective foliar calcium fortifier for peanuts and effectively improves peanut yields.