Objectives In China, natural rubber production is plagued by irrational fertilization practices and low latex quality. The effects of various fertilization methods and fertilizer combinations on soil nutrients, rubber yield and quality were studied to provide technical support for the green and efficient production of natural rubber.

Methods A field experiment was conducted in 2023 at the Experimental Farm of the Chinese Academy of Tropical Agricultural Sciences in Danzhou City, Hainan Province. Twelve treatments were designed, on the base of conventional NPK fertilization (T). The 12 treatments were composed of single and combined application of zinc-molybdenum fertilizer tapping on the rubber tapping panel (Z), silicon-boron fertilizer applied in caves (S), water-soluble organic fertilizer sprayed on the soil belt between tree rows (C), and Fe-Mn oxidizing bacteria inoculant sprayed on inter row soil (B). At the end of the experiment, soil samples were collected to determine the basic physicochemical properties of the soil in inter-row soil belt and fertilization caves. The latex yield and quality of raw rubber were investigated. The entropy weight-TOPSIS method was used to comprehensively evaluate and optimize the effects of various fertilization measures.

Results Compared with T, all the 8 treatments containing C significantly increased soil pH and available K content, increased soil organic matter content by 19.9% to 34.4%. Except for the CBS treatment, other 7 C-containing treatments significantly increased dry rubber yield by 25.5% to 49.3%. Except for the single C treatment, the other 7 C-containing treatments significantly reduced free Ca content in latex by 20.0% to 33.0%. Additionally, the treatment CZS significantly increased thiol and inorganic P content in latex by 10.2% and 22.5%, respectively, increased the weight-average molecular weight of natural rubber (reaching 180.28×10⁴ g/mol) and reduced the width coefficient of molecular weight distribution. The entropy weight-TOPSIS analysis revealed that the CZS treatment had the best overall effect on improving latex yield and raw rubber quality, followed by treatment CS, C, and CBZS in turn.

Conclusions Cave application of silicon-boron fertilizer increased the soil pH, while water-soluble organic fertilizer increased the soil pH, available K, and organic matter content. On the basis of base fertilization with NPK compound fertilizer, the combined application of water-soluble organic fertilizer, zinc-molybdenum fertilizer, and silicon-boron fertilizer (CZS treatment) further significantly increased dry rubber yield, reduced free calcium content in latex and the width coefficient of rubber molecular weight distribution, significantly increased thiol and inorganic phosphorus content, improved the number-average molecular weight and weight-average molecular weight of rubber, and resulted in excellent initial plasticity value, plasticity retention rate, and Mooney viscosity of natural rubber.