Optimizing Potato Yield and Maintaining Soil Fertility in Chitwan, Nepal: Can Bioinoculants Offset the Reduction in Mineral Fertilizers?

Phosphorus and potassium are progressively declining in agricultural soils, and a large share of applied nutrients is fixed in the soil, making them yield‐limiting factors. Plant growth‐promoting microorganisms enhance the availability and uptake of essential nutrients, thereby reducing the application of chemical fertilizers. Considering these facts, a field experiment was conducted at Rampur, Chitwan, to evaluate the effects of integrating biofertilizers, chemical fertilizers, and farmyard manure (FYM) on potato (cv. Janak Dev), with the hypothesis that biofertilizers can compensate for a fraction of chemical fertilizer without a significant reduction in yield. The experiment was arranged in a split‐plot design with FYM application (with and without) as the main plot factor and combinations of chemical and biofertilizers as the subplot factor, with three replications. Results showed that the individual effect of FYM was not significant for the measured variables. Plant height and leaf area index (LAI) were not significantly different between the recommended dose of chemical fertilizers (RDFs) and the application of biofertilizers combined with a 25% low RDF. Similarly, tuber yield and financial indicators did not differ statistically between RDF and the combination of reduced RDF with phosphate‐solubilizing bacteria (PSB) or arbuscular mycorrhizal fungi (AMF). In contrast, potassium‐solubilizing bacteria (KSB) combined with reduced RDF resulted in a significantly lower yield than RDF alone. FYM alone had no significant effect on potato growth, yield, or soil chemical properties based on split‐plot analysis of variance (ANOVA), although an exploratory paired t ‐test comparing the corresponding with‐ and without‐FYM observations showed a significant difference in yield (mean difference = 1.48 t ha ⁻¹ ; p = 0.037). Similarly, FYM‐treated plots showed numerically higher soil organic matter content, total nitrogen, and available potassium by 15.31%, 16%, and 8.25%, respectively, compared to plots without FYM. Likewise, with the FYM application, PSB and KSB under reduced RDF were more responsive in increasing crop yield. Overall, the application of biofertilizers in combination with a reduced chemical fertilizer dose resulted in growth and yields comparable to those achieved with the full chemical fertilizer dose. Additionally, integrating FYM with PSB under reduced RDF increased economic returns.