Multi-site evaluation of phosphorus fertilization with bio-inputs in sugarcane: Yield and soil P fractions

Background Phosphorus (P) deficiencies in highly weathered tropical soils limits sugarcane productivity, and the agronomic value of bio-inputs and phosphorus reapplication remain uncertain. We evaluated whether integrating bio-inputs with phosphorus fertilization increases yield and modifies soil phosphorus pools across contrasting environments. Methods Field trials were conducted at six commercial sites in South-Central Brazil over two crop cycles. We compared P applied in the planting furrow alone or combined with a biological conditioner or phosphate-solubilizing bacteria; in the first ratoon, P was either reapplied or omitted while maintaining the same bio-input scheme. Stalk yield was measured in both cycles, and sugar yield was derived from technological analyses. After each harvest, soils were sampled and a rapid fractionation quantified labile, moderately labile, occluded, organic, and total P for selected fertilized treatments. Multivariate patterns were summarized with principal component analysis (PCA). Associations between stalk yield and soil P fractions were evaluated using Spearman correlation. Results P at planting consistently increased stalk yield relative to the unfertilized control across sites, with an average gain of approximately 9 Mg ha −1 in plant cane. In the first ratoon, yields were largely sustained by residual P from planting and the cross-site mean effect of reapplication was small and not significant, although clear gains occurred at some locations. Responses to bio-inputs were modest and site dependent: the biological conditioner improved yield at a subset of sites, whereas phosphate-solubilizing products rarely exceeded fertilization alone. Within fertilized treatments, soil P fractionation showed that bio-inputs increased labile P in some site–cycles (direction and magnitude varied by product and cycle) and increased moderately labile P in plant cane, relative to fertilization alone. Shifts among P pools varied by site and cycle and were not consistently associated with yield. PCA indicated that site properties dominated responses, with one clay-rich, high-phosphorus site clustering separately and aligning with higher productivity together with larger moderately labile and total pools. Conclusions and implications P applied at planting was the primary driver of sugarcane yield gains across our multi-site; while additional gains from first-ratoon reapplication or from bio-inputs were small and depended on local conditions. Bio-inputs may offer medium to long term benefits, since they increased the moderately labile soil P fraction at some sites, although this prospect remains uncertain and requires validation under low P supply. Overall, prioritizing P at planting while using site-specific diagnostics to decide on reapplication and to test bio-inputs is the most defensible strategy. These findings support site-specific diagnostics to refine rates, avoid unnecessary inputs, and sustain productivity while stewarding finite P resources.