Balanced Phosphorus Fractionation and Organic Carbon Accumulation With Organomineral Fertilizers in Weathered Tropical Soils

Tropical soils are, for the most part, highly weathered, which results in low natural fertility and high phosphorus (P) fixation, requiring the application of this nutrient to meet crop demands. In this context, organomineral fertilizers, unlike mineral fertilizers, provide gradual release of P and an organic matrix capable of promoting additional benefits to the soil. The objective of this study was to evaluate the influence of different types of fertilization (control, mineral and organomineral) and different doses on soil chemical properties, organic carbon and the distribution of P forms, aiming to understand the dynamics of P in the soil. The study was conducted in Maripá, PR, Brazil, in a randomized block design, with ten treatments: control without fertilization (CTR) and nine combinations of three doses (50%, 70% and 100% of the recommendation) of a mineral fertilizer (MAP) and two organomineral fertilizers (SPGAN and ORGANPLUS). Disturbed soil samples were collected at depths of 0–5, 5–10 and 10–20 cm. After collection, the samples were air‐dried, crushed, and sieved to obtain air‐dried fine earth (ADFE). Chemical properties of the soil, as well as the total organic carbon (TOC) content, were evaluated using the ADFE. P contents and proportions were also determined by sequential extraction: soluble (Psol), available (PM3), inorganic (PiOH), organic (PoOH), calcium‐bound (PHCl) and occluded (Pocc). The data were evaluated for normality and homogeneity of variances. For statistical analyses, parametric Tukey's mean comparison test (5%) was used, while for non‐parametric analyses, Kruskal–Wallis and Dunn tests (5%) were applied. In addition, Spearman correlation, principal component, and redundancy analysis (RDA) analyses were performed. Chemical properties of the soil and TOC were influenced by the fertilizer sources and showed higher values at 0–5 cm depth, with a reduction in subsurface. For MAP, ORGANPLUS and SPGAN fertilizers, higher values were found in comparison to CTR, with MAP showing the lowest TOC supply. P fractionation revealed that organomineral fertilizers, especially ORGANPLUS, promoted a better balance between labile, organic and stable fractions, while MAP, due to the form of P release, may favour greater fixation in the soil. The RDA results indicated that P dynamics are controlled by the interaction between soil chemical attributes, TOC, and management factors, especially fertilizer source and soil depth, highlighting the role of SOM in regulating P lability. Thus, organomineral fertilizers may result in greater efficiency in P use and greater sustainability in the medium and long term.