USO DE MODELAGEM DE EQUAÇÕES ESTRUTURAIS (MEE), PARA AVALIAR A INFLUÊNCIA DE FERTILIZANTES FOSFATADOS SOBRE A DINÂMICA DAS FRAÇÕES DE FÓSFORO NO SOLO

Abstract

Phosphorus (P) is an essential element for plant development. However, in tropical soils, its availability to crops is reduced due to intense adsorption processes by the iron and aluminum oxides present in these soils. Understanding the P dynamics in soils and how different sources can alter this dynamic is crucial for increasing fertilizer use efficiency. Thus, this study aimed to evaluate the use of structural equation modeling (SEM) in understanding soil P dynamics and how different sources, both soluble and low-solubility, can alter this dynamic. A database from an experiment testing triple superphosphate (TSP) and Arad reactive phosphate (ARP) on a typical dystrophic Haplic Cambisol (CXbd) and a typical dystrophic Red Latosol (LVd) was used. For P fractions characterizations, the sequential Hedley fractionation method was employed. The methodology included structural equation modeling (SEM) to evaluate the interactions between P Pools. The soil P Pools were latent constructs estimated based on the soil P fractions as follows: Inorganic Pool = Labile-Pi + Fe+Al-Pi + Non-Labile-Pi; Organic Pool = Labile-Po + Moderately Labile-Po + Non-Labile-Po; Mineral Pool = Ca-Pi; Occluded Pool = Occluded-Pi; and Available Pool = Solution-Pi. In the model hypothesis test, the Available Pool is a function of the other P Pools: Available Pool = Inorganic Pool + Organic Pool + Mineral Pool + Occluded Pool. Tests were conducted with the databases using the full model. Full models with low fit and absence of component significance were respecified based on correlation tests and/or Bartlett's sphericity test and the Kaiser-Meyer-Olkin (KMO) index. The results showed that in the Cambisol with ARP, the moderately labile organic fraction (Moderately Labile-Po) is the main P source for the available pool. In the TSP treatment, phosphorus is rapidly solubilized but also exhibits higher fixation. In the Latosol, ARP maintains P in non-labile forms, promoting gradual release, while TSP provides rapid availability but with more intense immobilization. Thus, understanding the relationships between phosphorus fractions and phosphate fertilization in tropical soils through SEM becomes important to assist in the choice of P source and appropriate management to increase the availability of this nutrient to plants, mitigating environmental impacts and improving the utilization of applied inputs.

Keywords: P compartments; Multivariate analysis; Tropical soils; Arad reactive phosphate; Triple superphosphate.