An exploratory analysis of phosphorus transformations in tropical soils using structural equation modeling

In the tropics, highly weathered soils with high phosphorus (P) fixation capacities predominate, reducing the P availability to plants. For this reason, understanding the cycle of P in the soil is important to develop management strategies that increase P availability to plants, especially in low-input production systems. The aim of this study was to apply structural equation modeling with latent variables, at an exploratory level, to test hypothetical models of the P cycle using data from the Hedley extraction method. Specifically, we evaluated interactions between the pools of P, and identified which pools act as a sink or source of P in unfertilized soils. The models of the P cycle for the tested soil were able to distinguish between the direct and indirect effects of labile and stable P on the available P pool. This approach led to a proposed distinction of functional P pools in the soil, and identifying the processes of P transformation in the soil between the pools based on a source-sink relationship. Based on these analyses, the organic pool consists of the bicarbonate organic phosphate (Po), hydroxide Po, and sonic Po fractions. The bicarbonate inorganic phosphate (Pi) and hydroxide Pi fractions formed the inorganic pool. The hydrochloride (HCl) P-hot and residual P fractions formed the occluded pool, the HCl Pi fraction formed the primary mineral pool, and the resin Pi fraction constituted the most available P pool. Organic P pool was the major source to the available P pool.