MANEJO DE ADUBAÇÃO FOSFATADA COM FERTILIZANTES DE EFICIÊNCIA AUMENTADA

Abstract

Phosphorus (P) is vital for agricultural productivity and global food security. Although global reserves of phosphate rock remain available, their geographically concentrated distribution requires more efficient nutrient use and reduced external dependence. In Brazilian tropical soils, high acidity and abundance of iron and aluminum oxides intensify P fixation and lower its agronomic efficiency, particularly when highly soluble sources are used. Smart phosphorus management strategies, guided by the 4R principles (right source, right rate, right place, and right time), have gained attention for combining efficiency, sustainability, and circular-economy approaches. In this context, organic and polymeric fertilizer additives represent promising alternatives to modulate P release and minimize losses. To evaluate these effects, greenhouse incubation experiments, structural equation modeling (SEM), and field trials with soybean and maize were carried out to assess P dynamics and utilization under contrasting soils and management conditions. Three soils were tested: Acriferric Red-Yellow Latosol (LVAwf), Typic Orthic Quartzarenic Neosol (RQo), and Typic Eutrophic Red Nitosol (NVe). Each soil followed a 2 × 3 + 1 factorial design with two P sources (MAP and ST), three additive conditions (none, KimcoatBioHP®, and IFCoat), and one control, with soil samples collected at 30, 90, 180, 270, and 360 days. Phosphorus fractions were determined by the Hedley sequential fractionation method (Hedley et al., 1982), in which soluble P was extracted using ammonium chloride (NH₄Cl). Results were integrated using multivariate analyses and SEM, treating measured fractions as observed variables associated with latent constructs (Organic, Inorganic, Mineral, Occluded, and Available Pools), allowing the identification of the main determinants of P availability in each soil. Phosphorus dynamics varied across soils, sources, and additives. In the RQo, a sandy soil with low cation-exchange capacity, MAP combined with additives increased soluble Pi at 30 days, but P was rapidly converted to non-labile (Pi-NL) and occluded (Pi-occ) forms, reducing its persistence. From 90 days onward, ST without additives sustained higher availability, indicating that slow-release sources and split applications are more suitable for this soil. In the LVAwf, rich in Fe and Al oxides, strong initial immobilization occurred, with occluded P acting as a secondary reserve. MAP + IFCoat reduced precipitation into insoluble forms and maintained higher soluble and labile Pi between 90 and 180 days, while ST showed slower dissolution and greater Ca-phosphate retention. In the NVe, with higher clay and organic-matter content, microbial cycling influenced P transformation, increasing microbial (Po-mic) and moderately labile organic (Po-ML) fractions, which acted as transient reservoirs. SEM results confirmed distinct controlling pools: the inorganic pool in RQo, occluded pool in LVAwf, and organic pool in NVe, showing that soil mineralogy and biology govern P maintenance in solution. Field experiments evaluated source and additive effects on P availability and crop performance. Soybean was grown under a completely randomized design with MAP applied in rows or broadcast, combined with six PhytohumusBio® doses (0–7.5 kg Mg⁻¹). Maize was grown in randomized blocks (2 × 4 + 1) with two sources (MAP and MAP + KimcoatBioHP®), four P rates (70, 85, 100, and 115 % of the recommendation), and a control. In soybean, PhytohumusBio® increased grain yield by 550 kg ha⁻¹ and P agronomic efficiency by 73.2 kg grain kg⁻¹ additive compared with MAP alone, especially under row application. For maize, MAP + KimcoatBioHP® reduced early growth but did not affect final yield, due to climatic stress during the season. Overall, the results demonstrate that humic and polymeric additives associated with phosphate fertilizers are promising tools to improve P use efficiency. Their effectiveness, however, depends on soil mineralogy, biological activity, and management strategy. The smart phosphorus management concept, integrating the right soil, source, and additive, proved essential to maintain P in labile forms, reduce losses, and support sustainable agriculture in tropical environments.