Tecnologias para o uso eficiente de fertilizantes fosfatados na soja: caracterização, aplicações e perspectivas integradas

Abstract

In tropical soils, phosphorus (P) efficiency in agriculture is often compromised by low nutrient availability, the presence of iron (Fe) and aluminum (Al) oxides, and soil acidity. Consequently, controlled-release fertilizers (CRFs) are viable options to enhance nutrient use efficiency by gradually releasing nutrients, thus reducing losses and improving their availability to plants over time. Furthermore, apart from phosphorus-related issues, these soils frequently exhibit deficiencies in micronutrients such as zinc (Zn), copper (Cu), manganese (Mn), and boron (B). Coupled with the low quantities required by crops, this creates a challenge of uniform distribution. Thus, the primary objective of the first chapter of this study was to investigate the addition of micronutrients as coatings on phosphate fertilizers, thereby creating multinutrient fertilizers. These were subsequently tested in soybean cultivation. Utilizing MAP and an NPS fertilizer coated with Maxxi-Phos®, alongside technologies like Wolftrax®, Microsol®, or MIB Precise®, results showed phosphorus diffusion ranging from 5.58 to 18.88 mm over 336 hours. Micronutrient use efficiency varied with soybean phenological stages, particularly highlighting stage V4. Nutrient exports were as follows: 55.7 kg of P2O5 ha-1, 209.6 g ha-1 of B, 109 g ha-1of Mn, 216.7 g ha-1of Zn, and 64.3 g ha-1of Cu. In the field trial, significant absorption (p ≤ 0.05) of B, Mn, and Zn occurred during stages R1 to R5.1, while for Cu, it occurred between V4 and R1. Micronutrient-coated phosphate fertilizers demonstrated the capacity to replenish exported nutrients, serving as an effective alternative for multinutrient fertilization of soybeans. As for the second chapter, four commercial CRFs (Agrocote® E-Max 10-48-00 and Agrocote® E-Max 09-47-00, Multicote™ Agri 4, and Multicote™ Agri 8) were evaluated for their physical and chemical properties, including P diffusion, nutrient release in water, thermal stability, salinity index, pH, hygroscopicity, and hardness. Results revealed that MAP released the highest amount of P2O5 on the first day, while Agrocote® 10-48-00 exhibited greater diffusion over time. Polymer use in fertilizer coating reduced and delayed the peak salinity index, decreased acidity, and promoted continuous diffusion of phosphate fertilizer. Nitrogen (N) release differed from P2O5 release in fertilizers, with variations over days. The study underscores the significance of nutrient release across all CRF chemical indices, highlighting optimization possibilities by selecting suitable fertilizer and coating materials. These findings provide valuable insights for the more efficient and sustainable use of fertilizers in tropical soils, contributing to enhanced crop yields and reduced environmental impact.