Nanometric phosphates dispersed in urea on phosphorus agronomic efficiency in oxidic soil

Author(s)

Heitor Pontes Gestal Reis

• Document type: Doctoral Thesis
• Press: Botucatu. 2021-08-31.
• Institution: Universidade Estadual Paulista (Unesp). Faculdade de Ciências Agronômicas. Botucatu
• Defense date: 2021-07-12
• Advisor: Dirceu Maximino Fernandes

Abstract

Phosphorus (P) is an important macronutrient responsible for the growth and production of agricultural crops. Developing efficient fertilization practices has become increasingly important due to the growing global food demand. About 80-90% of P applied as a fertilizer is lost to the environment or chemically bound to the soil, therefore not available to plants. Nanoparticulate fertilizers have the potential to improve P efficiency, based on the hypothesis that nanometer-sized particles have greater mobility and availability in the soil. However, a challenge to be overcome is strategies development to maintain the phosphate particles on a nanometric scale and prevent their re-agglomeration. Recent studies have shown that fertilizing urea has potential as a matrix for dispersing mineral phosphates, avoiding particles re-agglomeration, increasing solubility and changing P dynamics in the soil. Therefore, the central purpose of this work was to process and characterize nanocomposites based on hydroxyapatite (HAP) (used as a model mineral phosphates source), Bayóvar (BAY) and triple superphosphate (STP) dispersion in urea matrix, and evaluate the agronomic aspects related to P dynamics in the soil and this nutrient supply to the plant, as well as understanding the synergism and the interaction between urea and phosphate particles. New fertilizer preparation was based on the extrusion process, from HAP, BAY and STP fractions, ground to nanometric ranges and dispersed in urea and starch matrix by this method. After the synthesis, the nanocomposites were characterized, followed by agronomic efficiency experiments. The first study was carried out with the objective to understanding the release rate and the phosphate ion release kinetics in soil. For that, bench studies were carried out to evaluate release rate to fertilizers over a week. In Petri dishes, the granules of each fertilizer were inserted in dish center and the P diffusion zone was evaluated by the non-destructive method by marking it on filter papers, in order to obtain a P path timeline. At the end, P levels and pH were determined at different distances from dishes center. In a greenhouse, an experiment was carried out in pots with the objective to evaluating P dynamics, using the sequential extraction method, as well as evaluating the roots growth using the WinRhizo software, in addition to verifying the capacity of these materials to supply Panicum maximum cv. BRS ‘Zuri’ nutritional demand, since four cuts were made at the time the plants reached the cutting height. Finally, also in a greenhouse, another experiment was carried out using Plant Growth Containers (PGCs) in order to assess P mobility and its ability to reach the plant roots. To this study, the materials HAP, HAP 2:1, STP and STP 2:1 were selected, being applied to the PGCs bottom at a 5.0 cm depth in two systems types, with plant and without plant. The results reveal that the dispersion matrix was effective in maintaining the phosphate particles on a nanoscale, avoiding the re-agglomeration process and optimizing the phosphate ion release process over time. An increase in soil pH was also observed in the region of nanocomposite granules application, with a consequent increase in available P content. The plants results reveal a greater P use efficiency in the composites originated from the STP in relation to the original source. It was also clear this technology great potential when we observed the PGCs results, being the P resin levels in the soil fertilized with STP 2: 1 revealed higher P amounts available to the plants in relation to the conventional STP. (AU)

• FAPESP's process: 18/01444-3 - Nanometric phosphates dispersed in urea on the agronomic efficiency of phosphorus in oxidic soil
• Grantee: Heitor Pontes Gestal Reis
• Support Opportunities: Scholarships in Brazil - Doctorate