Modeling Nitrogen Release from Hydroxyapatite-Urea Nanohybrids for Advanced Foliar Nanofertilizers
摘要
Nitrogen applied to the soil through conventional fertilizers is converted by microorganisms into gaseous forms such as ammonia and nitrous oxide, contributing to greenhouse gas emissions. Enhancing nitrogen use efficiency (NUE) through foliar nitrogen (N) application using nanohybrid fertilizers has emerged as a promising strategy to mitigate N losses to ecosystems. This study aimed to examine the kinetics of in vitro N release from a hydroxyapatite-urea nanohybrid (HA-urea), focusing on the effects of temperature and urease enzymes on the dynamics of N release. The HA-urea were synthesized using calcium hydroxide, phosphoric acid, and urea. Physical and chemical characterizations were performed using X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (ATR-FTIR), scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and dynamic light scattering (DLS). In vitro N release experiments were conducted using a dialysis assay to evaluate the effects of temperature (10 °C and 20 °C) and urease on the release of total N, NH₄⁺-N, and NO₃⁻-N. Nitrogen determination was performed using colorimetric methods and ionic chromatography. Release kinetics were assessed by fitting experimental data using non-linear least squares optimization, to six mathematical models, with the best fit determined based on the Akaike Information Criterion (AIC). To assess treatment differences, one-way ANOVA followed by Tukey’s post hoc test was performed. The study further compared maximum N release and kinetic parameters, including the slopes derived from the Langmuir-type kinetics equation, and segmented model. This approach provides a basic comprehensive assessment of N release kinetics for optimized foliar fertilizer application strategies. Total N release in all treatments followed a power-law behavior, characterized by a rapid initial release phase (0–80 min), followed by a quasi-plateau phase with a near-constant N release rate. Treatments conducted at 20ºC released 85% of total N and 90% of the potentially releasable N (initial N), regardless of the presence of urease, while treatments run at 10ºC released less than 50% of total N. A similar pattern for total N, but with steeper slopes between 30 and 95 min was observed for NH₄+-N release, with urease exhibiting a linear release trend without a plateau when run at 20ºC. Release of NO₃⁻-N was negligible, accounting for less than 0.09% of initial N, and showed distinct patterns from total N and NH₄-N. Higher NO₃−-N release was observed in treatments with urease notwithstanding of the temperature, but the highest release NO₃⁻-N was observed at 20ºC with urease. Model fitting for total N and NH₄+-N release identified the Korsmeyer-Peppas and Sahlin-Peppas models as the best fits (lower AIC). Maximum total N release at 20 °C was higher than at 10 °C. The presence of urease generally increased NH₄+-N release, with the highest release observed at 20 °C. Additionally, the effect of temperature on NO₃⁻-N release was prominent, with treatments at 20 °C showing higher NO₃⁻-N release, although the NO3⁻ concentrations were similar at the end of the experiment at both temperatures with and without urease. The model that provided the best fit for our data was the Korsmeyer-Peppas model. It demonstrates that both temperature and urease are crucial factors influencing N release from HA-urea treatments. These findings could have practical implications for improving foliar targeted N fertilization and NUE in agricultural systems when using nanofertilizers, bypassing interactions occurring in the soil’s biogeochemical cycle, including ammonification produced by soil urease. Due to its small size and greater specific surface area, urea-HA can be used at low doses, which penetrate the leaf cuticle quickly and efficiently before interacting with urease. This reduces the likelihood that urea-HA may undergo physical and chemical transformations before entering the plant, ultimately reducing the greenhouse gas emissions associated with the application of conventional fertilizers.