Effect of Nanohydroxyapatite in Lowland Rice and Simulation of Phosphorus Transport using Hydrus-1D

Excessive phosphorus (P) application through conventional fertilizers to maintain crop yield has increased P pollution and created environmental concerns with serious implications on surface and ground waters. To improve the P nutrient uptake and minimized the undesirable impacts of conventional P fertilizer, nanoparticle such as hydroxyapatite nanoparticle (HANP) was synthesized using the phosphoric acid-treated calcinated chicken eggshells in a planetary ball mill. The synthesized HANP was used as a P nutrient source for lowland rice and the effects on rice agronomical parameters (plant height, tiller count, biomass and yield), P transport and leaching in rice soil with the application of HANP as a P source were studied alongside conventional fertilizer (SSP) and control experiments (CNT) for three seasons (Rabi 2018-19, Kharif and Rabi 2019-20) using field columns. Then the water flow and P transport were simulated with the help of the Hydrus-1D model. The nanoparticles size HANP resulted after 10 hours of milling with a milling speed of 500 rpm and they were observed to be mostly oval in shape with an average particle size of 105 nm. The field column studies indicated an improved plant height, tiller count and yield with HANP and SSP treatment as compared to CNT treatment. No significant difference was observed between HANP and SSP treatment. A significant difference in ortho-P concentration between HANP and SSP treatment was observed in both ponding water and leachate water with higher ortho-P concentrations in SSP as compared to HANP treatment. The simulation results indicated that the Hydrus-1D model successfully simulated the bottom flux and the ortho-P concentration in the leachate very well with a good coefficient of determination (R²), Nash–Sutcliffe efficiency (NSE) and root mean square error (RMSE) values. The value of distribution coefficient K_d was found to be higher in the case of HANP as compared to SSP treatment indicating that more adsorption of P to soil particles occurs in HANP treatment. While the longitudinal dispersivity and the diffusion or precipitation rate constant were approximately higher in SSP treatment than in HANP treatments indicating less local variations in the velocity field of ortho-P in the direction of fluid flow, and a lower dissolution rate of HANP treatment as compared to SSP treatment. Thus the potential of HANP for use as P fertilizer can be demonstrated by the ability to sustain the agronomical parameters of rice crops and the reduced leaching rate and slow-releasing property of the material.

Keywords: Hydroxyapatite, phosphorus, rice, nanofertilizer, Hydrus 1D model