Preparation and characterization of nutrient rich nanoparticles/composites for agricultural applications

Abstract

The work describes a novel strategy for controlled and sustained release of plant nutrients nitrogen (N), phosphorous (P) and potassium (K) into soil. In the study two nano systems, (a) inorganic inner nano-core consisting of macronutrient nanoparticles (b) a natural cellulose based outer core containing micro / nano porous cavities were used in order to obtain slow and sustained release of nutrients. Hydroxyapatite (HA) nanoparticles were synthesized, surface modified using urea and characterized using PXRD, SEM / EDX, AFM, FTIR and TGA / DTA. Urea modified HA nanoparticles dispersion and saturated potassium chloride solution were separately pressurized into the cavities present in Gliricidia sepium, a soft wood stem, under a pressure of 9 bar. N, P and K release behavior ofthe nanofertilizer composition was studied using soil from three elevations in Sri Lanka (pH 4.2, 5.2 and 7) and the release properties were compared with that of a commercial fertilizer composition. The release properties ofthe nanofertilizer show a slow and sustained release. In general, at all pH values, even on day 32, the remaining N to be released in the nanofertilizer was about 20% and there was no more N to be released in the commercial fertilizer. A similar trend shows for K release and at all pH values the remaining K to be released in nanofertilizer after 40 days was about 15% while there was no more K to be released in the commercial fertilizer. The solubility of P of in the nanofertilizer system was higher than the P release of the commercial fertilizer. A model was developed for the solubility of bulk HA / HA nanoparticles. The solubility of HA in terms ofsoluble phosphate (P043') can be expressed by an equation, 3 4 7 10-if vjcw; p0*3"L 5 total 2.503Kfl2+fx0.509Xv7] 8 3 5*e From pH 3 to 4 and pH 4.5 to 6 the decrement of log value of total soluble phosphate concentration per unit pH is 11.8 and 3.03, respectively, when the ionic strength of the soil solution is between 12 to 110 mol kg'1 according to the Ostwald and Freundlich equation, the solubility of phosphate can be increased by reducing the size of HA, that is, by using HA nanoparticles.