Paper Title
Slow Release Nitrogen Fertilizer Based on Chicken Eggshell Waste and Hydroxyapatite for Potential Agricultural Applications

Abstract
Crops cannot absorb the use of urea as much as 50-70% in soil due to loss of nutrients. Nutrient loss can be overcome by improving the physical and chemical properties of fertilizers through changes in nutrient solubility systems, fertilizer shapes, and sizes. Slow release of urea is urea fertilizer which can control the release of nutrients for a long time and according to the needs of crops. In this study, Slow release urea was made by modifying of urea with the hydroxyapatite and calcium matrix from the waste of chicken eggshell. Hydroxyapatite has a barrier to nutrient release while silica increases the strength and properties of the carrier as a nutrient carrier. The matrix added to urea is synthesized from natural material waste which is environmentally friendly. The manufacturing stages are the destruction of eggshells into calcium nanoparticles, synthesis of nano-calcium from eggshell, Hydroxyapatite synthesis by the precipitation method, synthesis of Urea-hydroxyapatite, synthesis of urea-nano-calcium. Modification of urea was characterized using XRD, TEM and FTIR and testing of N levels and release test for 15 days using the Kjeldahl method. The results of urea-hydroxyapatite and urea-nano calcium have succeeded in forming nanocomposites and have a size of less than 70 nm for diameter and a maximum of 200 nm for particle length. The morphology resembles a spherical for urea-nano-calcium and rod for Urea-hydroxyapatite. The functional groups identified are functional groups N-H, N-C-N, C = O, C-H belonging to urea, carbonate groups CO32- and O-P-O for hydroxyapatite and nano-calcium. The results of the release test showed that the release of nutrients from the nitrogen was slow to release from urea. The content of nitrogen dissolved in water is 0.358% for urea, 0.26% for urea-hydroxyapatite and 0.24% for urea-nano calcium. This application can be used for crops so that it can reduce nitrogen loss by 32%. Keywords - Urea, Slow Release Fertilizer, Hydroxyapatite, nano-calcium, eggshell.