The effects of nutrient loading, mixing temperature, time and type of drying method (freeze and oven drying) on the total K content of the potassium-carrageenan fertilizer formulated through ionic crosslinking was evaluated. Direct effect on the total K was observed at varying nutrient loading at nutrient-to-carrier mass ratios 1:2 and 2:1 with no significant effect at varying mixing conditions and drying. Instead, variations are observed on the qualitative properties of potassium-carrageenan such as viscosity due to the thermoreversible properties of kappa-carrageenan. A linear model based on the significant factor was generated to predict the potassium content at the range of nutrient ratio adjusted to 1:2 to 1.5:1 to obtain a center ratio 1:1, with a maximum predicted value of 26.64% w/w. Potassium and carrageenan crosslinking yield an organized helix structure based on SEM micrograph with crystalline structure. Freeze dried fertilizers yield smaller particle sizes about 300nm due to its easily size reducible physical appearance than in oven-drying where film like particles are observed. Further, a decrease in absorbance is observed at increased potassium concentration. Evaluation of release pattern using buffer system shows slower release of nutrient using carrageenan carrier compared to conventional fertilizer at pH sensitive environment.

Nanofertilizer is an emerging technology for exhibiting slow release mechanism of fertilizer application. This slow release mechanism allows increase in nutrient uptake of plants while minimizing environmental pollution; specifically, reducing eutrophication in bodies of water. This study includes parametric and optimization studies for ionic gelation process in the formulation of potassium fertilizer in chitosan polymethacrylic acid (CS-PMAA) carrier, and subsequent characterization of the formulated K fertilizer. A 2k factorial experimnental design was initially implemented to determine significant factors. Results show that polymerization time inversely affects the K content concentration of the K-CS-PMAA fertilizer due to the swelling behavior of chitosan, while K:CS-PMAA ratio directly affects the K content concentration. Upon numerical optimization, the conditions found to maximize K content of the formulated fertilizer are 3000 ppm K+ corresponding to 1.5:1 ratio of the K loading concentration to CS-PMAA carrier for 30 mins polymerization time. The optimum K content of K-CS-PMAA fertilizer is about 34.98% w/w – less than the 44.27% w/w K content of the fertilizer grade, muriate of potash (MOP). The Dynamic Light Scattering (DLS) and Scanning Electron Microscope (SEM) results of 368.1 nm and 75.4 nm, respectively, indicated that K-CS-PMAA is nanosized. The Fourier Transform Infrared Spectroscopy (FT-IR) results proved the presence of CS-PMAA with deviations at 1483.01 and 1405.07 caused by the vibration in the --COO-anion groups of PMAA indicating the attachment of potassium in the nanoparticle. Furthermore, the fertilizer formulated was proved to exhibit slow release behavior with the value of 83.70% K+ release after 48 hours compared to the 99.43% release of MOP.

Fertilizer inefficiencies caused by uncontrolled and rapid nutrient release pose serious environmental threats and economic losses. Adsorption of nutrients in carriers such as clinoptilolite zeolite (CZ) has been proven to be effective in minimizing environmental pollution and improving the duration of nutrient availability in soil. In this study, a complete fertilizer was formulated via the batch impregnation of the combination of nutrient sources, such as urea, calcium hydroxyapatite (CaHAp), and muriate of potash (MoP), in CZ carrier in a 1:1 ratio. Carrier pre-treatment was done by washing CZ with deionized water and ethanol, followed by calcination at 600 °C for 4 hours. The process has 86.92% recovery and increased the cation exchange capacity (CEC) of the carrier from 41.30 cmol(+)/kg soil to 47.7630 cmol(+)/kg soil. The effect of mixture factors (% Urea : % CaHAp : % MoP ratio) and process factors (mixing time and sonication time) on the total nitrogen (N), phosphorus (P), and potassium (K) content was investigated using an Optimal (Combined Mixture) Experimental Design. Statistical analysis showed the direct effect of the mixture factors and the insignificant effect of the process factors on the said responses. The optimum conditions obtained via numerical optimization is as follows: (1) 50 : 23.99 : 14.61 : 11.39 (% PCZ : % Urea : % CaHAp : % MoP) ratio, (2) mixing time of 158.57 minutes, and (3) sonication time of 30 minutes. This resulted to a fertilizer with a total N, P, and K content of 4.65 % 2.76 %, and 5.42 %, respectively. Moreover, it has about 1.96 % bound N, 0.28 % bound P, and 2.93 % bound K due to a successful adsorption process. The adsorption process has a high fertilizer yield of 96.49 %. DLS analysis revealed that the optimized product has an average particle size of 4105.8 nm; thus, it cannot be characterized as a nanofertilizer. Cost analysis showed that the formulated complete fertilizer is priced at Php 465.82 per kilogram, which is more expensive than the 14-14-14 conventional fertilizer due to higher cost of production. However, the possible slow/controlled release property of the NPK-PCZ fertilizer could offset the high price due to longer availability of nutrients in soil. As such, this could mean lower rate of fertilizer application thus allowing to save up in resources and manpower.