The deficiency of available silicon (Si) incurred by year-round agricultural and horticultural practices highlights the significance of Si fertilization for soil replenishment. This study focuses on a novel and economical route for the synthesis of Si fertilizer via the calcination method using talc and calcium carbonate (CaCO₃) as starting materials. The molar ratio of talc to CaCO₃ of 1:2.0, calcination temperature of 1150 °C and calcination time of 120 min were identified as the optimal conditions to maximize the available Si content of the prepared Si fertilizer. X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR) characterizations elucidate the principles of the calcination temperature-dependent microstructure evolution of Si fertilizers, and the akermanite Ca₂Mg(Si₂O₇) and merwinite Ca₃Mg(SiO₄)₂ were identified as the primary silicates products. The results of release and solubility experiments suggest the content of available metallic element and slow-release property of the Si fertilizer obtained at the optimum preparation condition (Si-OPC). The surface morphology and properties of Si-OPC were illuminated by the results of scanning electron microscope (SEM), surface area and nitrogen adsorption analysis. The acceleration action of CaCO₃ in the decomposition process of talc was demonstrated by the thermogravimetry-differential scanning calorimetry (TG-DSC) test. The pot experiment corroborates that 5 g kg⁻¹ soil Si-OPC application sufficed to facilitate the pakchoi growth by providing nutrient elements. This evidence indicates the prepared Si fertilizer as a promising candidate for Si-deficient soil replenishment.

Irrigation purposes within Bantul area which is located on Yogyakarta Volcanic Groundwater Basin, 47 existing data points were used complementary with the results of 30 groundwater samples analysis which were collected from dug and tub wells in various locations of study area. ECw, TDS, pH and major cations: Na+, Ca2+, Mg2+, K+,and anions: Cl􀀀, HCO􀀀 3 , SO2􀀀 4 , NO􀀀 3 were analyzed as evaluation index. The relative tendency of ion in epm shows Ca2+>K+>Na+>Mg2+ and HCO􀀀 3 >Cl􀀀>SO2􀀀 4 . Variations in groundwater composition by using Mg/Ca vs. Na/Ca molar ratio indicates that the groundwater is close to silicate rock with influence of clastic carbonate rock. Higher salinity approach to the west of the Bantul indicates that groundwater quality is controlled by clastic carbonate rock and expose limestone of Sentolo hills. Groundwater samples fall under class I suggested that groundwater is good and suitable for irrigation based on Doneen’s classification of permeability index and 78.37% is in excellent category by Wilcox classification on N%. According to the SAR values plotted in the USSL diagram, the majority of the groundwater samples belong to C2-S1 and C2-S2 class, indicating medium salinity and low sodium water which can be used for irrigation with little danger. The suitability of groundwater quality for agriculture is determined by thematic maps produced from ArcGIS Spatial Analyst based on FAO guideline. Salinity is the significant problem that has slight to moderate restriction effect on crops productivities in this area. The ECw map indicates that good groundwater quality for crops is at the middle to the east of study area close to Opak River, while at the western irrigation water is affected but yielding no reduction on rice productivity. However, it has slight to moderate restriction on sensitive crops indicated in thematic map of crops land with different yield potential. The agricultural land in which has yield potential of 100%, 90% and 75% is about 2727.90 ha (38.56%), 735.49 ha (10.39%) and 208.98 ha (2.95%) of the study area respectively. Key words: Irrigation groundwater quality, total dissolved solids (TDS), electrical conductivity (EC), evaluation index, ArcGIS Spatial Analyst, FAO guideline, yield potential.