Diatomite and Fly Ash Enhance Silicon Availability, Nutrient Uptake, and Yield of Sweet Corn in Humid Tropical Sandy Loam

This study evaluated the effects of diatomite (DT) and fly ash (FA) on soil pH, silicon (Si) availability, nutrient partitioning, and sweet corn (Zea mays L. var. saccharata) productivity in sandy loam soil under greenhouse conditions in northeastern Thailand. A 12-week pot experiment was conducted using a completely randomized design with DT (6 and 12 g/pot), DT combined with FA (10 and 20% of DT), silicic acid (SA), and a control. Combined DT + FA treatments increased soil pH by up to 17.8% (6.57 to 7.74) and enhanced water-soluble Si by up to 53.6% (51.35 mg/kg), indicating sustained Si release. Sweet corn yield was improved, with the highest cob fresh and dry weights recorded under DT (12 g/pot) + FA (10%) (~30% increase over control). The highest total fresh biomass was observed under DT (6 g/pot) + FA (10%), suggesting enhanced vegetative growth at lower DT rates. Nutrient uptake increased markedly, particularly for N and Si, with Si accumulation mainly seen in straw. These responses reflect integrated effects of Si availability, pH improvement, and nutrient inputs rather than Si alone. Overall, DT + FA improved soil properties and plant performance; however, results from this short-term pot study should be interpreted cautiously. Long-term field studies are required to assess sustainability and environmental risks.