Evaluation of Natural Rock Powder as a Potassium Source for Onion (Allium cepa L.) Cultivation

This study was conducted to evaluate the potential of natural rock powder (NRP), derived from potassium (K) feldspar, as an eco-friendly K fertilizer for onion (Allium cepa L.) cultivation under vinyl mulching conditions.The experimental design included a mineral fertilizer control and various NRP treatments (standard rate, double rate, micro-particles, and foliar application).The results showed no significant differences in onion fresh weight or bulb diameter across all treatments, suggesting that NRP can support basic crop growth.However, the K content in plant tissues was lower in NRP-treated plots compared to the control, with significant reductions observed in the NRP-2 and NRP-MP groups.This lower K uptake is attributed to the low solubility of NRP and its tendency to remain on the mulch surface during top-dressing, which limits nutrient penetration into the soil.Lab-scale elution tests confirmed that the control released approximately twice as much cumulative K as the NRP treatments, although Si release was comparable due to the mineral composition of the raw material.While NRP shows promise as a sustainable K source, enhancing its solubility through formulation improvements or specialized application methods is essential to optimize its efficacy in plastic-mulched cropping systems.