Nitrogen Fertilization Temporarily Enhances Phosphatase Activity in a High‐P Loamy Sand

Background Efficient plant utilization of soil phosphorus (P) is essential to reduce dependence on mineral P fertilizers in intensive agriculture. Input of mineral nitrogen (N) fertilizers and its chemical form may influence the activity of P mineralizing enzymes, but how this interaction operates under field conditions in a soil with high P status remains poorly understood. Aims This study investigated how different mineral N fertilizer forms influence soil pH and phosphomonoesterase activity during early maize growth, using these parameters as proxies for potential mineralization of organic soil P. Methods A one‐season lysimeter study was conducted with maize ( Zea mays L.) grown on a loamy sand soil with high Olsen‐P content. Nitrogen was applied at a rate of 180 kg N ha −1 as either nitrate‐N or ammonium‐N. A treatment without N was included as a reference. Soil pH and phosphomonoesterase activity were measured in bulk and rhizosphere soil at leaf stages V4, V5 and V6. At silage maturity, dry matter yield and P uptake were determined. Results Nitrogen fertilization increased maize yield by 68%, with similar yields observed for both N forms (25.5–26.0 Mg DM ha −1 ). Rhizosphere pH was consistently higher than bulk soil pH across treatments. At V4, phosphomonoesterase activity was higher in the rhizosphere than in bulk soil in N‐fertilized treatments. Conclusion Nitrogen fertilization momentarily stimulated rhizosphere phosphomonoesterase activity at an early growth stage, indicating altered conditions associated with organic P mineralization. Direct measurements of soil P pools are required to determine whether these changes translate into increased P availability under field conditions.