The Nitrate-First, Ammonium-Later Strategy in Potato: Implications of Nitrogen Timing, Form, and Soil Transformation

Potato nitrogen (N) demand varies with developmental stage rather than remaining uniformly high throughout the season. This review re-examines the “nitrate-first, ammonium-later” strategy by separating total N amount, N-supply timing, N form, and soil N transformation. Current evidence suggests that nitrate is better aligned with pre-tuber initiation because it supports stolon development and tuber set under non-excessive N supply, whereas ammonium-containing nutrition may benefit tuber bulking only when NH4+ persists in the root zone and soil chemical constraints are controlled. Field responses attributed to N form are often shaped by crop N status, genotype × environment × management interactions, nitrification–denitrification dynamics, water regime, soil texture, fertilizer placement, and cultivar. We therefore interpret the strategy as a conditional, stage-oriented framework rather than a universal fertilizer prescription. Integrating NNI-/CNDC-based diagnosis, root-zone monitoring, enhanced-efficiency fertilizers, and soil-process evidence can improve synchronization between N supply and potato demand, supporting yield formation, N-use efficiency, and reduced environmental risk.