NPK是指任何肥料或营养液中的三种主要大量营养素：氮（N）、磷（P）和钾（K）。营养液瓶子上印制的NPK比例（例如，3-1-2）表示每种元素的重量百分比。氮促进叶片的营养生长，磷支持根系发育和开花，钾调节水分吸收、抗病性和植物的整体活力。
关键事实
- N (Nitrogen): essential for chlorophyll, proteins, and vegetative leaf growth
- P (Phosphorus): drives root development, flowering, and energy transfer (ATP)
- K (Potassium): regulates stomata, water uptake, enzyme activation, and disease resistance
- Ratio 3-1-2 is a common vegetative baseline; flowering stages often shift to lower N, higher P/K
- Deficiency symptoms are element-specific: yellow older leaves (N), purple tints (P), brown leaf edges (K)
- Hydroponic nutrient solutions must supply all three in precise ratios — soil buffers these naturally