Fig. 3. Percentage of added KNO3 fertilizer used by plants as revealed by 15N incorporation. F1 and F2 denote the fertilizer levels (10 or 20 mg N pot1). Different letters indicate significant differences at a ¼ 0.05. Soil type had no significant influence,squares give mean values of both fertilizer levels. Data are given with respective standard deviations. HTC: hydrochar, PC: pyrochar.