Fig. 2. Predicted tissue Zn concentration of rice at the midtillering stage as affected by Zn fertilizer source and application rate during 2000 at the Pine Tree Branch Station (PTBS) and Rice Research Extension Center (RREC). For reference, the dashed horizontal line (20 mg Zn kg^–1) represents the critical Zn concentration. Mean Zn concentrations are shown as for the unfertilized control (0 kg Zn ha^–1), • for zinc sulfate 31% Zn (ZnSul31), for zinc lignosulfonate 10% Zn (ZnLig10), for zinc oxysulfate 20% Zn (ZnOxy20), and for zinc oxysulfate 36% Zn (ZnOxy36). For the PTBS, standard errors were 1.5 for intercept and 0.08 for linear coefficient. For the RREC, standard errors were 1.6 for intercept and 0.14 for linear coefficient.