Fig. 3. Regression between observed and estimated carob-tree yield obtained by the six-parameter model presented in Table 4. Standard errors of the means are shown for both variables. Fertilization regimes used in the validation trial are: N (solid circles); K (open triangles); N plus K (solid squares); and unfertilized control (open circles). Upper and lower limits for the observed yield are represented by two dashed lines. Both lines were obtained by regression analysis.