A new concept of Effective Nutrient Soil Areas (ENSA) was put forward and studied with the regression method. Through conducting experiments with corn and sugar beet, a model of the relationship between ENSA and yield of an individual crop was established. By using the model, an optimal ENSA of corn was worked out as 0.335 m² (57.9 cm×57.9 cm) and that of sugar beet as 0.358 m² (53.4 cm×67 cm). Therefore, for corn and sugar beet the ridge planting method of 67~70 cm in spacing, which is applied widely in the current production, is wasting soil resources, because the plant has a space larger than the ENSA of the crop. The results of the narrower space tests with the new theory show that their yields are about 19.8% higher than those of the normal ridge planting method.