Decline in production and in size of fruit is an increasing problem in southern California's citrus groves. Package plot experiments, under way for some time, have not solved that problem, but they have provided promising leads. This report is concerned with one phase of the project—the effect of various treatments on production, fruit size, and the physical properties of the soil within the plots. Treatments were made in: navel orange groves at Redlands, Highlands, and Riverside; Valencia orange groves at Olive and Santa Paula; and a lemon grove at Ventura. Two replications of four tree plots were used in the groves at Redlands, Highlands, and Olive; four replications of four tree plots were used at Ventura and Santa Paula; and five replications of two tree plots were used at Riverside.