The history of nitrogen usage on oranges in California shows that prior to about 1960 many growers were using more nitrogen than was needed to produce the crop. In some areas nitrogen usage is now less than half of what it was prior to 1960. The reduction was associated with increased commercial usage of leaf analysis as a guide to nitrogen fertilization. Also since 1960, as a result of the decrease in fertilizer applied, the annual per‐acre amounts of fertilizer nitrogen that were subject to leaching in the Santa Ana Watershed were reduced by an estimated 50 percent in Riverside County and about 80 percent in San Bernardino County.