Regular leaf sampling for nutrients can be a valuable tool for diagnosing nutritional problems in the orchard and also evaluating the effectiveness of one's fertilization program. The standard procedure (click here to read about an experimental dormant sampling procedure) is to collect 60 to 100 leaves randomly throughout the orchard in June or July. For peach and nectarine, sample midshoot leaves on moderately vigorous current season shoots (10 to 20 inches long). For plum, sample leaves from non-fruiting spurs. After drying the samples, send them to a commercial lab for nutrient analysis.
The table at the right indicates optimum ranges for each nutrient. Deficency and toxicity thresholds are also indicated if known. (We have proposed changing some of these thesholds based on research with the sand tank trees - Refining Deficiency Levels)
Further Reading
UC Bulletin by Beutel, Uriu and Lilleland
Nutrition Chapter in UC Stone Fruit Manual
Below are graphs from a survey of 60 healthy commercial orchards sampled in July 2004. Note that only nitrogen and zinc were deficient in any of the orchards. Some orchards also showed higher than optimum nitrogen levels. Click on the graph to enlarge.