Nitrogen is one nutrient that generally needs to be added regularly to stone fruit orchards in California. It should be managed carefully as both deficiency and excess can cause problems. Deficiency symptoms include a lack of growth and yellow or pale green leaves. Peach and nectarine leaves and stems can develop a characteristic red coloration. Fruit color is often enhanced. Excess nitrogen produces dark green foliage and vigorous shoot growth which results in delayed fruit maturity, decreased red coloration on the fruit, shading out of lower fruiting wood and an increased potential for many pest and disease problems.
A mid summer leaf sample can be useful in managing the optimum nitrogen level so that fruit quality is maximized and excessive vegetative growth is avioded. Peach and nectarine leaves should be between 2.6 and 3.0% (survey) and plum leaves between 2.3 and 2.8%. In most cases these levels can be maintained with annual applications of 25 to 75 lbs N/acre, especially if efficient methods of fertilization are used. Efficient fertilization includes fertigation (applying fertilizer through the irrigation system), split applications, accounting for nitrates in the irrigation water, planting legume cover crops, quickly incorporating or irrigating after a broadcast application, and avoiding applications during the late fall and winter when uptake is minimal. Foliar sprays of urea in the fall can contribute to the total nitrogen needs. In selecting a fertilizer material, consideration should be given to the potential effects of other nutrients in the blend and the effect on soil pH.
Nutrition Chapter in UC Stone Fruit Manual