USING DORMANT SHOOTS TO DETERMINE THE NUTRITIONAL STATUS OF PEACH TREES

Nutrient analysis of leaf samples taken in mid summer has been as a standard practice for assessing the nutritional status of fruit trees throughout the world. This timing was originally proposed because most nutrient levels remain fairly stable for an extended period, thus creating a wide window for sampling. However, it is generally too late in the season to assist in making fertilization decisions regarding the crop for that year. Instead, orchard managers are much more interested in evaluating the condition of their trees early in the season when they can still influence parameters such as fruit set, shoot growth, fruit growth and fruit quality. Therefore, it would be very useful to be able to measure the nutritional status of fruit trees early in the spring and develop sufficiency ranges for each nutrient. Researchers have been able to do this with some success using flower and early leaf samples. The goal has been to evaluate the nutritional status of dormant shoots and relate it to various parameters of tree performance and productivity. The information was obtained from 60 ‘Zee Lady’ peach trees and 60 ‘Grand Pearl’ nectarine trees growing in large sand tanks since 2000. Applying fertilizer salts at differing rates has resulted in trees varying substantially in most nutrients. Many measures of tree performance have been taken including flower density, fruit set, early shoot growth, fruit size at thinning time, final fruit size, fruit quality and total vegetative growth. Visual ratings were also made of different leaf symptoms and levels of defoliation. Many of these parameters related well to nutrient levels measured in dormant shoots sampled in January or February of 2003 and 2004. Thus, good relationships have been obtained for nitrogen (N), phosphorus (P), boron (B) and zinc (Zn), and tentative deficiency thresholds have been proposed. Some of the other nutrients have not shown good relationships, mainly because distinct deficiency symptoms have not yet been induced. So far, this approach generally shows great promise as a tool to help peach growers fine tune the fertility program in their orchards.