Sampling Procedures for Foliar Analysis
UCCE Farm Advisor, Kern County
Deciduous Tree Fruits and Nuts
June 15, 2000
SAMPLING PROCEDURES FOR FOLIAR ANALYSIS
Foliar tissue analysis is a chemical test that determines essential or toxic levels of nutrient in leaves. It is used as a means of 1) detecting tree response to fertilizer programs, 2) determin-ing nutrient-element deficiencies or toxicities, and 3) estimating fertilization needs prior to nutrient deficiency symptoms.
The results of a leaf analysis can't be better than the sampling and analytical procedures used. Therefore, proper sampling and a reputable laboratory are an integral and vital part of foliar analysis.
A good sampling procedure must consider the sampling unit, leaves to sample, the amount of leaves and sample handling. The uniformity of the orchard will determine the sampling unit. Ideally, every twenty acres of an orchard, every soil type and every variety should be sampled separately. Growers, however, prefer to sample problem blocks and take a few samples each year from good blocks. They are very careful in one aspect, and make sure that each sample is collected from representative trees of the entire sampled area.
The pattern of sampling should be the same, if leaf analysis results are to be compared year after year. Ideally, leaf samples should be taken from the same tree in the same row every year. Avoid samples from problem areas (diseased, injured, replants, odd varieties or off-type trees) except for diagnostic purposes. If this is the case, the sample should be kept separate.
Uniformity of sample is important, particularly where comparisons are being made. One can achieve this by sampling fully expanded, mature leaves from non-fruiting spurs. In the case of non-spur forming trees, such as peaches and nectarines, collect mature leaves from the lower half of current season's shoots. In walnuts, take the terminal leaflet of the compound leaf on the mid section of a moderately growing shoot. For pecans, the sampling procedure consists of sampling the middle pair of leaflets from the compound leaf on the mid-portion of the shoot. Leaves that are water deficient or have been damaged by spider mites should not be included in the sample. Their nutrient levels will be lower than healthy leaves.
If one is interested in micronutrient levels, one shouldn't select leaves that have been sprayed with foliar nutrient sprays. The reason being that minor element spray deposits can't be removed well enough to trust the analysis.
Each leaf sample should be large enough to adequately represent the orchard. The leaf size will determine the number of leaves for each sample. For almonds and apricots, 100 leaves are needed. In fruits and nuts species such as apples, peaches, pears, nectarines and pecans, 60 to 80 leaves are needed for the analysis. Water samples only require 30 to 40 leaflets.
The best time to take the leaf sample is during June and July. At this time, most leaves are fully developed and their nutrient concentration is stable. However, samples may be taken in August or September, but interpretation of the results must be adjusted for seasonal effect. The leaves should be collected in plastic or paper bags and stored in a portable ice chest. Leaves in plastic bags must be kept cool and protected from direct sunlight. The bags should be labeled with the following information: date, orchard location and tree location (tree and row number).
Leaf tissue analysis is not a substitute for visual observations but is simply a tool to use for a sound fertilization program. In most cases, it will confirm toxicity and/or nutritional problems in the orchard.
Please note the following correction in the news release of June 7, 2000, The Glassy-Winged Sharpshooter and the Homeowner:
Page 2, sixth line from the top, a typographical error describes the leafhopper as approximately two inches long. It should be approximately 1/2 inch long.
We apologize for any inconvenience this may have caused.