July to September is the optimum time to collect citrus soil and leaf samples for analysis. Soil and leaf sampling are key components in the evaluation of a citrus nutrition program and required Citrus Best Management Practices recordkeeping documentation.
Annual sampling and its analysis provide a good idea of the nutritional trends that have been occurring within specific grove blocks from year to year. Always retain records for all soil and leaf analysis results.
Select representative trees from each grove block that will be managed nutritionally the same way. Typically, 15 to 20 trees are selected for leaf and soil sampling. Growers can reduce variability in analysis interpretation by utilizing samples from the same trees from one year to the next. Take advantage of the availability of affordable GPS technology to sample the same trees every year.
SOIL
Soil analysis can provide very specific information for use in nutritional program decision making. This information includes soil pH, phosphorous, calcium, magnesium and copper (if you specifically request the copper analysis).
From the 15 to 20 trees sampled, take a single soil core of an 8-inch depth from within the irrigation pattern of each tree. Place the sampling cores in a clean nonmetal bucket for collection. Thoroughly mix the sample cores together. Use approximately one pint of the soil from the mixed sample for analysis.
Not all soil testing laboratories use the same extraction procedures to determine soil nutrient levels. Growers may consider sending samples from the same bucket to different labs to compare results. Growers who change soil testing labs from one year to the next, or utilize different extraction methodologies, should understand how to properly interpret the results and appropriate tables.
LEAF
Leaf analysis can be utilized for all essential elements including those determined in the soil analysis. Leaf samples should be collected from the same trees as the soil samples. One hundred healthy and representative leaves from the 15 to 20 trees should be collected. These leaves should be four to six months old from non-fruiting twigs. Keep the collected leaves out of the heat. If they cannot be sent out immediately, place them in a refrigerator for overnight storage.
For macronutrient analysis, the leaves need not be washed. If micronutrient analysis is desired, the leaves will need to be washed well to remove surface contamination. Washing of leaves can be done by soaking them in a mild detergent solution and rubbing them between thumb and forefinger. The washing of leaves should be done as soon as possible after collection.
Copper, manganese and zinc are exceedingly difficult to remove through surface washing. This should serve as a reminder that it may be exceedingly difficult to make judgments utilizing leaf analysis if growers are applying frequent nutritional sprays.
Source: Highlands County Citrus Growers Association
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