Sources:Louise Ferguson, G. Steven Sibbett: Olive Production Manual, University of California and Paul M. Vossen: Organic Olive Production Manual<INSERT LINK TO AMAZON.COM>, University of California.
Prior to planting, the soil should be tested for at least sodium, magnesium, calcium, potassium, and pH. If there are questions about the history of the soil, if existing vegetation shows odd symptoms and poor growth, or if other soils in the area have shown toxic levels of excess minor nutrients, more tests may be needed. In addition, if the risk of nematodes or diseases such as Verticillium wilt is suspected, the soil should be tested for those as well.
The pH tolerance of olives is quite large, ranging from about 5 to 8.5. Ideally, it would be adjusted to approximately 6.5, but such adjustments have not been demonstrated to be cost effective. Nor has it been economically worthwhile in most cases to add phosphorus (P) or calcium (Ca) to the soil, since these nutrients are normally in abundance. The exception would be for serpentine soils that are excessively high in Magnesium (Mg). Potassium (K) may be needed for olives, and it can be added prior to planting. Nitrogen is almost always added after planting.
Soils high in boron (Bo), sodium (Na), or chloride should be avoided. Toxic levels of boron, sodium, or other minor elements are not common but have been observed in California.
Multiple sub-samples should be taken from at least two depths with the root zone at about 6 inches and 18 inches deep. This should be done for each observable soil type in the orchard. Do not rely on home soil testing kits. Contact your local farm adviser for a lab recommendation and for a non-biased evaluation of your soil test results. In general, most soil labs will be able to advise you on which tests to run if you tell them what you want to grow and where your land is. Beware of exaggerated yield or plant health claims by fertilizer and compost sales people.
Taking a Soil Sample
Source: Waters Agricultural laboratories, Inc.
Size of Sample Unit
The first step in a sound sampling procedure is to subdivide the area into uniform units. Do not assume that fields enclosed by fences are uniform units. In subdividing a field, use past history and visual differences reflected by changes in soil type for first approximations. Avoid areas where fertilizer or liming materials may have been spilled, gate areas where livestock have congregated, poorly drained areas, or fertilizer band areas of last years crop. It is also advisable to stay at least 50 feet from barns, roads, lanes or fence rows. Within fields that appear uniform, 20 to 25 acres is the acceptable unit size, with the size increasing as the area of uniformity increases.
Of course, the more borings (sub samples) taken within a sample unit, the greater the accuracy of the sample. However , one sub sample per 2-2 1⁄2 acres should be adequate. When sampling, use a zig-zag pattern or random approach and pull cores at least 150 feet apart.
How To Sample
With a spade, trowel, auger, or soil sampling tube, take a thin ver- tical slice or core of soil from at least 10-20 different places in the area to be tested. Combine in a clean plastic bucket, mix thor- oughly, and fill the soil sample bag half full. Fold down and fasten metal flaps securely. The bag should be clearly marked with your name, address, and sample identification. Fill out the soil informa- tion sheet as completely as possible. Be sure the sample numbers on the information sheet correspond with the numbers on the sampling bag. Your soil tests results accuracy will be dependent on properly taken, mixed and submitted samples so please follow these procedures closely.
Click here to see an example of Florida olive soil sample reports.
Click here to download directions for ordering a soil test.