Selecting a Winning Site and Crops to Match - Growing Organic Orchard Fruits - page 34

in the soil but is in a chemical form that is unavailable to the trees. Excess-
ive concentrations of some other nutrients, such as phosphorus, can interfere
with the uptake and utilization of iron. Iron chlorosis is particularly common
on wet, cold soils.
Orchard soils can be acidified and iron can be added to the trees in foliar
sprays, but these practices increase the work and costs of the establishment
and maintenance of the orchard. By far the best orchard sites have well-
drained soils with pH values roughly between 5.5 and 7.5. We'll discuss how
to adjust soil pH in chapter 4 ➔ . For now, be aware that growing fruit crops
on soils with a pH above about 7.5 is more difficult than doing so on neutral
or slightly acidic soils.
Soil Salinity
Salty (saline) soils can be a problem in some regions of North America, par-
ticularly on arid sites. Even in areas with relatively abundant precipitation,
saline soils can develop due to excessive applications of fertilizers, including
manures. Frequent, shallow irrigation dissolves salts and concentrates them
near the soil surface as the water evaporates. Many horticultural crops are
sensitive to high concentrations of salts and perform poorly on such soils.
Soil salinity is measured with electrical conductivity meters. Reporting
units vary from one laboratory to another and include micromhos per cen-
timeter ( µ mho/cm), millimhos per centimeter (mmho/cm), deciSiemens per
meter (dS/m), and a few other units. Fortunately, it is easy to convert
between units: 1000 µ mho/cm = 1 mmho/cm = 1dS/m.
Soils with salinity levels of 0 to 2,000 µ mho/cm (0-2 mmho/cm or 0-2
dS/m) are considered nonsaline and are suitable for all crops. Salinity levels
between 2,000 and 4,000 µ mho/cm (2-4 mmho/cm or 2-4 dS/m) indicate a
very slightly saline soil and can create problems in sensitive plants, includ-
ing blueberries, raspberries, and strawberries. Tree fruit crops tolerate very
slightly saline soils better than their berry counterparts and can generally
be grown on soils with salinity levels of 4,000 µ mho/cm or less (4 mmho/cm
or 4 dS/m), providing the soils are otherwise acceptable. For soils with salin-