Nutrient Management - Growing Organic Orchard Fruits - page 381

lished, soil tests for nutrient concentrations become much less useful, for
several reasons: Trees and fruit bushes have spreading root systems that
gather nutrients from large volumes of soil. These plants are also very effi-
cient at concentrating mineral nutrients in their tissues at much higher con-
centrations than are found in the soil. And unlike annual crops that grow
and die in a single season and release the nutrients back into the soil, woody
plants recycle and store nutrients from year to year. For these reasons, soil
nutrient tests on established orchards often correlate poorly with fruit crop
performance.
It is important to test your soil's pH levels throughout the life of the orch-
ard. Remember that soil pH has a strong impact on nutrient availability,
as shown in figure 4.6 ➔ . An excellent goal is to maintain the pH between
6.0 and 7.0 and as near 6.5 as possible, recognizing that soil pH varies
throughout the year. Soil pH also varies across the orchard. Research has
shown that soil pH in the planting row often differs significantly from the
pH within the alley, just a few feet away.
Plan on testing the soil within crop rows every 2 to 3 years. While the
time of sampling is not critical, you should sample at the same time each
year because soil pH varies with the seasons. I normally sample the soil in
mid-spring, when plant growth is most rapid and the need for plant nutrients
is the greatest. See box on page 260 ➔ for how to collect a sample.
When gathering samples, an easy approach is to walk diagonally from
one corner of the orchard or planting block to the opposite corner, sampling
as you cross tree rows. Repeat the process on the other diagonal to obtain a
representative sample for that block. Mix the samples inside the plastic pail
and take out enough to fill the sample bag provided by your testing laborat-
ory. If you are concerned about the pH effects on alley crops, you may want
to repeat the procedure along the centers of the alleys.
Many universities with agriculture programs offer soil testing, and there
are many good private laboratories in the United States and Canada. Choose
a laboratory as close as possible to your site. Soil testing procedures vary
greatly from one region to another, based on different soil types. Always use