Agriculture Reference
In-Depth Information
this, the "fizz test" described above, where ordinary vinegar is added to the soil, is
recommended. If the soil bubbles when vinegar is added, you will want to get an
AA8.2 test in addition to the essential M3 test.
Another indicator that one should get anAA8.2 test for a soil with pH <7 is if the
Mehlich 3 test shows a surprisingly high level of Calcium and estimated CEC.
Calcareous sands will generally have a low CEC, often as low as 2 or 3meq, when
tested with theAA8.2 test. If theAA8.2 test shows a CEC >7meq and a pH <7,
they may be treated the same as any other soil with a pH <7, according to the
ratios shown on the Ideal Soil Chart. If they have a CEC < 7meq, they should be
treated as shown in the following chapter on Low CEC Soils.
Mineral Availability in High pH Soils
The availability of essential minerals such as Fe, Mn, Cu, Zn, and Pcan be poor in
high pH soils because the metallic elements readily combine with OH- ions,
forming insoluble hydroxides, while P combines with available cations forming
insoluble phosphates. Often this problem is addressed by applying these
elements in soluble form as sulfates, chlorides, or nitrates via fertigation, foliar
spraying, banding of soluble fertilizers in the seeding row, or by using small
amounts of the elements chelated with EDTA.
In the 4
th
century BCAristotle wrote that "the soil is the stomach of the plants,
digesting and making food available".As in our own bodies, it is the beneficial
microorganisms that do much of the work of digestion and chelation of essential
minerals.
One significant benefit of having the minerals in balance in the soil is that it
encourages the growth of beneficial soil organisms that can access poorly soluble
nutrients and chelate them biologically.As the soil organisms go through their life
cycle, the minerals they have chelated become available to plants. Mycorrhizal
fungi have been shown able to achieve a pH<2, which can solubilize practically
any mineral complex in the soil and make it available.
It has been our experience that if the anions N, P, Cl, and especially S are
maintained at Ideal Soil ratios, along with a optimum level of organic matter in a
biologically active soil, the metallic elements and P will remain available to the
crops without resorting to spoon-feeding.
