Does Your Soil Make the Grade?
Soil Tests Reveal A Lot About Your Organic Garden's Soil
Mysterious crop failures, stunted, withered plants and insect
pest infestations can all be symptoms of a garden soil in need
of some help. A
soil test is an excellent tool for assessing the
health of your soil and will help you develop a "soil fitness
plan" for your organic garden. Most states in the US offer free
or low-cost soil testing and, no, scientists don't come out and
give your soil a quiz. The soil testing process begins with you
collecting a soil sample and getting it to your state's soil
Most soil testing labs have special boxes and instructions for
you to use and follow when taking your soil sample, but the
general procedure is for you to take some soil from various
locations in your garden, mix all the soil together and then get
some this "homogenized soil" to the testing lab, either by mail
or by bringing your sample in person. Soil testing labs usually
require about 1 cup of soil in order to perform their analysis.
Once your sample arrives at the lab, teams of dedicated soil
scientists will catalogue it, oven dry it and then get busy
learning all about your soil so that they can give you valuable
information about it. Here are some of the things that a typical
soil testing lab assesses:
Soil pH -- soil pH indicates how acidic (or alkaline) your soil
is. This is important to know because all plants have pH ranges
in which they grow best. If the pH of your soil isn't right for
the type of plants that you are trying to grow, you will have a
real uphill battle on your hands.
Buffering Capacity-- This measurement indicates how resistant
your soil will be to attempts to change its pH. For example, the
pH of soil with a low buffering capacity can be increased with a
lot less lime (a soil amendment used to decrease soil acidity)
than a soil with a high buffering capacity.
Soil cation exchange capacity (CEC)-- Most of the nutrients that
are essential to plant growth exist in the soil in the form of
positively-charged ions, which are known as cations. Sodium,
potassium, Calcium, Magnesium are only a few examples of the
plant-essential cations that are present in your soil. CEC is
simply a measure of how many of these important cations your
soil can hold. The higher your soil's CEC, the better.
Base Saturation-- The base saturation number on your soil test
report tells you what percentage of your soil's CEC is used up
by Calcium, Magnesium and other basic ions. Base saturation is
generally directly linked to soil pH: when base saturation is
high, pH goes up, when it is low, pH goes down (becomes more
acidic). Your base saturation can help you pinpoint the source
of soil structure or nutrient availability problems in your
organic garden's soil.
Percentage of Organic Matter-- Organic matter is one of the most
important ingredients that goes into making a healthy soil.
Organic matter promotes good soil structure, which leads to good
water holding capacity. Organic matter can hold lots of
nutrients, which increases your garden soil's CEC. It also
encourages beneficial creatures such as earthworms to make your
organic garden their home. In general, the more organic matter
you have in your soil, the better. The percent organic matter
measurement tells you how much of your soil is made up of
organic matter. Ideally, this number would be at least 5%,
although some soils are naturally much higher in organic matter
than this and others (sandy soils, in particular) often contain
much less than 5% organic matter.
As you can see, a soil test can explain a lot about your soil.
It will let you know what you should do in order to make your
soil healthier: most soil test results also include customized
recommendations for how to help you grow the crops of your
choice. It also will remind you just how amazing and complex
your garden's soil is and, if for no other reason than that, it
is worth getting one!
For More Information:
New Mexico Stateís guide to interpreting soil test results. It
is particularly useful if you live in the Southwest US, but also
has information that applies to soils everywhere.
This links to a list of alternative soil testing labs: if you
want your soil tested for things that arenít tested for at your
stateís lab, such as microbial biodiversity, or if you want your
fertilizer recommendations given to you based on application
rates for organic fertilizer, send you soil to one of the labs
on this list.