In a situation
such as this, a basic soil audit is the first and sometimes the only monitoring
tool used to assess changes in the soil. Unfortunately, the standard soil test
done to determine nutrient levels which are P, K, Ca, Mg, and so on, do provide
no information on soil biology and physical properties. A better appreciation
of these biological and physical soil properties, and how they affect soil
management and productivity, has resulted in the adoption of several new soil
health assessment techniques which are discussed below.
The USDA soil quality test kit
The USDA soil
quality Institute provides a soil quality test kit guide. The kit was designed
for field use. Components necessary to build a kit include many items commonly
available such as pop bottles, flat bladed knives, a garden trowel, and plastic
wrap. Also necessary to do the tests is some equipment usually not locally
available such as hypodermic needles, latex tubing, a soil thermometer, an
electrical conductivity meter, filter paper, and an EC calibration standard. The
kit allows the measurement of water infiltration, water holding capacity, bulk
density, pH, soil nitrate, salt concentration, aggregate stability, earthworm
numbers, and respiration.
Early warning monitoring for crop lands
The monitoring
guide contains a set of soil health indicators that are measurable in the crop
land. No fancy equipment is needed to make the assessments described in this
monitoring guide. In fact, all the equipment is cheap and locally available on
almost any farm. Simple measurements can help determine the health of crop lands
in terms of the effectiveness of the nutrient cycle, water cycle, and the
diversity of some soil organisms. Some of the assessments you can make using
this guide are living organisms, aggregation, water infiltration, ground cover,
and earthworms.
Direct assessment of the farm soil health
Some quick ways
to identify a healthy soil include feeling it and smelling it. Grab a handful
and take a whiff. Does it have an earthy smell? Is it a loose, crumbly soil
with some earthworms present? Look at the surface and see if it is crusted,
which tells something about tillage practices used, organic matter, and
structure. Pushing a soil probe down to 12 inches, lift out some soil and feel
its texture. If a plow pan were present it would have been felt with the probe.
Turn over a shovelful of soil to look for earthworms and smell for
actinomycetes, which are microorganisms that help compost and stabilize
decaying organic matter. Their activity leaves a fresh earthy smell in the
soil. There are two more easy observations which are to count the number of
soil organisms in a square foot of surface crop residue and to pour a pint of
water on the soil and record the time it takes to sink in.
A simple erosion test in the farm
This test
demonstrates the value of ground cover. Tape a white piece of paper near the
end of a 3-foot-long stick. Hold the stick in one hand so as to have the paper
end within 1 inch of a bare soil surface. Now pour a pint of water onto the
bare soil within 2-3 inches of the white paper and observe the soil
accumulation on the white paper. Tape another piece of white paper to the stick
and repeat the operation, this time over soil with 100% ground cover, and
observe the accumulation of soil on the paper. Compare the two pieces of paper.
This simple test shows how effective ground cover can be at preventing soil
particles from detaching from the soil surface.
Detachment of
soil particles occurs when falling rain water collides with bare ground. After
enough water builds up on the soil surface, following detachment, overland
water flow transports suspended soil down slope. Suspended soil in the runoff
water abrades and detaches additional soil particles as the water travels
overland. Preventing detachment is the most effective point of erosion control due
to the fact that it keeps the soil in place. Other erosion control practices
which seek to slow soil particle transport and cause soil to be deposited
before it reaches the stream are less effective at preventing erosion.
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