The Rural Voice, 1981-05, Page 29GUEST COLUMN
Test your soil's atrazine level
Robert Forrest. Agronomy Division. Cen-
tralia College of Agricultural Technology.
Any farmer who grows corn probably uses atrazine to control
weeds in his crop. and if he practices crop rotation he must know
the level of atrazine in his ;oil before rotating to a non -tolerant
crop.
Many farmers rent land from time to time. Very few rental
agreements state the levels of pesticide residues in the soil. A
simple bioassay would allow the rentor to determine if the
residue was at a safe level for the crop he wished to grow.
A simple bioassay may be conducted in ,a greenhouse or in the
farm kitchen. A basic understanding of how atrazine works,
however. is necessary in order to arrive at the proper
conclusions.
Atrazine is one of a family of triazine products and as such, it
works within some plants to inhibit the photosynthetic process.
Photosynthesis is the process within a plant that produces
carbohydrate. and hence plant growth. If this process is
disrupted, the plant ceases to grow and usually dies.
Atrazine in the soil must be picked up by growing roots to gain
entry into the plant. When seeds are planted in the soil the
starch stored in the endosperm will support the growth of that
seedling for some time. Barley, for example. is affected very
little by atrazine until it runs out of starch in the seed, and its
root system is established.
Soil -applied atrazine breaks down through the activity of micro
organisms. A small amount may leach to lower regions of the soil
profile. The micro organisms that degrade or break down
atrazine work most rapidly in warm. moist soil. Therefore the
weather. length of growing season and time of application play
an important role in the breakdown process. Since the micro
organisms continue to work, although very slowly, through the
fall, it is best to do a residue analysis in early spring.
The procedure is not difficult. Use a soil probe and sample the
top 15 cm of ;coi1(plow depth.) Collect about 7 or 8 litres of soil for
each test. Place the soil in a plastic tray or pots with good
drainage. Plant one third of each flat (or pots) with each of the
three following crops: barley, white (or kidney) beans and
cucumber. Plant a second flat (or pots) with the same three
crops, but use soil of the same type, but known not to contain
pesticide residues.
Water lightly, as needed. Over -watering tends to move the
atrazine residues out of the soil. Observe Inc seedlings daily for
at least three weeks. Barley must reach the 5 -leaf stage. and
beans must reach the 3-4 trifoliate leaf stage. This allows the root
systems time to develop and take up any residues present.
Atrazine damage causes a whitening of the tip of the oldest
(lowest) leaf in barley. The whitening spreads along the edges of
the leaf, and finally the leaf dies. Higher concentration of residue
will cause damage that progresses upward on the plant. In beans
and cucumber, similar whitening around the leaf margins results
from atrazine uptake. This whitening then spreads over the
remainder of the leaf.
The plants grown in the residue -free soil should grow
normally. They are included in the test to be sure that any
symptoms noted on the plants grown in the suspect soil are
indeed due to herbicide residues and not to other variables, such
as over -watering, which would affect both.
As a final check, add additional stress to the plants by
reducing watering. Atrazine residues will affect plants more
severely when they are under stress.
The three different crop species are used to give an indication
of the quantit y of any residue present. Barley is fairly tolerant to
atrazine residue, while beans have considerably less tolerance,
and cucumbers are highly susceptible to atrazine at very low
levels.
Using this simple test. a farmer can get a good indication of
the amount of atrazine residue in his soil and can make
intelligent decisions regarding the advisability of growing a
sensitive crop on land previously treated with this herbicide.
HOW IT WORKS;
20" disc. blades. mounted on individual pivots, are
rotated by hydraulic motors to cut bean plants off
below ground surface. Each pivot -mounted section
rests on two depth wheels. Two or three windrows
are produced, depending on the number of blades.
The Smyth Bean Cutter can be mounted on the front
or on the rear of a tractor. This compact machine is
not bothered by mud or trash.
Canada's first rotary bean cutter is a product of
the George Smyth Welding and Machine Shop.
THE FIRST NEW IDEA IN BEAN
PULLING IN 70 YEARS
SMYTN
Welding and
Machine Shop
RR 2, Auburn, Ontario (519) 529-7212
THE RURAL VOICE/MAY 1981 PG 27