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XIII. Other Organic and Inorganic Chemicals
3. PMAS (Phenyl Mercuric Acetate)
Recently phenyl mercuric acetate has received attention as a selective
crab grass killer (DeFrance, 1947). Most of the work reported to date
has been on lawns, turfs and golf greens, but successful development of
the material should be a boon in truck gardens and pastures. PMAS is
usually applied as a spray although its action, a t least in part, is through
the soil. I t s selective action on crabgrass may result from the rather
superficial root system of this species.
Developmental work is under way with two other chemicals (Evans,
1948) sodium isopropyl xanthate and ally1 chlorophenyl carbonate, but
little information is as yet available on them.
4. Cyanamid and Cyanate
Calcium cyanamid has long been used as a temporary soil sterilant
to rid soils of weed seeds preparatory to planting lawns (DeFrance, 1948),
tobacco seedbeds (Anonymous, 1948c), and various vegetable and field
crops (Wolf, 1948). Cyanamid dust lias been applied t o cereal crops
as a selective herbicide wherever dew is sufficient to provide moisture to
dissolve the chemical on the leaves of weeds.
More recently potassium cyanate sold under the name of Aero
Cyanate has proved effective as a selective spray in onion and other
bulb crops (Anonymous, 1948d; Evans, 1948). Upon breakdown in the
soil both of these materials leave residues that are high in nitrogen and
hence valuable as fertilizers.
5. CX2, DD, Prochlow
The Irerbicitlal properties of CS2 are well described by Hannesson
et al. (1945). DD (dichloropropane-dichloropropene mixture) proved
effective in the killing of deep-rooted perennial weeds but dosage was
many times that required for nematode control. Since the advent of
2,4-D this material has been limited to the latter use.
Prochlors (chlorinated propane-propene mixture) have been tested as
weed killers (Freed, 1947) but have not been widely used. They offer
some advantages over CS, but cost considerably more than 2,4-D in the
control of perennial weeds,
While generalization as to new chemicals in a field as fluid a s that
of herbicides is not without risk, nevertheless certain trends do appear.
Specific selectivities, undreamed of a few years ago, have aIready emerged
and become an integral part of the agricultural scene. More such selective chemicals are in the offing, bringing further advances in weed control. Also, new developments point to better grass killers both as
A. 8. CRAFTS AND W. A. HARVEY
selectives and general toxicants and the resultant decrease in the use of
oil for this purpose. The major impact of herbicides on agricultural
practices is yet to be felt.
6. Arsenic, Borax, Chlorate
Because litt.le has been added to the information given in Robbins
et al. (1942) on these herbicides, they will receive only passing mention
here. There are still many situations in which they are useful, but full
knowledge concerning their properties is required for their intelligent
Of importance to irrigation agriculture are the new chemical methods
for controlling semi-submersed and submersed water weeds. I n place
of chaining, dragging, and cutting by various means, methods that
tended to subdivide the plants and spread the infestations, treating the
irrigation water with chlorinated benzenes or solvent naphthas has proved
effective and relatively inexpensive (Crafts, 1945a; Hirst, 1947; Moran
and Shaw, 1948). The chemicals, mixed with sufficient emulsion stabilizers to insure immediate emulsification, are sprayed under the surface of
the flowing water in the ditch. They form milky white emulsions and
the toxicants are absorbed by the leaves of the weeds, resulting in rapid
plasmolysis and death. The chlorinated benzene killers are heavier than
water and they tend to settle into the mud in the ditch bottom, resulting
in a slight residual effect. The solvent naphthas, being lighter than
water, rise to the surface when the emulsions break.
The rapid expansion of chemical weed control has created a big
demand for equipment. One company sold over two million nozzles during the 1948 spraying season and this represents only a small fraction
of the total business. Because of the great demand, many State Agricultural Experiment Stations have printed bulletins or circulars describing equipment. The following references provide a number that will be
found convenient (Akesson and Harvey, 1948; Anonymous, 1948k ; Derscheid and Stahler, 1948; Price et al., 1946; Sylvester and Bakke, 1947).
As a corollary to the introduction of new pest control chemicals come
abuses, misuse, and accidents. Already 2,4-D has damaged thousands
of acres of cotton, tomatoes, beans, sweet potatoes, melons, and grapes,
and many people are ready to prohibit its sale and use. To those who
remember t.he numerous cases of arsenic poisoning, chlorate burns and
other accidents, this is simply evidence of the lag of popular education
behind the promotion and sales of these materials.
Most of the cases of serious damage such as those occurring in Texas
and Louisiana (Brown, 1947s; Dunlap, 1948; Staten, 1946), and that of
the San Joaquin Valley in California in 1948 (Pryor, 1948) are obviously
examples of misuse. They can be prevented in t.he future by proper
instruction of growers in the precautions essential to the use of so potent
Of more interest and concern to the agronomist are certain cases
involving secondary effects. I n one instance in California, either bull
thistle or milk thistle plants sprayed with 2,4-D proved fatal to lambs.
Several people have been reported as exhibiting allergic symptoms as a
result of contact with 2,4-D. One instance of allergic reaction to mayweed sprayed with 2,4-D has been noted. These cases are serious and
deserve careful study.
On the other side, curly dock plants in a ladino clover pasture that
had received a 2,4-D spray were so relished by sheep that they were
eaten clear into the ground. And many tests in the greenhouse with
2,4-D in soils show stimulation of crop plants by as much as 100 per
cent after the chemical has broken down in the soil (Crafts, 1949; Tullis,
Breakdown of 2,4-D in soils has been shown to be related to the
activities of microorganisms (DeRose and Newman, 1947; Newman,
1947). Recent work indicates that the soil microflora may be altered by
the presence of 2,4-D so that subsequent applications of the chemical are
destroyed more rapidly than the initial treatment. This is of great
significance in preemergence practice as too rapid disappearance of the
chemical may reduce the effectiveness. Another prominent effect of
2,4-D use is the build-up of grassy weed populations. Already some
growers are complaining about the increase in wild oat populations in
their grain fields. One case has been reported in California where
elimination of bur clover by 2,4-D treatment has seriously reduced the
value of the stubble as sheep pasture. These examples illustrate the
far-reaching effects that can be expected from sudden changes as drastic
as that of weed elimination. I n all tests on new herbicides the investigator should be constantly on the watch for such secondary effects. Only
by vigilance can serious accidents be prevented and full usefulness of
the new materials be exploited.
A. S. CRAFTS AND W. A. HARVEY
The use of weed burners to control weeds selectively in growing crops
has received attention in several areas.. Probably the widest agronomic
interest has been in cotton where mechanization has been a prime motive
in the development of flame weeding (Neely and Brain, 1944). The
selectivity of the method is based on the greater resistance to heat of
cot.ton stems which become woody more rapidly than the stems of succulent weeds. Thus it is possible to find a time of exposure to a particular temperature which will kill young weeds but not permanently
injure cotton. Such selectivity is only relative and too long an exposure
to flaming when cotton is too small will injure the crop. The method
is still in the developmental stage (Grigsby, 1948), although some plantations are flaming a substantial acreage.
Other crops on which flaming shows promise include corn and sugar
cane, where the enfolding outer leaves protect the stem from injury. A
few truck crops (i.e.J onions) and ornamentals (lilies) also withstand
The use of flame as a preemergence treatment has also received attention. In this respect, flaming competes directly with herbicides and
the choice may become one of cost and convenience.
XVIII. THENEW AGRONOMY
Under the above title we should like to discuss some of the ideas that
are evolving with the use of the new, highly effective herbicides. Many
practices involving rates of seeding, spacing of drill rows, harrowing and
fertilization have grown up around the problems of weed control. The
width of rows and the spacing of seeds in the rows of intertilled crops
have been dictated by the length of the single-tree or the prescribed
spacing of implements on the tractor drawbar (Norman, 1948).
Since the introduction of 2,4-D the eminent success in the control of
weeds has suggested to many the possible alteration of such practices
with increased crop production as the goal, using mechanized pest control
and mechanized harvesting in place of conventional methods. I n recent
t.rials, in which 200 bushels or'more of corn per acre were produced
(Anonymous, 1948i), several of the successful growers used 20-inch rows
with 6 to 9 inch spacing within rows. This provides a more uniform
environment. Similar spacing trials are being tested in cotton, soy beans,
and other intertilled crops (Leonard et al., 1947, 1948).
By using close spacing, mechanized pest control, and increasing the
fertilieer applicat.ion, not only are crop yields being increased, but tillage
with it,s attendant root pruning and its deleterious effects on soil colloids
is reduced to a minimum. This allows the soil to attain as nearly its
virgin fertility as is possible under a cropping regime, and it appreciably
lowers losses from erosion and leaching. Use of segmented or pelleted
seed and precision planting are adding t o the degree of control which
the grower is able t o exercise over his crops (Bainer, 1947, 1948). These
two features alone may cut the need for hand weeding almost t o zero.
Furthermore, the various organic materials used in pest control are
broken down in the soil, with a resultant increase in fertility (Zobel,
1946). Many of the toxicants, after breaking down, seem to have a
stimulatory effect on the crops (Crafts, 1949). How far the grower can
go in combining these various effects to increase yields is difficult to
foresee, but it. seems certain that when they are used t o their maximum
advantage many of the soil losses that have been stressed by soil conservation workers will be eliminated. This will mean that instead of
facing a future of constantly diminishing returns from the soil, crop
production may be maintained a t least a t its present level and possibly
may be raised to an appreciable extent.
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Boron in Soils and Crops*
K . C . BERGER
I . Introduction . . . . . . . . . . . . . . . . . . . . . . . .
I1. Boron Determination . . . . . . . . . . . . . . . . . . . . .
1. Titrimetric Procedures . . . . . . . . . . . . . . . . . . 323
2. Spectroscopic Methods . . . . . . . . . . . . . . . . . . 323
3. Colorimetric Methods . . . . . . . . . . . . . . . . . 324
a . Turmeric Test . . . . . . . . . . . . . . . . . . . 324
b . Hydroxyanthraquinone Tests . . . . . . . . . . . . . . 325
c . Quinalizarin Test
. . . . . . . . . . . . . . . . . . 325
4. Biological Methods . . . . . . . . . . . . . . . . . . . 326
I11. Boron Availability in Soils . . . . . . . . . . . . . . . . . . 327
1 . Conditions Favoring Availability . . . . . . . . . . . . . . 327
a . Organic Matter . . . . . . . . . . . .
. . . . . . 328
b . Lack of Leaching . . . . . . . . . . . . . . . . . . 329
c. Texture . . . . . . . . . . . . . . . . . . . . . .
2. Conditions Favoring Fixation or Loss . . . . . . . . . . . . 329
a . Alkalinity and Change in pH . . . . . . . . . . . . . 330
b . Calcium-Boron Ratios . . . . . . . . . . . . . . . . 332
c. Leaching . . . . . . . . . . . . . . . . . . . . . .
d . Drying . . . . . . . . . . . . . . . . . . . . .
e . Crop Removal . . . . . . . . . . . . . . . . . . . 334
3. Boron Cycle . . . . . . . . . . . . . . . . . . . . . .
IV. Boron Requirement of Plants . . . . . . . . . . . . . . . . . 336
1. Function of Boron in Plants . . . . . . . . . . . . . . . . 337
2. Interrelations with Other Elements . . . . . . . . . . . . . 338
a . Calcium-Boron Ratios . . . . . . . . . . . . . . . . 339
b . Potassium-Boron Ratios . . . . . . . . . . . . . . . . 340
c. Nitrogen-Boron Relationship . . . . . . . . . . . . . . 341
d . Other Elements . . . . . . . . . . . . . . . . . . . 341
3. Symptoms of Boron Deficiency . . . . . . . . . . . . . . . 342
4. Boron Requirements of Plants . . . . . . . . . . . . . . . 344
V . Summary . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . .
I . INTRODUCTION
Although borax. under the name of Tincal or Tincar. was exported to
Europe from central Asia and was used before the middle of the sixteenth
* Contribution from the Department of Soils. University of Wisconsin. Madison.
Wis . Published with the permission of the director of the Wisconsin Agricultural
Experiment Station .