This dissertation has been 62—817 microfilmed exactly as received
STROUBE, Edward White, 1927- THE MOVEMENT AND PERSISTENCE OF SIMAZINE AND ATRAZENE IN SOIL AND SOME RELATED STUDIES.
The Ohio State University, Ph.D., 1961 Agriculture, plant culture
University Microfilms, Inc., Ann Arbor, Michigan THE MOVEMENT AND PERSISTENCE OF SIMAZINE AND ATRAZINE IN SOIL
AND SOME RELATED STUDIES
DISSERTATION
Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University
By
Edward White Stroube, B.S., M.S.
-i «
The Ohio State University 1961
Approved by
Department of Agronomy ACKNOWLEDGMENTS
The author gratefully appreciates the guidance and direction given by Drs. D. D. Bondarenko and C. J. Willard in the course of this study. Sincere appreciation is also extended to Drs. S. R. Anderson,
E. K. Alban, D. A. Ray and P. E. Smith for their helpful suggestions and constructive criticisms during the preparation of this manuscript.
The author wishes to thank the faculty and staff members and fellow graduate students of the Department of Agronomy for their inter est and assistance during the course of this study.
Gratitude is expressed to the Geigy Chemical Corporation for some of the materials used in this investigation.
The author is deeply grateful to his wife for the encouragement, assistance and sacrifices made by her during this study.
ii CONTENTS
Page
INTRODUCTION ...... 1
REVIEW OF LITERATURE ...... 3
The effectiveness of simazine as an herbicide when applied to corn...... 3
The movement and persistence of herbicides in so i l s ...... 8
The effect of herbicides on soil microorganisms...... 18
EXPERIMENTAL MATERIALS AND METHODS ...... 22
Properties and source of herbicides ...... 22
? The effect of simazine on weed population and corn yield. . . . 23
The effect of simazine soil residues on corn, wheat, barley, oats and soybeans ...... 25
The movement of simazine in soil in the fie l d ...... 28
The movement of simazine and atrazine in soil in the laboratory...... 29
The effect of soil microorganisms on the breakdown of simazine and the effect of simazine on the activity of soil micro organisms ...... 33
EXPERIMENTAL RESULTS AND DISCUSSION...... 36
The effect of simazine on weed population and corn yield. . . . 36
The effect of simazine soil residues on com, wheat, barley, oats and soybeans ...... 37
The movement of simazine in soil in the fi e l d ...... 45
The movement of simazine and atrazine in soil in the laboratory...... 57
iii CONTENTS
Page
The effect of soil microorganisms on the breakdown of simazine . 61
The effect of simazine on the activity of soil microorganisms. . 66
SUMMARY AND CONCLUSIONS ...... 70
LITERATURE CITED...... 73
APPENDIX...... 81
AUTOBIOGRAPHY ...... 88
iv LIST OF TABLES
Table Page
1. Number and per cent reduction of annual broadleaf and grass weeds in corn treated pre-emergence with simazine on May 25, 1959. Counts were made on June 20, 1959, on 175 sq. ft. of each of 4 replicates. Values are the average of 4 replications...... 36
2. Yield of corn treated pre-emergence with simazine on May 25, 1959. Average of 4 replications ...... 37
3. Yield of corn, wheat, barley, oats and soybeans following corn treated pre-emergence with simazine. Values shown are the averages of four replications...... 38
4. Rainfall at University Farm, Columbus, O h i o ...... 38
5. Weight of first crop of oat seedlings grown in soil taken on October 15, 1959, from field plots treated with simazine on May 25, 1959. Values are grams of fresh weight and are the average of three replications .... 46
6. Weight of second crop of oat seedlings grown in soil taken on October 15, 1959, from field plots treated with simazine on May 25, 1959. Values are grams of fresh weight and are the average of three replications. . . . 47
7. Bioassay standards for weight of oat seedlings grown in soil freshly treated with simazine and randomized with soil taken from field plots on October 15, 1959. Values are grams of fresh weight and are the average of three replications ...... 47
8. Weight of first crop of oat seedlings grown in soil taken on May 12, 1960, from field plots treated with simazine on May 25, 1959. Values are grams of fresh weight and are the average of three replications...... 51
9. Weight of second crop of oat seedlings grown in soil taken on May 12, 1960, from field plots treated with simazine on May 25, 1959. Values are grams of fresh weight and are the average of three replications...... 52
v LIST OF TABLES Table Page
10. Bioassay standards for weight of oat seedlings grown in soil freshly treated with simazine and randomized with soil taken from field plots on May 12, 1960. Values are grams of fresh weight and are the average of three replications ...... 54
11. Weight of first crop of oat seedlings grown in soil taken on October 10, 1960, from field plots treated with simazine on May 25, 1959. Values are grams of fresh weight and are the average of three replications .... 54
12. Weight of second crop of oat seedlings grown in soil taken on October 10, 1960, from field plots treated with simazine on May 25, 1959. Values are grams of fresh weight and are the average of three replications .... 55
13. Bioassay standards for weight of oat seedlings grown in soil freshly treated with simazine and randomized with soil taken from field plots on October 10, 1960. Values are grams of fresh weight and are the average of three replications ...... 55
14. Weight of oat seedlings grown in two soil types treated with atrazine and simazine. Water was applied to the treated soil surfaces and the soil columns were sectioned into five one-inch levels. Values are grams fresh weight and are the average of three replications...... 58
15. Weight of oat seedlings grown in two soil types treated with atrazine and simazine. Four rates of water were applied to the treated soil surfaces. Values are grams fresh weight and are the average of three replications .... 59
16. Weight of oat seedlings grown in soil treated with atra zine and simazine. Four rates of water were applied to the treated soil surfaces and the soil columns were sectioned into five one-inch levels. Values are grams fresh weight and are the average of three replications . 62
17. Amount of carbon, evolved as carbon dioxide, from 100 grams of non-treated and simazine treated soil. Values are grams of carbon and are the average of four replications ...... 69
18. Analysis of variance for yield of corn treated pre emergence with simazine on May 25, 1959...... 81
19. Analysis of variance for yields of com, wheat, barley, oats and soybeans...... 82
vi LIST OF TABLES
Table Page
20. Analysis of variance for weight of first crop of oats grown in simazine treated soil taken from field plots on October 15, 1959...... 83
21. Analysis of variance for weight of second crop of oats grown in simazine treated soil taken from field plots on October 15, 1959...... 83
22. Analysis of variance for weight of first crop of oats grown in simazine treated soil taken from field plots on May 12, 1960...... 84
23. Analysis of variance for weight of second crop of oats grown in simazine treated soil taken from field plots on May 12, 1960...... 84
24. Analysis of variance for weight of first crop of oats grown in simazine treated soil taken from field plots on October 10, 1960...... 85
25. Analysis of variance for weight of second crop of oats grown in simazine treated soil taken from field plots on October 10, 1960...... 85
26. Analysis of variance for weight of oat seedlings grown on soil treated with atrazine and simazine which were leached with varying amounts of water applied to the soil surface ...... 86
27. Analysis of variance for the amount of carbon, evolved as carbon dioxide, from 100 grams of non-treated and sima zine treated soil...... 87
vii LIST OF FIGURES
Figure Page
1. Field plot design of experiment to determine the effects of simazine residue in soil on corn, wheat, barley, oats and soybeans. Simazine was applied at 0, 2, 4 and 8 pounds per acre on May 25, 1959, and the crops were planted on the indicated dates...... 26
2. The yield of com, wheat, barley, oats and soybeans following c o m treated pre-emergence with simazine. Yield expressed as per cent of c h e c k ...... 39
3. The growth of c o m in 1960 in plots receiving (left) no simazine and (right) 8 pounds of simazine per acre. The simazine was applied in May 1959 ...... 40
4. The growth of wheat in 1960 in plots receiving (top left) no simazine, (top right) 2 pounds of simazine per acre and (bottom) 8 pounds of simazine per acre. The sima zine was applied in May 1959 41
5. The growth of winter barley in 1960 in plots receiving (top left) no simazine, (top right) 2 pounds of sima zine per acre, (bottom left) 4 pounds of simazine per acre and (bottom right) 8 pounds of simazine per acre. The simazine was applied in May 1959 ...... 42
6. The growth of spring oats in 1960 in plots receiving (top left) no simazine, (top right) 2 pounds of sima zine per acre and (bottom) 8 pounds of simazine per acre. The simazine was applied in May 1959...... 43
7. The growth of soybeans in 1960 in plots receiving (top left) no simazine, (top right) 2 pounds of simazine per acre, (bottom left) 4 pounds of simazine per acre and (bottom right) 8 pounds of simazine per acre. The simazine was applied in May 1959 ...... 44
8. Reduction in weight of oat seedlings grown in simazine treated soil taken from field on October 15, 1959, and oats grown for bioassay standards. Percentages are based on fresh weight of three replications of two successive c r o p s ...... 48
viii LIST OF FIGURES
Figure Page
9. The growth of oats in soil taken from field plots on October 15, 1959, five months after the application of simazine. Top (left to right), soil of the 0 to 3, 3 to 6 and 6 to 9-inch levels from plots receiving 2 pounds of simazine per acre and the corresponding checks. Center (left to right), soil of the 0 to 3, 3 to 6 and 6 to 9-inch levels from plots receiving 4 pounds of simazine per acre and the corresponding checks. Bottom (left to^right), soil of the 0 to 3, 3 to 6 and 6 to 9-inch levels from plots receiving 8 pounds of simazine per acre and the corresponding c h e c k s ...... 49
10. Reduction in weight of oat seedlings grown in simazine treated soil taken from field on May 12, 1960, and oats grown for bioassay standards. Percentages are based on fresh weight of three replications of two successive crops ...... 53
11. Reduction in weight of oat seedlings grown in simazine treated soil taken from field on October 10, 1960, and oats grown for bioassay standards. Percentages are based on fresh weight of three replications of two successive crops ...... 56
12. The growth of oats in clay soil treated with atrazine (top row) and simazine (bottom row). Duplicate pots from left to right in each picture are 0 to 1, 1 to 2, 2 to 3, 3 to 4, 4 to 5-inch soil levels and the corresponding check. The soil in the pictures from left to right received no water, 1 inch, 2 inches and 4 inches of water after the herbicides were applied...... 60
13. Relative weight of oat seedlings grown in two soil types treated with atrazine and simazine. Four rates of water were applied to the treated soil surfaces and the soil columns were sectioned into one-inch layers. Values are expressed as per cent of check...... 64
14. The radioactivity of BaC0 3 , formed from CO 2 evolved from soil treated with carbon^-labeled simazine, and the relative amounts of simazine decomposition, measured at weekly intervals. Values are expressed in counts per minute of beta ray emissions and per cent maximum decomposition of simazine and are the average of four replications ...... 65
ix LIST OF FIGURES
Figure Page
15. Weekly accumulation of carbon, evolved as CO2 , from 100 grams of non-treated and simazine treated soil. Values are the average of four replications...... 67
16. Total accumulation of carbon, evolved as CO2 , from 100 grams of non-treated and simazine treated soil. Values are the average of four replications...... 68
x INTRODUCTION
Effective and economical weed control is essential for the profit able production of crops. Broadleaf and grass weeds are highly compet itive with crops for moisture, nutrients and sometimes light. Mechanical methods of controlling weeds are at times adequate but often they are labor consuming, expensive, ineffective and injurious to the crop.
Since the introduction of 2,4-D (2,4-dichlorophenoxyacetic acid) as a herbicide, about two decades ago, hundreds of organic compounds have been tested for herbicidal properties. Simazine [2-chloro-4,6-bis
(ethylamino)-j^-triazine] was introduced into the United States in 1956.
It controls most annual species of grass and broadleaf weeds; however, corn plants are very tolerant to the compound (8). The herbicide most used on corn before the introduction of simazine was 2,4-D which was very effective on annual broadleaf weeds but was relatively ineffective on the grasses. In fact, the weed problem in many arqas of the c o m belt changed from one of broadleaf weeds to one of grasses. This was due to the continued use of 2,4-D which eliminated the broadleaf weed competition and consequently less cultural practices were used, allowing the grasses to flourish. Growth-regulating compounds, such as 2,4-D, under certain moisture and temperature conditions, have caused injury to c o m plants. Simazine is non-injurious to c o m plants at rates in excess of the minimum amount required for effective weed control.
1 Many herbicides, including simazine, must act through the medium of the soil and be absorbed by the roots of the susceptible plants (8,
28, 29, 71, 76, 82). It is important that the beneficial microbial pro cesses not be adversely affected by herbicides applied to the soil.
In a crop rotation it is important that a herbicide used on a crop will not remain in the soil and cause damage to subsequent suscep tible crops.
The proposed objectives of this study were (1) to determine the effectiveness of simazine applied as a pre-emergence spray to control annual weeds in corn, (2) to determine the effects of simazine residues on crops subsequent to c o m which received pre-emergence treatments of simazine, (3) to study the movement of simazine and atrazine (2-chloro-
4-ethylamino-6-isopropylamino-j5-triazine) in soil, (4) to determine the effect of soil microorganisms on the metabolism of simazine and (5) to determine the effect of simazine on the activity of soil microorganisms REVIEW OF LITERATURE
The effectiveness of s-fmazine as an herbicide when applied to corn
Simazine was synthesized in the J. R. Geigy Laboratory, Basle,
Switzerland, by Gysin and Knusli (77). It was first released for exper imental use in the United States in 1956. From the beginning this triazine compound looked extremely promising as a pre-emergence herbicide when applied in corn. During the early part of 1958 the United States
Food and Drug Administration and United States Department of Agriculture accepted the label claims for the use of simazine on several different ornamental and nursery plants and for use in field, sweet, seed and silage c o m (8).
Bondarenko et^ _al_. (15, 16) reported that 2, 3 and 4 pounds per acre of simazine applied pre-emergence in field c o m grown on silty clay loam soil reduced the weed population 90 per cent or more at three loca tions in Ohio in 1958 and 1960. The one pound per acre rate of simazine reduced the weed population 90 per cent or more at two of the three locations. They reported that granular and spray applications of sima zine were equal in effectiveness when applied at the same rates and that no injury to the c o m was detected. In comparing the effectiveness of simazine applied pre-emergence in field c o m as a spray and as granules,
Agundis and Bondarenko (1) found that both formulations applied at 2 and 4 pounds per acre resulted in 80 to 100 per cent weed control with no significant difference between formulations. Neither formulations nor rates caused any injury symptoms or yield reduction of the corn.
However, under high rainfall conditions, simazine applied as granules resulted in better weed control than an equal amount of the wettable powder applied as a spray (35). The granular material at 1 and 2 pounds per acre resulted in 80 and 95 per cent weed control while the 80 per cent wettable powder reduced the weed population 50 and 75 per cent.
Stroube and Bondarenko (86) reported that simazine applied pre-emergence in field corn in 1959, at rates of 1 and 2 pounds per acre, resulted in excellent weed control at one location but was unsatisfactory at another.
The soil at the latter test had a high clay content and there was no rainfall for a considerable period of time following application. There was no evidence of injury to the com.
From three years of testing in Kentucky, reduction in weed popula tions of 92 to 100 per cent was obtained where simazine was applied pre-emergence in field corn at rates of 1 to 3 pounds per acre (38, 39,
40). No injury symptoms of the corn were observed during these tests.
Three and six pounds of simazine per acre, applied pre-emergence in field corn, reduced the weed population 86 and 92 per cent, respec tively, with no injury to the corn (17). Williams and Lee (96) received excellent weed control with simazine at a rate of 3 pounds per acre when applied pre-emergence in field corn on silt loam soil, with no injury to the corn. One of the first to test simazine in the field was
Shear (80). In 1957, he secured 63 to 93 per cent weed control where he applied simazine pre-emergence at 1 to 3 pounds per acre in field corn. In 1958, he reported 83 and 93 per cent weed control with simazine at rates of 1 and 2 pounds per acre and observed no injury symptoms in the corn.
Complete control of annual broadleaf and grass weeds resulted throughout the growing season where simazine was applied at 2 pounds per acre in field c o m on a silt loam soil (56). Simazine applied pre emergence in c o m at 4 pounds per acre completely eliminated all weeds according to Zinter e£ a^l. (100). At 2 pounds per acre 100 per cent control of the broadleaf weeds, 98 per cent control of foxtail grass
(Setaria spp.) and 75 per cent control of wild oats (Avena fatua) resulted. Friesen (41) stated that simazine applied pre-emergence in field c o m at rates as low as 1 pound per acre resulted in good control of all weeds except wild oats, and it required 2 or more pounds per acre for effective control of that specie. He reported that no injury to corn was observed. Granular simazine, applied pre-emergence to c o m at rates of 3 and 4 pounds per acre, resulted in 85 and 95 per cent control of wild oats, according to Dercheid (33). When Anderson (5) applied simazine pre-emergence in corn at a rate of 2 pounds per acre, 80 per cent control of broadleaf and grass weeds was obtained. At 3 pounds per acre, simazine reduced the population of broadleaf weeds 100 per cent and grass weeds 84 per cent and at 4 pounds per acre 100 per cent of the broadleaf weeds and 89 per cent of the grass weeds were eliminated.
Simazine provided excellent pre-emergence control of annual broad leaf and grass weeds throughout the growing season in Florida (70). To insure this degree of control in Florida soils the rates necessary were
1 pound per acre on sandy soils, 1% pounds on coastal plains sands con taining organic matter, 2 to 2% pounds on clay soils, 3 pounds on higher organic matter soils and 4 pounds on muck soils. Soils high in organic matter and/or clay content caused reduced simazine phytotoxicity as com pared to soils low in these components (20). Three to four pounds of simazine per acre applied pre-emergence gave fair to good weed control
in muck soil while lower rates resulted in poor weed control (35, 40).
Simazine at rates of 2 and 2% pounds per acre applied pre-emergence
in several inbred lines of field corn caused no injury to the corn
(57, 73).
Simazine at 2 to 3 pounds per acre applied pre-emergence resulted
in good to excellent weed control in sweet corn with no injury to the corn (71, 79). Danielson (27) reported that simazine applied pre emergence at rates of 1, 2 and 4 pounds per acre resulted in good to excellent weed control with no effect on several varieties of sweet corn; however, 8 pounds per acre caused some differential response to eight varieties of sweet corn. No delay of germination or reduction in stand of ninety varieties of sweet corn occurred when simazine was applied pre-emergence at 5 and 10 pounds per acre, according to Chaplin and Alban (24). Seventeen of the ninety varieties exhibited significant dwarfing at the 10 pounds per acre rate. The maturity of five varieties was delayed two to four days at the heavier rate of application and two varieties revealed some indications of delayed maturity at the 5 pounds per acre rate. Three varieties exhibited a significant reduction in number of marketable ears and ear weight when treated with 10 pounds of
simazine per acre and the total weight and number of harvested ears of
one variety was significantly reduced at the 5 pounds per acre rate. In a greenhouse study the stunting of c o m occurred only after it was grown for a prolonged period in a highly concentrated solution of simazine
(29). Increased soil temperature, within limits, increased simazine toxicity to corn (20).
Barley plants, which are naturally susceptible to simazine, treated with simazine and subsequently supplied with a source of glucose, remained alive while those not supplied glucose died (61). Simazine reduced the photochemical activity (Hill reaction) of isolated barley chloroplasts by 50 per cent at a 4.6 X 10“^M solution. This indicated that simazine killed plants by interfering with photosynthesis. Isolated chloroplasts of corn reacted similar to those of barley so the mechanisms which control selectivity was assumed to act before the herbicide reached the chloroplasts.
Corn tolerated rates of simazine in excess of the amounts required to kill other plants due to a decomposition of simazine by enzyme action within the plant shortly after absorption from the soil (76, 77). A residue analysis of various parts of the corn plant indicated the absence of simazine. Montgomery and Freed (59, 60) conducted experiments with corn plants grown in a solution containing simazine with the carbon atoms in the triazine being isotope carbon-14 (radioactive material).
They found that the corn plants evolved C ^ 0 2 which indicated that some of the simazine molecules were completely metabolized in the corn plant.
By using expressed sap of corn plants grown as described above, they found by the use of paper chromatography that most of the radioactive material remaining in the corn plant was broken down into simpler com pounds containing the atoms. Ragab and McCollum (68) found that C^02 evolved from c o m and cucumber plants which were treated with C^-labeled simazine. In fact, cucumber plants, a relative susceptible species, decomposed simazine at a more rapid rate than did c o m plants. They also found that the cucum ber plants absorbed simazine more rapidly than corn plants which may partially account for the selective toxicity. Similarly, Davis ejt al.
(28, 29) found that C^ 0 2 was evolved by corn, cotton and cucumber which were grown in C^-labeled simazine solutions. There seemed to be no correlation with the amount of C ^ 0 2 evolved and the relative suscepti bility of the test plants.
The resistance of c o m was due to a system in corn tissues which metabolized simazine to a biologically inactive product according to
Roth (75). Expressed maize juice was able to decompose simazine while
that of wheat decomposed little or no simazine. This conflicts somewhat with the finding of Ragab and McCollum (68) and Davis et al. (28, 29).
The movement and persistence of herbicides in soil
There are many factors which affect the movement and persistence of herbicides in soils. Especially with herbicides applied to the soil, persistence and leachability are extremely important. Once applied to
soils, herbicides may be decomposed by microorganisms, decomposed chem
ically or photochemically, leached out of the root zone, adsorbed on
soil colloids, volatilized or absorbed by plants (3, 63, 72, 77, 83).
Factors which may determine the importance of these methods of inactiva
tion are the nature of the herbicide, the composition of the soil and
environmental conditions. The physical properties of different herbicides vary greatly.
Some are practically non-soluble and non-volatile while others are extremely soluble and volatile.
Soils vary in texture, chemical composition, organic matter, pH, moisture and temperature. Many complex and ever-changing processes occur continuously in most soils. Soils are composed of mineral matter, organic matter, water and air. The mineral fraction varies in amounts of sand, silt and clay and in types of clay minerals. The base satura
tion and adsorptive capacity of the clay minerals vary. The organic matter fraction consists of decaying plant and animal residues which is
important in determining the microbial population of a soil.
Soil moisture and temperature may fluctuate rapidly in any one
soil while the aforementioned factors are slower to change. The soil atmosphere is composed of oxygen, carbon dioxide, nitrogen and several
other gases. The composition of the soil atmosphere varies, particularly
the oxygen and carbon dioxide contents. The extreme complexity and var
iation of soil systems make the study of the movement and persistence of herbicides complicated.
With many herbicides, decomposition by microorganisms appears to be the single most important factor in their disappearance but with
others leaching or adsorption on soil colloids seem to be more important.
Frequently a combination of factors apparently is responsible for the
inactivation of herbicides.
Leaching of herbicides was affected by the solubility of the
herbicide, the amount and intensity of rainfall, the soil texture and
the adsorptive capacity of the soil as influenced by organic matter 10
and amounts and types of clay minerals (3, 25, 30, 46, 48, 63, 67, 72,
74, 81, 83, 84, 93, 94). At least two steps are involved in the movement
of a herbicide downward in soil. These steps are the entrance of the
herbicide into solution and the adsorption of the herbicide to the soil
particle. Entrance into solution could occur from solid particles of
the herbicide or from colloidal particles with adsorbed herbicide mole
cules (93, 94).
Some workers contended that solubility of a herbicide is not the
explanation of a relatively low rate of leaching because even the more
insoluble compounds are within the capacity of natural or applied rain
fall. One inch of rain on an acre has the capacity to dissolve one
pound of simazine which is one of the least soluble herbicides (5 ppm.
in water). Little difference was found between monuron [3-(j3-chloro-
phenyl)-l,1-dimethylurea] and simazine with regard to downward movement
even though monuron is forty times more soluble in water than simazine
(81). Upchurch and Pierce (94) suggested that solubility was involved
in monuron movement in soils especially when heavy rates were applied.
When the rate of application of monuron was increased from 32 to 64 to
128 to 256 pounds per acre, the percentage retention in the 0 to 2-inch
soil level increased when four inches of simulated rainfall was applied.
The principal factors affecting leaching of 2,4-D were soil char
acteristics, solubility and fixation of the chemical and the total
amount and intensity of rainfall, according to Robinson (72), who found
that 80 per cent of an amine salt of 2,4-D was leached through a four-
inch column of silt loam soil by three surface inches of water while the
greatest concentration of a long-chain ester of 2,4-D was adsorbed at 11 the surface. Various clay minerals adsorbed different amounts of each form of 2,4-D. Similarly adsorption of the esters of 2,4-D was found to be greater than that of the amine salt and adsorption was greater in high organic matter soils and mucks than in low organic matter soils
(46, 63, 67). By adding organic matter to soils, Robinson (72) increased the affinity of the soil for a long-chain ester of 2,4-D but not for an amine salt formulation. The mobility of dalapon (2,2-dichloropropionic acid) in soil was reduced when manure was added but was increased with the addition of sand (48). Similar to this were the findings of
Sherburne and Freed (84) who reported that activated charcoal, sawdust, straw, organic matter and clay increased the amount of monuron adsorbed and that sandy soil had low affinity for monuron.
Sodium chlorate penetrated to a lower level in columns of sandy soil than in soil with a high clay content (74). DNBP (4,6-dinitro- o-sec-butylphenol) penetrated deeper and in larger quantities in coarse, sandy soil than in finer soils (30). The water soluble formulation of this herbicide leached more readily with high rates than low rates of water. Upchurch and Pierce (93) confirmed the latter point when testing the properties of monuron. They reported that the greater the amount of rainfall, the greater the movement of monuron. They also tested the intensity and frequency of simulated rainfall and concluded that of the
three variables studied, the amount of rainfall would be most directly correlated with the distribution of herbicides in soil profiles under field conditions. Diuron [3-(3,4-dichlorophenyl)-l,1-dimethylurea], which is similar in structure and herbicidal properties to monuron, 12 was leached more rapidly under irrigation than natural rainfall but not
to a deeper level in the soil (95).
TCA (trichloroacetic acid) and dalapon leached rapidly from sandy,
silt loam and muck soils while IPC (isopropyl-N-phenylcarbamate),
CIPC [isopropyl N-(3-chlorophenyl) carbamate] and monuron were resistant
to leaching in all three soils (63, 67).
The herbicidal activity of simazine in soil was apparently reduced
by adsorption on soil colloids, leaching and by cultural practices (77),
but according to Montgomery and Freed (58), leaching was a relatively
unimportant factor. The latter applied C-^-labeled simazine, at a rate
of 12 pounds per acre, to the surface of soil columns and applied 12
inches of water within a 3-day period. Some simazine penetrated to a
depth of seven inches but the maximum concentration was at the 0 to
1-inch soil level.
Many workers studying herbicide loss from soils reported a more
rapid inactivation in soils under conditions favorable for reproduction
and growth of microorganisms (3, 7, 18, 26, 46, 48, 54, 83, 87, 92, 99).
The rate of inactivation of 2,4-D was found by Brown and Mitchell
(18) to be most rapid at a moisture content of 30 to 70 per cent and
toxic effects persisted for prolonged periods of low temperature. With
the addition of manure the rate of inactivation was increased but was
decreased when the soil was autoclaved. However, Akamine reported that
the addition of organic matter did not affect the disappearance of 2,4-D
toxicity. Ten pounds of 2,4-D per acre disappeared from soil in 2 to 14
weeks, depending on the soil temperature and pH values. The persistence 13 of 2,4-D increased with aridity and low temperatures and the application rate seemed to be unrelated to persistence (31, 46).
The rate of disappearance of 2,4-D was increased when it was applied to soil which had been previously treated with 2,4-D (3, 65,
66). This indicated that the soil microorganisms either adapted to the environment containing 2,4-D or that the microbes, capable of metabo
lizing 2,4-D, increased as the result of 2,4-D having been applied pre viously. The microbial breakdown of 2,4-D, after an initial lag period,
followed a curve resembling that of a reaction following first order kinetics (6).
Most organic herbicides can be used as a source of food by certain bacteria and fungi according to Anderson (4). He found that 2,4-D and
dalapon were readily attacked by microbes and disappeared rapidly from
soils. Holstun (48) and Theigs (92) agreed that the disappearance of
dalapon was primarily a function of microbial decomposition.
Soil microorganisms influenced the disappearance of 2,4,5-T
(2,4,5-trichlorophenoxyacetic acid) less than equal amounts of 2,4-D
(4, 31, 83). Silvex [2-(2,4,5-trichlorophenoxy) propionic acid] reacted
similarly to 2,4,5-T when applied to soil (83).
In a study of microbial breakdown of monuron, Hill jet ad. (47)
found that in contrast to the rapid rate of breakdown of 2,4-D, a steady
state of decomposition of the urea product was obtained which indicated
that it was much less readily attacked by microorganisms and persisted
for substantial longer periods. The toxicity of monuron persisted longer
at 10°C. than at 28 or 45°C. (54). The toxicity also persisted longer in
air dry soil than in medium moist or saturated soil. There was a definite 14
correlation with the factors favoring increased microbial action and the
disappearance of monuron in soil. Sheets and Danielson (83) reported
that repeat applications of the phenylureas (monuron included) and the js-triazines (simazine included) were unlike 2,4-D and did not disappear
any more rapidly than the initial applications. They theorized that with
these two compounds the action of soil microorganisms was passive in that
organisms utilized them but not selectively or preferentially.
In soil treated with C^-labeled amitrole (3-amino-l,2,4-triazole),
Bondarenko (12, 13) found that C^02 evolved from soil within 24 hours
indicating decomposition of the material. The rate of C^02 evolution
increased until the thirteenth day following treatment and then decreased
rapidly until the forty-second day. After that it gradually decreased
until the 240th day which was the termination of the experiment. Sund
(87) reported that the rate of decomposition of amitrole was different
in various types of soil and that his data indicated the ultimate break
down was due to microbiological attack. Somewhat contrary to this,
Newman and Downing (63) reported that it appeared doubtful that micro
organisms played an important role in the disappearance of amitrole. The
rate of breakdown of amitrole, IPC and CIPC at temperatures of 15 and
29°C indicated that the decomposition process was a first order reaction
and that disappearance was greater at the higher temperature (21).
Similar findings relative to IPC and CIPC were reported by Newman and
Downing (63), who found that in studies with radioactively labeled IPC
and CIPC, microbial action was important in the loss of these compounds
from a silty loam soil. Conversely, Newman et al. (64) reported that
temperature seemed to have little effect on IPC decomposition. 15
PCP (pentochlorophenol) decomposed more rapidly in an organic soil as opposed to a mineral soil. Rate of decomposition was greatest at a moisture content near the moisture equivalent and at a temperature near optimum for microbial activity (99).
Sagab and McCollum (6 8 ) applied C-^-labeled simazine to autoclaved and non-autoclaved soil and trapped the evolved C02» During the first
91 hours, the rate of decomposition of C-^-simazine into C^ 0 2 and other degradient products was very high in the non-autoelaved soil while vir tually no C ^ 0 2 evolved from the sterile soil.
Microorganisms, which were capable of development in an environment with an extremely high level of simazine (2 to 5 per cent)^ were isolated by Guillemat (42). These organisms were studied on gelation low in car bon and nitrogen and with and without a supply of simazine. From the results of this study he made the following statements with some reser vations: (1 ) practically no development was obtained on a medium void of carbon and nitrogen, (2) the carbon of the simazine was rarely uti lized by the organisms, (3) the organisms were capable of utilizing the nitrogen of simazine and (4) the utilization of simazine was much greater when there was a large supply of available carbon in the environment.
The latter statement is particularly interesting because it is an explan ation of why soils high in organic matter decompose simazine more rapidly than soils of low organic matter.
Conditions favorable for rapid microorganism growth also favored rapid detoxification of soil treated with simazine and atrazine. These compounds at a rate of two pounds per acre lost their toxicity after 16 eight weeks when the soil was moist and warm but in dry soil enough residues remained after twelve months to cause injury to oats (89).
Simazine has been widely tested as a pre-emergence selective herb icide in corn. Rates of one to four pounds per acre generally controlled all species of annual weeds for six weeks or more. Although corn is tolerant to this herbicide practically all other crops are highly sus ceptible to it. It is very important to know the effect of simazine residues in the soil on the production of subsequent crops.
Simazine and atrazine were applied at rates of 2, 6 and 12 pounds per acre in silt loam soil in November in Minnesota. Reduction in stands of flax, wheat, oats, soybeans and broadleaf and grass weeds occurred when seeded six months after application at all rates except soybeans at the two-pound rate of simazine. The phytotoxicity of atrazine was greater than simazine in every comparison (10). In Missouri, the yields of wheat were reduced 32, 92 and 99 per cent when seeded in the fall following corn which had been treated with simazine at rates of 2, 4 and
8 pounds per acre. The yields of oats seeded the following spring were reduced 5, 95 and 99 per cent at the/rates of 2, 4 and 8 pounds per acre.
Soybeans seeded twelve months after simazine application showed some injury symptoms at the 2 and 4 pound per acre rates but with no reduction in yields. At the 8 -pound rate, the yield was reduced 71 per cent. (37).
In Ohio, soybean stands were reduced 50, 100 and 100 per cent when planted 36 days after the application of simazine at rates of 4, 8 and
12 pounds per acre. Simazine, applied at rates of 2, 4, 8 and 12 pounds per acre in October, reduced the stand of soybeans planted the following
May by 0, 40, 100 and 100 per cent, respectively (14). 17
Wheat and oats, seeded a year after the application of 1, 2 and 4
pounds of simazine per acre, were not injured according to Bayer (9).
Oat yields in Minnesota were not reduced when seeded one year after
simazine was applied in bands at rates of 2, 4 and 6 pounds per acre
but where applied overall at 4 and 6 pounds per acre, the yields were
significantly reduced. At the 6 -pound per acre rate applied overall,
oat yields were reduced 50 per cent when seeded two years after applica
tion (11). Simazine applied in June at 1 and 2 pounds per acre caused
no injury to oats seeded 13 months later but were slightly chlorotic at
a 3-pound rate (8 8 ). Buchholtz (19) applied simazine and atrazine at
rates of 1, 2 and 4 pounds per acre in May and seeded oats and alfalfa
the following April. Simazine at 1 and 2 pounds per acre and atrazine
at all rates did not significantly reduce oat yields. Simazine at 4
pounds per acre reduced the yield of oats in one test but not another.
Alfalfa stands were not reduced in any instance.
In a greenhouse test, Chadwick (22) reported that stands of oats were reduced 94, 48 and 5 per cent when seeded 4, 8 and 12 weeks after
the application of 1% pounds of simazine per acre. At a rate of 3
pounds per acre, oat stands were reduced 100, 90 and 38 per cent when
seeded 4, 8 and 12 weeks after application.
Scudder (78) studied the effect of simazine residues in Florida
soils on several vegetables. In peat, the vegetable crops were not
injured when seeded 8 months after the application of 2, 4 and 6 pounds
of simazine per acre. Higher rates caused crop injury. Seeded 18
months after application, no injury to the vegetables occurred at rates
of 2, 4, 8 , 16 and 32 pounds per acre. In sandy soil, he found that 18 oats and the vegetable crops grew normally when seeded one year after soil incorporation of 1, 2, 4 and 8 pounds of simazine per acre. A 16- pound rate caused crop injury. The same crops grew normally when seeded in sandy soil one year following the surface application of 1, 2 and 4 pounds of simazine per acre but were injured at rates of 8 and 16 pounds per acre.
The effect of herbicides on soil microorganisms
It is important that herbicides applied to soil not have any detri mental effect on beneficial soil microorganisms or their vital processes.
The variation of effects of existing herbicides on soil organisms already recorded makes it imperative to study each new and untested herbicide and its relation to soil microorganisms. If a compound had any retarding or stimulating influence on microbes, it would be detected in carbon dioxide evolution during soil respiration experiments. Such a measure would be purely quantitative and would in no way relate information on individual species of soil microorganisms.
Most of the early studies conducted on effects of herbicides on soil microorganisms were concerned with 2,4-D and related phenoxyacetic herbicides. Fortunately, the majority of herbicides appear to do no per manent harm to the soil microflora when applied at rates even somewhat in excess of the minimum amount required for the control of weeds.
There is general agreement that 2,4-D and related compounds at fates used for weed control have no adverse effects on the total number of microorganisms in the soil (3, 4, 36, 43, 49, 50, 51, 62, 63, 85, 90,
91). 19
Concentrations of 2,4-D ranging from 0.5 to 500 ppm. had very
little influence on the total microbial population in a sandy soil; how ever, nitrite and nitrate-forming organisms were inhibited at a concen
tration of 100 ppm. but recovered in 10 to 40 days (85). At rates from
8 to 32 pounds of 2,4-D per acre markedly reduced the nitrate accumula
tion in the soil (62, 91). A rate of 2 pounds of 2,4-D per acre had no
influence on the nitrate accumulation. The total microbial activity as measured by CO2 evolution was significantly increased by 2,4-D at the
32 pounds per acre rate but not at 2 and 8 pounds (91). Up to 25 pounds
of 2,4-D per acre had no unfavorable effects on nitrate formation in a
soil to which no nitrogen had been added but when urea and sodium
nitrate were added, 15 pounds of 2,4-D inhibited nitrate formation tem
porarily (49). Koike and Gainey (50) reported that 2 pounds of 2,4-D
per acre applied to sandy or silt loam soils did not reduce the total
nitrate accumulation. Higher rates temporarily reduced the nitrates but
total accumulation equaled the untreated soil after 8 to 16 weeks.
Application rates of 2,4-D and 2,4,5-T at several times the recom
mended rates had no effect on the CO 2 evolution of treated soils. It
had to be applied at about 100 times the recommended rate before the
activity of soil microbes was altered sufficiently to detect (4, 51).
The respiration of Azotobacter species was inhibited by 2,4-D concentra
tions of 10,000 ppm. and the organisms were more sensitive to 2,4,5-T
than to 2,4-D (55).
Soil microorganisms were inhibited more by 2,4-D and other phenoxy-
acetic compounds under acid than neutral or alkaline conditions (62, 63). 20
There was considerable variation in the susceptibility of different soil microorganisms to a particular herbicide according to Aldrich (3) and Newman and Downing (63). In fact, Reid (69) stated that in many cases microorganisms adapted to the environment and utilized the herbi cide as food. Aerobic organisms were inhibited in activity at a lesser
1 concentration of 2,4-D than were anaerobic or facultative anaerobic organisms (63, 98).
Alexander (4) reported that amitrole did not alter the activity of soil microbes until levels of about 100 times the recommended rates were applied. Likewise, Bondarenko (13) found that amitrole applied at rates of 6 and 12 pounds per acre failed to influence the amount of CO 2 evolved from soils.
Rates as low as 6 pounds per acre of CIPC and CDEA (2-chloro-lJ, N- diethylacetamide) and 24 pounds of CDEC (2-chloroallyl diethyldithio- carbamate) significantly increased the total CO2 evolution from a silty clay loam during a 33 day study but reduced nitrate accumulation. A rate of 96 pounds per acre of CDEA essentially prohibited nitrate accumulation
(43, 91).
Dalapon at concentrations from 50 to 150 ppm. increased the oxygen uptake of soil microorganisms. At concentrations up to 600 ppm. oxygen uptake was slightly inhibited (43). Worsham and Giddens (97) applied dalapon at rates of 17, 34 and 68 pounds per acre to sandy soil in the greenhouse and found little or no effect on the overall microbial population.
Sodium chlorate at concentrations of 250 to 500 ppm. decreased the microorganism content of soil 50 per cent one week after application. 21
Similar concentrations greatly inhibited the nitrification process
(44, 85).
In a study of the effect of simazine on microorganisms, Guillemat
(42) of France found that six months after treatment, the microflora of soils receiving 6 kilograms of simazine per hectare (approximately 5.3 pounds per acre) had not been altered as to total population or variety of species. Where simazine was applied at rates of approximately 26, 52,
132 and 264 pounds per acre, the analysis of the microflora revealed no serious modifications of the microbiological balance of the treated soil.
In another study of the effects of simazine on microorganisms, Chandra et al. (23) measured the CO 2 evolution from nine Oregon soils to which simazine had been applied at concentrations of 5 and 100 ppm. Simazine decreased the rate of CO2 evolution for 28 days but after that no effect was noted. There was no consistent pattern as to the influence of con centration of simazine or to the organic matter and clay content of the soils on CO2 evolution. EXPERIMENTAL MATERIALS AND METHODS
Properties and source of herbicides
Simazine [2-chloro-4,6 -bis(ethylamino)-s-triazine] is a hetero cyclic compound with the following structural formula:
Cl
N N ? II If C 2H 5 -N-C C - N - C 2H 5 NN/
2-chloro-4,6 -bis(ethylamino)-s-triazine
This herbicide has a molecular weight of 201.6 and is a white crys talline material with a melting point of 225°C. The solubility of tech nical simazine in the following solvents is: petroleum ether - 2 ppm., water - 5 ppm., methyl alcohol - 400 ppm. and chloroform - 900 ppm.
Simazine has a low mammalian toxicity. The acute oral LD^q to rats and mice is in excess of 5000 mg/kg body weight.
At the beginning of the experiment (1959), simazine was formulated into a 50 per cent wettable powder. At the time of this writing (1961), it is formulated into an 80 per cent wettable powder and on attaclay granules at a 4 per cent concentration.
The C^-labeled simazine used in this study had carbon-14 atoms uniformly distributed at the 2, 4 and 6 positions of the triazine ring.
The specific activity of the material was 1.11 millicuries per millimole with a half-life of approximately 5,600 years.
22 s
23
Atrazine (2 -chloro-4 -ethylamino-6 -isopropylamino-j3-triazine) is a heterocyclic compound with the following structural formula:
Cl I
H H ii 7 H g j^C - i - C ^ C - N - C2H5
2-chloro-4-ethy lamino-6-isopropylamino-js-triazine
This herbicide has a molecular weight of 215.6 and is a white crys talline material with a melting point between 173 and 175°C. The solu bility of atrazine is considerably higher than simazine but when compared to most herbicides it is relatively insoluble in water. The solubility of atrazine in the following solvents is: water - 70 ppm., ethyl ether -
12,000 ppm., methyl alcohol - 18,000 ppm. and chloroform - 52,000 ppm.
The acute oral LD5Q of atrazine to rats and mice is 3080 mg/kg body weight and 1750 mg/kg body weight, respectively.
Atrazine is formulated into an 80 per cent wettable powder and in granules of ammonium sulfate at a concentration of 20 per cent.
The atrazine and unlabeled simazine were supplied by the Geigy
Chemical Corporation, Ardsley, New York. The C^-labeled simazine was prepared by Tracerlab, Inc., Boston, Massachusetts and financed by the
Geigy Chemical Corporation.
The effect of simazine on weed population and corn yield
A field experiment was designed to determine the effect of differ ent rates of simazine on weed control and c o m yield. This same area was used to determine the effect of soil residues of simazine on field 24
crops and to study the movement of simazine in soil. The field experi ment was conducted on plot 2540 on The Ohio State University Agronomy
Farm, Columbus, Ohio. The size of the area was 200 by 210 feet and was
level to a one per cent slope. The soil type was Miami silt loam con
taining 17.1 per cent sand, 45.4 per cent silt and 37.5 per cent clay.
The organic matter content of the soil was 4.5 per cent and the pH was
6.0 .
The experimental area was in small grain in 1958. The stubble and
500 pounds of 12-12-12 fertilizer per acre were plowed under in March
1959. The area was fitted and planted to Ohio Certified W-64 hybrid
c o m in 42-inch rows on May 25, 1959. One hundred fifty pounds of
1 2 - 1 2 - 1 2 fertilizer per acre were applied in the row at the time of
planting. Immediately after planting, simazine was applied at rates of
0, 2, 4 and 8 pounds of active ingredient per acre in a randomized com
plete block design with four replications. Each plot was 52.5 feet
(15 rows) by 50 feet. The simazine was formulated as a 50 per cent wet
table powder and was applied in water at a rate of 80 gallons per acre.
Application was made with a tractor mounted power sprayer equipped with
a boom containing Teejet No. 8004 nozzles at 20-inch intervals and
adjusted to a height of 20 to 22 inches above the soil. By maintaining
a tractor speed of three miles per hour and a pressure of forty pounds
per square inch, the spray solution was discharged at a rate of forty
gallons per acre. Each plot was sprayed twice to insure more uniform
coverage and to eliminate any possible plugging of nozzles with the
higher rate of simazine. 25
The weed population was determined by counting the number of broad-
leaf and grass weeds in a ten-foot length between two rows of corn. Five
such countings were made for each plot and the number of total broadleaf and total grass weeds per fifty feet of row was recorded for each plot
on June 20, 1959. The rows and areas between rows were selected at ran
dom within the plots.
To eliminate any differences in corn yields due to weed competition,
the c o m was cultivated twice and hoed after the weed population was determined.
To determine the c o m yield, an area 28 feet (8 rows) wide and 30
feet long was hand harvested and weighed from each plot on October 2,
1959. Moisture percentages were determined on a sample from each sub
plot by a Steinlite Electronic Moisture Tester and yields were calculated
on the basis of 15.5 per cent moisture.
The effect of simazine soil residues on com, wheat, barley, oats and soybeans
The experimental area for this study was the same as that used in
the previous study and the simazine residues were from the simazine which was applied on May 25, 1959. After the c o m was harvested, the stalks were shredded and all plots disked. Each 50 feet by 52.5 feet plot was
divided into five sub-plots and a test crop was planted in each sub-plot
(Figure 1).
Dual wheat was seeded at a rate of six pecks per acre on October
15, 1959. Dayton barley was seeded on the same date at a rate of two
bushels per acre. Clintland oats were seeded at a rate of two bushels
per acre on April 18, 1960. The sub-plots seeded to oats were disked REPLICATIONS
I II______III______IIII
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III 1 II II . t._.....i ' } , ■ 210 feet
Figure 1. Field plot design of experiment to determine the effects of simazine residue in soil on corn, wheat, barley, oats and soybeans Simazine was applied at 0, 2, 4 and 8 pounds per acre on May 25, 1959 and the crops were planted on the indicated dates. 27 prior to seeding. On April 18, 1960, an alfalfa-bromegrass mixture was interseeded in the oat sub-plots, a red clover-timothy mixture in the wheat sub-plots and a sweet clover-orchardgrass mixture in the barley sub-plots. The sub-plots for corn and soybeans were plowed in April 1960.
O After seed-bed preparation, W-64 hybrid c o m was planted on June 17,
1960, and Harosoy soybeans were planted at a rate of one bushel per acre on June 20, 1960.
The small grains were seeded with a grain drill containing nine disks seven inches apart. Three hundred pounds of 5-20-20 fertilizer were applied per acre when the grains were seeded. The c o m and soybeans were planted in 42-inch rows with a tractor mounted planter. Five hun dred pounds of 12-1 2 - 1 2 fertilizer per acre were disked in the c o m sub plots during the seed-bed preparation and 150 pounds per acre were applied at the time of planting. Two hundred pounds of 0-20-20 fertili zer were applied per acre when the soybeans were planted. To eliminate weeds, the c o m and soybeans sub-plots were cultivated and hoed as needed.
The wheat and barley were harvested on July 13, and the oats on
July 26, with a combine and weights were made at the time of harvest.
The harvested area of each sub-plot was 63 inches (9X7 inches) by 40 feet. The c o m was hand harvested and weighed from an area 14 feet (4 rows) by 30 feet of each sub-plot on September 28. Moisture percentages were determined on a sample of c o m from each plot by a Steinlite
Electronic Moisture Tester and yields were calculated on the basis of
15.5 per cent moisture. The soybeans were hand harvested and threshed with a portable thresher on September 30. The harvested area was 14 feet
(4 rows) by 30 feet. 28
The sub-plots, where small grain was harvested, were disked and seeded to Balbo rye on August 1, 1960. Dual wheat was seeded on the corn and soybean sub-plots on October 12, 1960. These seedings were observed for crop injury shortly after emergence and in March 1961.
The movement of simazine in soil in the field
To determine quantitatively the simazine residual in the field plots and its distribution in the soil profile, samples of soil were taken from each plot on October 15, 1959. The soil was sampled at the 0 to
3-inch, 3 to 6 -inch and 6 to 9-inch levels. The sampling areas were 2 feet by 3 feet and were selected near the center of each plot. All sam ples of each soil level of plots receiving the same amount of simazine were bulked, thoroughly mixed and sifted through a 1/4-inch screen.
To have bioassay standards to compare with the field treated soil, simazine was applied to untreated soil at rates of 0.125, 0.25, 0.5, 1.0,
1.5, 2.0 and 2.5 pounds per acre. The simazine was thoroughly mixed with the soil because any simazine residual in the field treated soil was likewise mixed throughout the soil samples. Three replicates of the field treated and freshly treated soil were placed in No. 10 metal con tainers (6 inches in diameter by 7 inches deep) and Clinton oats were seeded as the bioassay crop on November 13, 1959. A total of 57 con tainers were used in this study (4 treatments X 3 soil levels X 3 repli cations plus 7 bioassay standards X 3 replications). The containers were completely randomized in the Department of Agronomy greenhouse at The
Ohio State University. After the oat seedlings emerged, they were thinned to twenty plants per container. The containers were individually 29 watered with tap water as needed. The tops of the oat plants were har vested and fresh weights made on December 5, 1959. The three replicates of each sample or treatment was then rebulked, mixed, sifted through a
1/4-inch screen and replaced into the containers. Clinton oats were again seeded in the containers on December 19, 1959, and identical pro cedures were followed as in the first planting. The tops of the oat plants were harvested and fresh weights made on January 12, 1960.
Samples of the field plots were again taken on May 12, 1960, approx
imately one year after the original simazine application. The samples were taken from the small grain sub-plots because they had not been plowed after the simazine was applied. The procedures of sampling and preparing the soil for the bioassay crop were identical to those of the first sampling. Bioassay standards were included and successive oat crops were grown on the soil. The first seeding was made on May 19,
1960, and harvested June 15, 1960. The second seeding was made on
August 15, I960, and harvested on September 10, 1960.
A third set of soil samples were taken from the field plots on
October 10, 1960, 17 months after simazine was applied. Again the same procedures as described for the first sampling were used. The first oat seeding on this sampling was made on October 13, 1960, and harvested
November 12, 1960. The second seeding was made on November 15, 1960, and harvested on December 12, 1960.
The movement of simazine and atrazine in soil in the laboratory
To compare the extent of leaching of simazine and atrazine, two different soils were selected. One was Hoytville clay, hereafter called 30
clay soil, which was obtained from The Ohio State University North western Substation near Hoytville, Ohio. The clay soil was from the top
six inches of an area that had been in a corn-small grain-meadow rotation
for several years. The other soil was Warsaw sandy loam, hereafter called
sandy soil, which was taken from a non-cultivated embankment on The Ohio
State University Agronomy Farm, Columbus, Ohio. A soil test and mechan
ical analysis revealed the following data:
Clay soil Sandy soil
Sand, per cent 19.7 50.2
Silt, per cent 39.0 34.1
Clay, per cent 41.3 15.7
Organic matter, per cent 2.5 3.0
PH 6.4 6 . 0
The soil was sifted through a 1/4-inch screen and allowed to air dry for
several months.
The method used to determine herbicide movement in soil was similar
to that described by Crafts (25) and Levi and Crafts (52). Instead of
using celluloid plates bent into forms of cylinders, heavy cardboard ice
cream cartons were used to form columns of soil. The herbicides were
applied to the surface of the soil columns and varying amounts of water
were applied. The cartons and soil were then sliced into one inch layers
and oats seeded in the soil as the bioassay crop.
A total of 144 cartons were required. Simazine and atrazine were
separately applied to each soil and a check of each soil was needed,
thus, six different soil treatments were prepared. Four levels of water 31 were applied to each soil treatment making 24 soil X water treatments.
Six replicates were prepared for each of the soil X water treatments.
The soil was placed into quart-sized ice cream cardboard cartons
(3 1/4 inches in diameter and 6 1/2 inches deep). It was lightly tamped in the cartons. A kilogram of soil filled the cartons to within one inch of the top which resulted in soil columns 5 1/2 inches long. Several holes were punched in the bottoms of the cartons to allow for drainage.
On July 6 , 1960, the soil in the cartons was moistened to field capacity by applying sufficient tap water to cause some drainage from the bottoms of the cartons. After allowing two days for the moistened soil to reach equilibrium, simazine and atrazine were applied to the soil surface at a rate of three pounds per acre. The surface area of each carton of soil was 8.2958 square inches. The herbicides were 80 per cent wettable powders; therefore, the rate of application of formulated material was
3.75 pounds per acre or 2.2516 mg. per carton. It was virtually impossi ble to weigh and uniformly apply this small amount of dry material. The solubility of the herbicides in water was so low that it required an excess amount of water to get the desired amount of herbicide in solution.
To attempt to keep the material in suspension in a lesser amount of water, when taking and applying aliquots of the suspension, would have very likely resulted in non-uniform rates of application. To use a solvent such as methyl alcohol or chloroform could have altered the leachibility of the herbicides once applied to the soil.
It was decided to mix the herbicides with soil in a proportion so that approximately 1/4 inch of soil applied to each carton would contain the 2.2516 mg. of herbicide. A layer of soil 1/4 inch thick with the 32 diameter of the cartons weighed approximately 45 grams; therefore,
67.548 grams of each herbicide (80% formulation) were separately placed in 1350 grams of each soil. This amount was sufficient for 30 cartons of each treatment, thus allowing for spillage, etc. Each of the mixtures was mixed for four hours on an electrically operated soil mixer. On
July 8 , 1960, 45 grams of each of the four mixtures were uniformly applied to the 24 appropriate cartons of soil.
Tap water was applied to the soil surface at rates of 0, 1, 2 and
4 inches. Application of water was made on July 8 , except the 4-inch rate on the clay soil was slow to penetrate and it was completed on
July 9. After application of water, tight fitting tops were placed on
the cartons to prevent surface evaporation. Two days were allowed for drainage and complete equilibrium of the water in the sandy soil and four days in the clay soil.
The sandy soil columns and cartons were sliced into 5 one-inch sec
tions on July 11, 1960, and the clay on July 13. About 1/2 inch of soil was left at the bottom of each carton, which was discarded. A special device for holding the cartons for slicing was designed. A sharp corn knife was used to make distinct one-inch slices.
The same levels of soil of the six replications of each treatment were bulked; i.e., the six 0 to 1 -inch soil layers of the clay soil
treated with simazine and one inch of water were bulked and likewise for
the other 23 treatments. The soils were allowed to dry sufficiently to
be mixed and sifted through a 1/4-inch screen. The soil was placed in
pint cartons with three replicates of each soil level of each treatment,
totaling 360 cartons of soil. Clinton oats were seeded in the cartons of 33 soil on July 18. The cartons were arranged in a completely randomized design in the Department of Agronomy greenhouse. The soil was watered as needed with tap water. After emergence, the oats were thinned to ten seedlings per carton. The oat tops were harvested and fresh weights made on August 13, 1960.
The effect of soil microorganisms on the breakdown of simazine and the effect of simazine on the activity of soil microorganisms
The effect of soil microorganisms on the breakdown of simazine and conversely, the effect of simazine on the activity of soil microorganisms were determined by the same experiment. C^-labeled simazine was applied to soil and the evolved carbon dioxide and carbon^ dioxide were collected and measured quantitatively and qualitatively. The amount of carbon dioxide evolved was a measure of the activity of the soil microorganisms and the relative radioactivity of the precipitated carbon dioxide (barium carbonate) was a measure of the breakdown of the simazine by the microorganisms.
The soil selected for this experiment was Brookston silty clay loam which was obtained from the top six inches of a crop rotation plot on The
Ohio State University Agronomy Farm, Columbus, Ohio. It contained 14.1 per cent sand, 46.4 per cent silt and 39.5 per cent clay. The pH of the soil was 6.2 and the organic matter content was 6.5 per cent. The soil was sifted through a 1/4-inch screen, air dried and stored for several months. The experiment was conducted in the Department of Agronomy lab oratory in Townshend Hall at The Ohio State University.
One hundred grams of air-dry soil was weighed into glass tumblers and C^-labeled simazine was applied to the soil surface at a rate of 34
3 pounds per acre or 1 mg. per tumbler. The specific activity of the material per tumbler was 5.524 microcuries. A stock solution of C ^ - labeled simazine was prepared using methyl alcohol as the solvent. The concentration was 1 mg. of simazine per 5 ml. of alcohol; therefore, 5 ml. were applied uniformly to the soil surface with a pipette. Two hours were allowed for the evaporation of the alcohol and then 25 ml. of water were added to bring the soil to approximately field capacity.
C^-labeled 2,4,5-T and amiben (3-amino-2,5-dichlorobenzoic acid) treated soils were analyzed concurrently with the simazine. Also included were tumblers of soil with no herbicidal treatments and blank tumblers. The treatments were replicated four times and arranged in a completely randomized design.
Immediately after application of water, the tumblers were attached to an aspiration apparatus in a constant temperature room. The tempera ture was maintained at 28°C. for the duration of the experiment. The aspiration apparatus and method of collecting and determining volumetri- cally the amounts of CO2 evolved is a modification of that described by
Heck (45) and is similar to the methods used by Bondarenko (13) and
Teater (90). Air, under pressure, passed through two "scrubbing" con tainers of 4N. NaOH to remove the C0 2 » and bubbled through CO2 free, dis tilled water to saturate it. It then passed through a glass manifold with outlets along each side. The tumblers with soil were attached to
the manifold outlets by means of a length of Tygon tubing, containing short sections of glass capillary tubing which helped regulate the pres sure in the system. The air was passed through the manifold, over the soil in the tumblers and into stoppered glass tumblers containing 10 ml. of 2.014 NaOH solution, 25 ml. of CO2 free distilled water and a glass bead bubbling tower. The CO2 was absorbed by the NaOH forming Na 2C03
(CO2 + 2 NaOH— >Na 2C0 3 + H 2O). After each collection period the tumblers and towers were removed and washed down with CO2 free water. The Na2C03 was precipitated as BaC03 by the addition of an excess of BaCl2 (Na2C03 4.
BaCl2— >BaC 03 + 2 NaCl). The samples were then titrated with standard
HC1 to a pH of 8.5 to determine the amount of unused NaOH still present in the tumblers. The titration was done with a Beckman "Model K" auto matic titrator. The actual amount of carbon lost from the soil was cal culated by the following formula: Mg. carbon = (ml. NaOH originally in collection tumbler X N. NaOH) - (ml. HC1 used in titration X N. HCl) X 6 .
The aspiration procedure was started February 11, 1961, and termin ated March 25, 1961, a period of 42 days. The CO2 collections were made twice weekly for the first two weeks and at weekly intervals thereafter.
After each collection the precipitated BaCC>3 was filtered and washed. It was then thoroughly dryed in an oven, placed in stoppered glass vials and stored in a desiccator. The BaC03 was finely ground in ethyl alcohol, put in plastic planchets and counted with a Geiger-Muller-
Nuclear scaler for relative amounts of radioactivity. Corrections were made for background, self-absorption, geometry, coincidence and daily efficiency of the counting apparatus. EXPERIMENTAL RESULTS AND DISCUSSION
The effect of simazine on weed population and corn yield
Simazine applied pre-emergence to corn on May 25, 1959, at rates of 2 , 4 and 8 pounds per acre resulted in excellent control of annual weeds. The weed population of the check plots consisted mainly of rough pigweed (Amaranthus retroflexus), lambsquarters (Chenopodium album) , smartweed (Polygonum spp.), common ragweed (Ambrosia artemisiifolia), wild mustard (Brassica kober), foxtail (Setaria spp.), crabgrass
(Digitaria spp.) and panicgrass (Panicum spp.). The number of broadleaf and grass weeds on a 175 sq. ft. area and the per cent reduction are pre
sented in Table 1.
Table 1. Number and per cent reduction of annual broadleaf and grass weeds in c o m treated pre-emergence with simazine on May 25, 1959. Counts were made on June 20, 1959, on 175 sq. ft. of each of 4 repli cates. Values are the average of 4 replications.
Simazine Number of Weeds Per Cent Reduction* lb/A Broadleaf Grass Total Broadleaf Grass Total
0 1 1 0 . 0 0 204.00 314.00 0. 0 0 . 0 0. 0
2 5.00 7.25 12.25 95.5 96.4 96.1
4 2.25 1.75 4.00 98.0 99.1 98.7
8 1.50 2.0 0 3.50 98.6 99.0 98.9
*Based on the check plots.
The 4 and 8 pounds per acre rate reduced the weed population
slightly more than did the 2 pound rate but from the practical and
36 37 economical viewpoint, the degree of weed control by the latter rate appeared sufficient for commercial use. There was virtually no differ ence in the reduction in stands of broadleaf weeds as compared to grass weeds.
There were no significant differences between the yield of corn from any of the simazine treated plots and the check plots (Table 2).
The average yield of all plots was 71.3 bushels per acre and the great est deviation of any of the treatment averages from this was 3.5 bushels.
Table 2. Yield of corn treated pre-emergence with simazine on May 25, 1959. Average of 4 replications.
Simazine, Yield lb/A bu/A
0 68.4
2 71.7
4 72.4
8 72.9
The effect of simazine soil residues on corn, wheat, barley, oats and soybeans
The yield of crops seeded subsequent to corn which had been treated pre-emergence with simazine are presented in Table 3 and graphically illustrated by Figure 2. Figures 3 through 7 are pictures of the crops prior to harvest.
The yield of corn was unaffected by all rates of simazine when com pared with the check plots. There were no significant differences in yields of wheat, barley, oats and soybeans when the yields of plots re ceiving 2 pounds of simazine per acre were compared with the check plots; 38 however, the reductions in yields of these crops at the 4 and 8 pounds of simazine per acre rates were significant. This residual effect was probably influenced somewhat by the relatively small amount of rainfall following the application of simazine (Table 4).
Table 3. Yield of com, wheat, barley, oats and soybeans following c o m treated pre-emergence with simazine. Values shown are the averages of four replications.
Simazine Yield, bu/A lb/A C o m Wheat Barley Oats Soybeans
0 78.2 50.9 78.1 95.1 33.2
2 79.6 51.8 81.0 86.7 33.0
4 79.4 28.9 39.8 48.7 21.5
8 83.2 4.0 15.3 10.5 9.1
LSD 0,05 NS 8.9 16.9 15.9 10.2
LSD 0.01 NS 12.8 24.3 22.8 14.6
Table 4. Rainfall at University Farm, Columbus, Ohio
1959, inches May 25-31 June July Aug. Sept. Oct. Nov. Dec.
0.98 0.96 3.10 0.94 1.53 2.83 3.31 2.42
1960, inches
Jan. Feb. March April May June July Aug.
2.36 2.95 1.00 2.15 5.03 3.74 5.30 4 . 0 0 iue . h il fcr,wet bre, as n obas following soybeans and oats barley, wheat, corn, of yield The 2. Figure corn treated pre-emergence with simazine. Yield is expressed as per cent per as expressed is Yield simazine. with pre-emergence treated corn f check. of Yield, per cent of check 100 110 0 2 Oats Wheat Soybeans Barley Corn iaie lb/A Simazine, 4 8 39
40
Figure 3. The growth of corn in 1960 in plots receiving (left) no sima- zine and (right) 8 pounds of simazine per acre. The simazine was applied in Hay 1959. 41
I HIIV. ttP 2 I.H/A I [Am. mi g/g«|j [ iviiiriV" |hh»:ih:i) n/5!> IPicrum: 7/nit
Figure 4. The growth of wheat in 1960 in plots receiving (top left) no simazine, (top right) 2 pounds of simazine per acre and (bottom) 8 pounds of simazine per acre. The simazine was applied in May 1959;- 42
H,Mil.IV [si.nii ii vi/siil tMCTlim 7/(ill
I nnm.fr Uc^oiij a/in 7/Bnj
Figure 5. The growth of winter barley in 1960 in plots receiving (top left) no simazine, (top right) 2 pounds of simazine per acre, (bottom left) 4 pounds of simazine per acre and (bottom right) 8 pounds of simazine per acre. The simazine was applied in May 1959. ItMinMi■ • ll/I . r «m Isiriirj)/^ iih 4 PlftfUMt 7/toy
Figure 6 . The growth of spring oats in 1960 in plots receiving (top left) no simazine, (top right) 2 pounds of simazine per acre and (bottom) 8 pounds of simazine per acre. The simazine was applied in May 1959. 44
Figure 7. The growth of soybeans in 1960 in plats receiving (top left) no simazine, (top right) 2 pounds of simazine per acre, (botfiom left) 4 pounds of simazine per acre and (bottom right) 8 pounds of simazine per acre. The simazine was applied in May 1959. 45
Between Hay 25, 1959, and May 24, 1960, 27.85 inches of rainfall, approximately 10 inches less than normal, were recorded at the University
Farm. It is conceivable that an additional ten inches of rainfall would have reduced the residual phytotoxicity of the simazine.
There was no apparent injury to the rye seeded on the small grain plots or to the wheat seeded on the c o m and soybean plots when observed
December 3, 1960, and April 6 , 1961.
The effect of simazine soil residues on the legume-grass seedings could not be determined because there were poor stands of the seeding mixtures on all plots, including the non-treated plots.
The movement of simazine in soil in the field
The growth of the oat bioassay crops grown in soil treated with simazine at 2, 4 and 8 pounds per acre was significantly reduced on the soil samples taken October 15, 1959, five months after the application of simazine (Tables 5 and 6 and Figure 8 ). There was a significant reduction in growth at all rates of simazine in the 0 to 3 and 3 to
6 -inch soil levels but not the 6 to 9-inch level. There was no signifi cant difference in growth between the 0 to 3 and 3 to 6 -inch levels at
2 pounds per acre but the 4 and 8 pounds per acre rates caused a signi ficant difference in growth response between these two soil levels, indicating that a greater per cent of the simazine remained in the top three inches of soil at the higher rates (Figure 9). There was no signi ficant difference in growth response between the 4 and 8 pounds per acre rates at any soil level. 46
Table 5. Weight of first crop of oat seedlings grown in soil taken on October 15, 1959, from field plots treated with simazine on May 25, 1959. Values are grams of fresh weight and are the average of three replications.
Simazine Soil level, inches lb/A 0-3 3-6 6-9 Average
0 6.491 6.981 6.543 6.671
2 2.925 3.213 “ 7.321 4.486
4 0.670 1.806 7.728 3.401
8 0.215 1.427 7.444 3.041
Average 2.584 3.357 7.259 4.400
LSD for simazine treatment means - 0.05 0.524 0.01 0.710
LSD for soil level means ----- 0.05 0.454 0.01 0.615
LSD for interaction values - - - - 0.05 0.907 0.01 1.229
In comparing the weights of the oat seedlings grown in the soil
taken from the simazine treated field plots on October 15, 1959, to those
grown for bioassay standards (Table 7 and Figure 8), approximately 1/4
pound per acre of simazine remained in the 0 to 3 and 3 to 6-inch soil
levels but none in the 6 to 9-inch level. These figures may not repre
sent the amount of actual simazine remaining in its original form but
the phytotoxic effect of the soil residues on oats was equivalent to the
reported rates of freshly applied simazine. Hereafter this will be
referred to as the simazine equivalent. Plots treated with simazine at
4 pounds per acre contained approximately 11/2 pounds of simazine
equivalent per acre in the 0 to 3-inch soil level, 1/3 pound in the 3 to 47
Table 6. Weight of second crop of oat seedlings grown in soil taken on October 15, 1959, from field plots treated with simazine on May 25, 1959. Values are grams of fresh weight and are the average of three replications.
Simazine Soil level, inches lb/A 0-3 3-6 6-9 Average
0 7.329 7.977 7.309 7.538
2 3.319 4.130 7.899 5.116
4 0.849 2.224 8.535 3.869
8 0.473 1.965 8.151 3.530
Average 2.993 4.074 7.974 5.013
LSD for simazine treatment means - 0.05 0.435 0.01 0.589
LSD for soil level means - - - - 0.05 0.377 0.01 0.510
LSD for interaction values - - - - 0.05 0.753 0.0 1 1.020
Table 7. Bioassay standards for weight of oat seedlings grown in soil freshly treated with simazine and randomized with soil taken from field plots on October 15, 1959. Values are grams of fresh weight and are the average of three replications.
Simazine, lb/A 0 0.125 0.25 0.5 1.0 1.5 2.0 2.5
Oat seedlings, gm 7.105 4.678 2.954 1.106 0.881 0.764 0.476 0.389
Per cent reduction 0 34.2 58.2 84.4 87.6 89.3 93.3 94.5 48
100
2.5 2.0
09 M o 0) M u a o •o 4) 09 a 70 09
H •0 0 0» 0.25 09 4Js
0 (bioassay (bioassay standard)
•0.125 Simazine equivalent, lb/A § 4J U 0 to 3-inch soil level 4 0 M 3 to 6-inch soil level 4J fi 0 o 6 to 9 -inch soil level M 0 Pk
Simazine, lb/A
Figure 8. Reduction in weight of oat seedlings grown in simazine treated soil taken from field on October 15, 1959, and oats grown for bloassay standards. Percentages are based on fresh weight of three replications of two successive crops. 49
1 SIMMIX niUXH I |.n/ii !l IKl-.ll sinLPW-IKI) MKSfl iMM sun.
Figure 9. The growth of oats in soil taken from field plots on October 15, 1959, five months after the application of simazine. Top (left to right), soil of the 0 to 3, 3 to 6 and 6 to 9-inch levels from plots receiving 2 pounds of simazine per acre and the corresponding checks. Center (left to right), soil of the 0 to 3, 3 to 6 and 6 to 9-inch levels from plots receiving 4 pounds of simazine per acre and the corresponding checks. Bottom (left to right), soil of the 0 to 3, 3 to 6 and 6 to 9- inch levels from plots receiving 8 pounds of simazine per acre and the corresponding checks. 50
6 - inch level and none in the 6 to 9-inch level. Plots treated with 8 pounds of simazine per acre contained approximately 2 1/2 pounds of
simazine equivalent in the 0 to 3-inch soil level, 1/3 pound in the 3
to 6 -inch level and none in the 6 to 9-inch level.
The 1 1/2 to 2 1/2 pounds of simazine equivalent in the soil five months after the original application was reflected in the reduction of yields of wheat and barley as reported earlier. These crops were seeded at the time the soil samples were taken. The 1/4 pound per acre in plots originally treated with 2 pounds of simazine per acre did not
reduce the yields of wheat and barley which are reported as being more
tolerant to simazine than the bioassay crop, oats.
Soil samples taken May 12, 1960, one year after the original
application of simazine, from field plots treated with 2 pounds of
simazine per acre contained no soil residual at any soil level as deter mined by the bioassay crop (Tables 8 and 9 and Figure 10). There was a
significant reduction in growth of the bioassay crop in the 0 to 3 and
3 to 6-inch soil levels in soil from the plots treated with 4 and 8
pounds of simazine per acre. Soil from the 6 to 9-inch soil level in
plots treated with 4 pounds per acre did not reduce the plant growth while there was some reduction at the lower level of the plots treated with 8 pounds per acre; however, the reduction was not statistically
significant.
The simazine equivalent in the soil taken one year after the plots were treated with simazine at 4 pounds per acre was approximately 1/3
pound per acre in the 0 to 3-inch soil level and less than 1/8 pound in
the 3 to 6 -inch level (Table 10 and Figure 10). In plots treated with 51
8 pounds of simazine per acre, there was approximately 11/2 pounds
simazine equivalent per acre at the 0 to 3-inch soil level, 1 1/4 pounds at the 3 to 6-inch level and less than 1/8 pound at the 6 to 9-inch
level. Again the simazine equivalent in plots treated with 4 and 8 pounds per acre was reflected by the reduction in the yields of soybeans and oats which were seeded approximately the same time the soil samples were taken.
Table 8. Weight of first crop of oat seedlings grown in soil taken on May 12, 1960, from field plots treated with s imazine on May 25, 1959. Values are grams of fresh weight and are the average of three replica tions.
Simazine Soil level, inches lb/A 0-3 3-6 6-9 Average
0 6.838 6.812 6.162 6.604
2 6.728 7.166 6.181 6.692
4 1.962 5.347 6.413 4.574
8 0.606 0.901 5.455 2.321
Average 4.034 5.057 6.053 5.048
LSD for simazine treatment means - 0.05 0.772 0.01 1.047
LSD for soil level means ----- 0.05 0.669 0.01 0.907
LSD for interaction values - - - - 0.05 1.338 0.01 1.814
The two successive bioassay oat crops grown on the soil samples
taken October 10, 1960, seventeen months after the original simazine
application, differed somewhat in growth (Tables 11 and 12 and Figure 11). 52
There were no significant differences in growth at any soil level in the soil taken from the 2 and 4 pounds per acre rates in either of the successive bioassay crops. There was a reduction of growth, significant at the 5 per cent level, in the 0 to 3-inch soil level of plots treated with 8 pounds of simazine per acre, as determined by the first bioassay crop but no differences at any soil level were determined by the second crop. The simazine equivalent of the 0 to 3-inch soil level of the first crop was less than 1/8 pound per acre (Table 13 and Figure 11).
Table 9. Weight of second crop of oat seedlings grown in soil taken on May 12, 1960, from field plots treated with simazine on May 25, 1959. Values are grams of fresh weight and are the average of three replica tions .
Simazine Soil level, inches lb/A 0-3 3-6 6-9 Average
0 5.516 5.532 4.940 5.330
2 6.526 6.419 4.875 5.940
4 1.347 3.981 5.441 3.590
8 0.134 0.179 4.486 1.600
Average 3.381 4.028 4.936 4.115
LSD for simazine treatment means - 0.05 0 . 8 8 6 0 . 0 1 1 .201
LSD for soil level means ------0.05 0.768 0 . 0 1 1.040
LSD for interaction values ------0.05 1.535 0 . 0 1 2.081 53
100
.2.0
90- 0.5 a 0 to 3-inch soil level M o ja4> - 3 to 6-inch soil level o 80 e o 6 to 9 -inch Boil T3 level 4) a <0 70
■0.25 •o 41 60 « CO 4J m o M-l 50 o
0.125 (bioassay (bioassay standard) Simazine Simazine equivalent, lb/A 30 o 3 4) VI
Os
£ 10
Simazine, lb/A
Figure 10. Reduction in weight of oet seedlings grown in simazine treated soil taken from field on Hay 12, 1960, and oats grown for bioassay standards. Percentages are based on fresh weight of three replications of two successive crops. 54
Table 10. Bioassay standards for weight of oat seedlings grown in soil freshly treated with simazine and randomized with soil taken from field plots on May 12, 1960. Values are grams of fresh weight and are the average of three replications.
Simazine, lb/A 0 0.125 0.25 0.5 1.0 1.5 2.0
Oat seedlings, gm 5.967 4.076 2.159 0.700 0.569 0.386 0.314
Per cent reduction 0 39.7 63.8 88.3 90.5 93.5 94.7
Table 11. Weight of first crop of oat seedlings grown in soil taken on October 10, 1960, from field plots treated with simazine on May 25, 1959. Values are grams of fresh weight and are the average of three replica tions.
Simazine Soil level, inches lb/A 0-3 3-6 6-9 Average
0 7.251 7.214 6.887 7.117
2 7.001 7.300 6.793 7.031
4 6.978 7.173 6.969 7.040
8 5.453 6.548 6.813 6.271
Average 6.671 7.059 6 . 8 6 6 6.865
LSD for simazine treatment means - 0.05 0.413 0 . 0 1 0.559
LSD for soil level means - - - - - 0.05 NS
LSD for interaction values - - - - 0.05 0.715 0 . 0 1 NS 55
Table 120 Weight of second crop of oat seedlings grown in soil taken on October 10, 1960, from field plots treated with simazine on May 25, 1959. Values are grams of fresh weight and are the average of three replications.
Simazine Soil level, inches lb/A______0-3______3-6______6-9______Average
0 6.471 6.350 5.945 6.255
2 6.087 5.973 6.291 6.117
4 6.357 6.329 5.900 6.195
8 4.902 5.866 5.906 5.558
Average 5.954 6.130 6.010 6.031
Table 13. Bioassay standards for weight of oat seedlings grown in soil freshly treated with simazine and randomized with soil taken from field plots on October 10, 1960. Values are grams of fresh weight and are the average of three replications.
Simazine, lb/A 0 0.125 0.25 0.5 1.0 1.5 2.0
Oat seedlings, gm 6 . 6 8 6 4.804 2.824 0.926 0.587 0.356 0.215
Per cent reduction 0 29.2 57.8 86.2 91.2 94.7 96.8 56
100 2.0 1.5
90 • 1.0 co u 0) JC o d o 0.5 •o 4) (0 (0 jQ
•d
o
V 0 to 3-inch soil level d 3 to 6-inch soil level (bioassay standard) Simazine Simazine equivalent, lb/A
u 30 6 to 9-inch soil level 0.125 o •3 4) 4J d 4) U t-i 4) PH 1 0 '
0 4 82
Simazine, lb/A
Figure 11. Seduction in weight of oat seedlings grown in simazine treated soil taken from field on October 10, 1960, and oats grown for bioassay standards. Percentages are based on fresh weight of three replications of two successive crops. 57
The movement of simazine and atrazine in soli in the laboratory
The weights of oat seedlings grown in two types of soil, which had varying rates of water applied to the treated soil surface, were used
to indicate the relative amounts of herbicide at one inch intervals.
The plant growth in soil treated with atrazine was significantly reduced when compared with that in simazine treated soil and both were signifi
cantly reduced when compared with the check (Table 14). This was true
considering both the sand and clay soils.
Atrazine and simazine were leached into the 3 to 4 and 4 to 5-inch
levels of the sandy soil in significantly greater quantities than in the
clay soil as indicated by the growth response (Table 14). The herbi
cides were leached equally into the 0 to 1 and 1 to 2-inch levels of
both soils but there was more of each material in the clay soil at the
2 to 3-inch level than in the sandy soil, which was the reverse of the
lower levels. This indicates that the herbicides were leached to the
2 to 3-inch level in the clay soil and accumulated there more than they
did in the sandy soil.
The plant growth in soil treated with atrazine and leached with 1,
2 and 4 inches of water was significantly less than that in simazine
treated soil with corresponding rates of water (Table 15 and Figure 12).
However, where no water was applied for leaching, the atrazine treated
soil supported more oat growth than did that treated with simazine.
As expected, the 4 inches of applied water leached larger quanti
ties of both herbicides to a lower level than did 1 or 2 inches. More
plant growth occurred at the lowest soil level in every instance where Table 14. Weight of oat seedlings grown in two soil types treated with atrazine and simazine. Water was applied to the treated soil surfaces and the soil columns were sectioned into five one-inch levels. Values are grams fresh weight and are the average of three replications.
Herbicide treatment Atrazine Simazine Check Soil level, Soil type Soil type Soil type Overall inches Sand ClayAverage Sand ClayAverage Sand Clay Average Average
0 - 1 0.088 0.065 0.076 0.091 0.079 0.085 3.384 3.367 3.530 1.230
1 - 2 1.727 1.714 1.721 1.797 1.935 1.866 3.275 3.693 3.484 2.357
2-3 2.464 2.092 2.278 2.668 2.206 2.437 3.428 3.462 3.445 2.720
3 - 4 2.565 2.858 2.711 2.610 2.819 2.714 3.263 3.690 3.476 2.967
4 - 5 2.530 3.027 2.778 2.809 3.396 3.103 3.378 3.519 3.449 3.110
Average 1.875 1.951 1.913 1.995 2.087 2.041 3.346 3.608 3.477 2.477
LSD for herbicide treatment means - 0.05 0.076 0 .0 1 0 . 1 0 0 LSD for soil level means------0.05 0.098 0 . 0 1 0.129 LSD for herbicide treatment X soil level------0.05 0.171 0 .0 1 0.224 LSD for herbicide treatment X soil type - ...... - 0.05 0.108 0 . 0 1 NS LSD for herbicide treatment X soil level X soil type- - 0.05 0.242 0 . 0 1 0.381
in 00 Table 15. Weight of oat seedlings grown in two soil types treated with atrazine and simazine. Four rates of water were applied to the treated soil surfaces. Values are grains fresh weight and are the average of three replications.
Herbicide treatment Atrazine Simazine Check Water rate, Soil type Soil type Soil type Overall inches Sand ClayAverage Sand Clay Average Sand Clay Average Average
0 2.610 2.796 2.703 2.524 2.570 2.547 3.394 3.548 3.489 2.913
1 2.677 2.518 2.598 2.929 3.005 2.970 3.266 3.516 3.391 2.985
2 2.127 2.268 2.197 2.399 2.284 2.342 3.475 3.623 3.549 2.696
4 0.085 0 . 2 2 2 0.153 0.128 0.489 0.309 3.247 3.709 3.478 1.313
Average 1.875 1.951 1.913 1.995 2.087 2.041 3.346 3.608 3.477 2.477
LSD for herbicide treatment means ------0.05 0.076 0. 0 1 0 . 1 0 0
LSD for water rate; means- - - 0.05 0.088 0. 0 1 0.116
LSD for herbicide treatment X water rate------0.05 0.153 0.0 1 0 . 2 0 1
LSD for herbicide treatment X soil type ------0.05 0.108 0 . 0 1 NS 'j LSD for herbicide treatment X water rate X soil type- - 0.05 NS Ui vO Figure 12. The growth of oats in clay soil treated with atrazine (top row) and simazine (bottom row). Duplicate pots from left to right in each picture are 0 to 1, 1 to 2, 2 to 3, 3 to 4, 4 to 5-inch soil levels and the corresponding check. The soil in the pictures from left to right received no water, 1 inch, 2 inches and 4 inches of water after the herbicides were applied. 61 water was used to leach atrazine or simazine, indicating that the reten tion of most of the herbicides was at or near the soil surface (Table 16).
Although there were significant differences in plant growth due to different herbicide treatments, different soil types and different rates of water used to leach the herbicides downwardly, the variations were not markedly different (Figure 13). The herbicide treatment X soil type and the water rate X soil type interactions were significant at only the
5 per cent level and the herbicide treatment X water rate X soil type interaction was not significant. With one herbicide (atrazine) sixteen times as soluble in water as the other and with soils that vary consider ably in physical characteristics and chemical composition, one might expect differences of greater magnitude.
The effect of soil microorganisms on the breakdown of simazine
The BaC(>3 , which contained C(>2 evolved from soils treated with simazine, contained more isotopic carbon^ atoms than did the CO2 from non-treated soil. Since the carbon^ atoms were uniformly distributed in the triazine ring, the evolution of C ^ 0 2 resulted from splitting the ring, indicating complete decomposition of the basic structure of simazine.
The BaC0 3 samples from the non-treated soils contained no more radioactivity (counts per minute of beta ray emissions) than was recorded for background. This was expected because carbon^ has been found to be relatively uniformly distributed in the atmosphere and soil.
The maximum counts per minute per milligram of carbon (cpm/mg C) was obtained from the material which accumulated during the third week of the incubation period (Figure 14). However, the maximum decomposition 62
Table 16. Weight of oat seedlings grown in soil treated with atrazine and simazine. Four rates of water were applied to the treated soil sur faces and the soil columns were sectioned into five one-inch levels. Values are grams fresh weight and are the average of three replications.
Soil level, Herbicide Water rate , inches inches treatment 0 1 2 4 Average
0 - 1 Atrazine 0.078 0.078 0.071 0.080 0.076
Simazine 0.089 0.083 0.082 0.087 0.085
Check 2.433 3.509 3.560 3.617 3.530 Average 1.200 1.223 1.238 1.261 1.230
1 - 2 Atrazine 2.910 2.559 1.335 0.079 1.721
Simazine 2.915 2.876 1.585 0.089 1.866
Check 3.505 3.379 3.496 3.556 3.484 Average 3.110 2.938 2.139 1.241 2.357
2-3 Atrazine 3.031 2.953 3.056 0.072 2.278
Simazine 2.889 3.650 3.108 0 . 1 0 2 2.437
Check 3.437 3.385 3.637 3.322 3.445 Average 3.119 3.329 3.267 1.165 2.720
3-4 Atrazine 3.862 3.696 3.198 0.089 2.711
Simazine 3.228 4.061 3.368 0.199 2.714
Check 3.458 3.453 3.626 3.369 3.476 Average 3.516 3.737 3.397 1.219 2.967
4-5 Atrazine 3.634 3.703 3.329 0.447 2.778
Simazine 3.614 4.164 3.566 1.066 3.103
Check 3.615 3.228 3.424 3.528 3.499 Average 3.621 3.698 3.440 1.681 3.110
Overall Average 2.913 2.985 2.696 1.313 2.477 63
Table 16. Continued
LSD for water rate means ------0.05 0.088 0 . 0 1 0.116
LSD for soil level means ------0.05 0.098 0.01 0.129
LSD for water rate X soil level------0.05 0.197 0.01 0.259
LSD for herbicide treatment X soil level ------0.05 0.171 0.01 0.224
LSD for herbicide treatment X water rate X soil level- - - 0.05 0.341 0.01 0.449 ee etoe it n-nh aes Vle ae xrse s e eto check. of cent per as expressed are Values layers. one-inch into sectioned were Figure 13. Relative weight of oat seedlings grown in two soil types treated with atrazine and atrazine with treated types soil two in grown seedlings oat of weight Relative 13. Figure iaie Fu ae o ae eeapid o h tetd ol ufcs n te ol columns soil the and surfaces soil treated the to applied were water of rates Four simazine. Weight of oat seedlings, per cent of check 100 40 90 30 70 80 50 20 10 60 Atrazine d • •d t r o w cd rt d «> «d f-t fe
Simazine o • •o f U .■< U Cfl T-t V O .0) CO B >
o i taieSimazine Atrazine h cm i i i i •
ro<* in n ol ee, in. level, Soil n o i f < O N H cm i i i ii co «$■ in Atrazine 12 4 2 1 0 ae rate, Water
12 4 2 1 0 Simazine in. ____
Counts per minute per milligram of carbon Values are expressed in counts per minute of beta ray emissions and per cent maximum decomposi maximum cent per and emissions ray beta of minute per counts in expressed are Values Figure 14. Die radioactivity of BaCC> of radioactivity Die 14. Figure labeled simazine, and the relative amounts of simazine decomposition, measured at weekly intervals. at weekly measured decomposition, simazine of amounts relative the and simazine, labeled tion of simazine and are the average of four replications. four of average the are and simazine of tion 10 4 1 0 3 2 5 6 7 8 9 1 — — Per cent maximum decomposition maximum cent Per — — Cpm/mg C Cpm/mg 2 3 , formed from CO from , formed 3 Time in weeks in Time 2 evolved from soil treated with carbon^- with treated soil from evolved 4 5 6 - 80 40 30 50 100
Per cent maximum decomposition of simazine (cpm/mg G X mg C accumulated/collection period) of simazine occurred during the second week because of the relatively large quantity of CO2 evolved during that period. After the third week, the cpm/mg C were fairly constant, which indicated that the microorganisms capable of decomposing simazine were not increasing in number or activity. The curve indicating the relative amounts of simazine decomposed by microorganisms at weekly intervals (Figure 14) was similar to that showing the weekly accumulation of carbon (Figure 15). The results of this study were in agreement with the findings of Sheets and Danielson (83) who reported that the action of soil microorganisms on simazine appeared to be passive in that the organisms utilized it but not select ively or preferentially. If the reverse of this were true, one would expect the cpm/mg C evolved from treated soil to increase as time elapsed. The effect of simazine on the activity of soil microorganisms The activity of the soil microorganisms, as measured by carbon dioxide evolution, was not altered when simazine was applied at a rate of 3 pounds per acre. The amount of carbon, evolved as GO2 from the simazine treated soil, accumulated at weekly intervals and for the dura tion of the experiment, closely paralleled that of the non-treated soil (Table 17, Figures 15 and 16). The amount of CO2 evolved weekly from both soils reached a peak at the end of the second week and tapered off thereafter, with an excep tion of a slight increase at the end of the fifth week. The early peak is typical of soils which have been stored under dry conditions and then Figure 15. Weekly accumulation of carbon, evolved as CO as evolved carbon, of accumulation Weekly 15. Figure treated and simazine treated soil. Values are the average of four replications. four of average the are Values soil. treated simazine and treated Carbon, mg. 40 50 Time in in weeks Time o-rae soil Non-treated Simazine treated soil treated Simazine 2 , from 100 grams of non of grams 100 , from a\ 180 160 140 120 a o •B 3 Simazine treated soil — — Non-treated soil 40 20 0 4 7 11 1421 28 35 42 Time in days Figure 16. Total accumulation of carbon, evolved as C02» from 100 grams of non- treated and simazine treated soil. Values are the average of four replications. 69 moistened and incubated. The slight increase after five weeks of incu bation is unexplainable. Table 17. Amount of carbon, evolved as carbon dioxide, from 100 grams of non-treated and simazine treated soil. Values are grams of carbon and are the average of four replications. Total accumulation Date of Days after Carbon, mg. of carbon, mg. collection treatment Simazine Check Simazine Check 2/15/61 4 10.86 16.59 10.86 16.59 2/18/61 7 29.61 15.14 40.47 31.73 2/22/61 11 28.11 19.94 68.58 51.67 2/25/61 14 19.61 18.75 88.19 70.42 3/4/61 21 28.44 32.39 116.63 102.81 3/11/61 28 17.54 18.90 134.17 121.71 3/18/61 35 19.97 26.92 154.14 148.63 3/25/61 42 15.64 16.91 169.78 165.54 SUMMARY AND CONCLUSIONS The objectives of this study were to determine the effect of simazine on corn and weeds and its residual effect on the field crops which normally follow c o m in a rotation. Also studied were some fac tors which affect the persistence and distribution of simazine and atrazine in soils. The movement and disappearance of simazine in field soil and the movement of atrazine and simazine in sandy and clay soil columns were determined. The effect of simazine on the activity of soil microorganisms and the microbial breakdown of C^-labeled simazine were studied. On the basis of these experiments, the following conclusions were made: 1. Yields of winter barley and wheat, soybeans and spring oats, seeded at the normal seeding dates, following c o m which was treated pre-emergence with simazine at 2 pounds per acre, were not reduced. The yields of these crops were significantly reduced when seeded following the 4 and 8 pounds of simazine per acre. 2. On silty clay loam soil, more simazine was retained in the 0 to 3-inch soil level, five months after field application, than at the 3 to 6-inch level. No simazine was in the 6 to 9-inch level as deter mined by the oat bioassay crop. The plant growth on soil treated with 4 and 8 pounds of simazine per acre was significantly less than that in soil treated with 2 pounds. 70 71 3. When applied at 2 -pounds per acre, no residual of simazine was found in soil one year following application as evidenced by growth of the oat bioassay crop. There was a significant reduction in growth of the bioassay crop in the 0 to 3 and 3 to 6-inch soil levels in soil from plots treated with 4 and 8 pounds of simazine per acre. 4. Soil samples, taken seventeen months after the application of 2 and 4 pounds of simazine per acre, contained no simazine at any level as determined by the simazine-sensitive oat crop. There was evidence that a slight amount (less than 1/8 pound per acre) of simazine remained in the 0 to 3-inch level of plots receiving 8 pounds per acre. 5. Considering all rates of simazine and all dates of sampling and using oats as a bioassay crop, there was a slight residual of the 2 pounds per acre rate after five months but none after twelve and seven teen months. In soil treated with 4 and 8 pounds of simazine per acre, a residual was found in the 0 to 3 and 3 to 6 -inch level after five and twelve months. None was detected after seventeen months in the 4 pound rate and a slight amount in the 0 to 3-inch level of the 8 pound rate after that period. At no rates did the simazine move deeper into the soil than the 6 -inch plow layer. 6 . Atrazine and simazine were leached in greater quantities to the lower soil levels in sandy soil than in clay soil when measured in a laboratory leaching study. Atrazine was leached slightly more readily into the different soil levels than was simazine when 1 , 2 and 4 inches of water were applied to the treated soil surfaces. 7. The activity of soil microorganisms, as measured by carbon dioxide evolution, was not altered when simazine was applied at 3 pounds 72 per acre to the surface of tumblers of soil in a constant temperature room. The accumulation of carbon, evolved as CO2 , at weekly intervals and the total accumulation for six weeks from simazine treated soil, closely paralleled that of the non-treated soil. 8 . Radioactive carbon dioxide (C ^ 0 2 ) evolved from a silty clay loam soil that was treated with carbon^-labeled simazine while non- treated soil yielded non-radioactive CO2 , indicating that soil micro organisms completely decomposed some of the simazine molecules. Maximum radioactivity per unit of carbon was obtained from BaCOj samples which were precipitated from the CO2 collected during the third week of incu bation. Maximum simazine decomposition occurred during the second week of incubation. The decomposition of simazine throughout the incubation period was proportional to the amount of CO2 evolved. 9. Simazine applied pre-emergence to corn at 2, 4 and 8 pounds per acre resulted in 96, 99 and 99 per cent control of annual weeds, respectively, and did not cause any visual injury symptoms or alter the yield of Ohio Certified W-64. hybrid corn. LITERATURE CITED Agundis, 0. and D. D. Bondarenko. A comparison of granular and liquid formulations of herbicides on corn. Proc. of North Central Weed Control Conf. 16:81-82. 1959. Akamine, E. K. Persistence of 2,4-D toxicity in Hawaiian soils. Bot. Gaz. 112:312-319. 1951. Aldrich, R. J. Herbicides - residues in soils. Jour, of Agri. and Food Chem. 1:257-260. 1953. Alexander, M. Herbicides don't kill useful soil microbes. Soils and Crops 12:19. 1959. Anderson, L. E. Chemical weed control in corn. Proc. of North Central Weed Control Conf. 16:52. 1959. Audus, L. G. The decomposition of 2,4-dichlorophenoxyacetic acid and 2-methyl-4-chlorophenoxyacetic acid in the soil. Jour. Sci. Food and Agri. 3:268-274. 1952. ______. Microbiological breakdown of herbicides in soils. Herbicides and the soil (Blackwell Sci. Publications, Oxford), pp. 1-19. 1960. Bartley, C. E. Triazine compounds. Farm Chem. 122:28-34. 1959. Bayer, D. E. and K. P. Buchholtz. The influence of pre-emergence treatments with simazine and several isomers in yields of c o m and control of weeds. North Central Weed Control Conf. Research Report 14:86-87. 1957. Behrens, R. Relative residual phytotoxicity of simazine and 2-chloro-4-ethylamino-6-isopropylamino-jj-triazine (atrazine). Proc. of North Central Weed Control Conf. 16:101. 1959. ______and R. L. Thompson. Effect of simazine carry-over on oat yields. Proc. of North Central Weed Control Conf. 17:90. 1960. Bondarenko, D. D. Decomposition of amitrol in soil. Proc. of North Central Weed Control Conf. 15:5-6. 1958. ______. 3-amino-1,2,4-triazole as an herbicide on Canada thistle [Cirsium arvense (L.) Scop.] and its effect on soil microor ganisms. Ph.D. dissertation. The Ohio State University. 1957. 74 14. . Simazine on soybeans, navy beans, pinto beans and sugar beets. Proc. of North Central Weed Control Conf. 15:110. 1958. 15* ______an(* C. Dowler. Herbicides on com. Proc. of North Central Weed Control Conf. 15:107. 1958. 16. ______, R. E. Ascheman and E. W. Stroube. Herbicides on com. Proc. of North Central Weed Control Conf. 17:86. 1960. 17. Brown, D. A. Herbicides for control of weeds in field com. Proc. of North Central Weed Control Conf. 15:107. 1958. 18. Brown, J. W. and J. W. Mitchell. Inactivation of 2,4-dichloro phenoxyacetic acid in soil as affected by soil moisture, temper ature, the addition of manure and autoclaving. Bot. Gaz. 109:314-323. 1948. 19. Buchholtz, K. P. Responses of oats to residual triazine herbicides in the soil. Proc. of North Central Weed Control Conf. 16:87. 1959. 20. Burnside, 0. C. and R. Behrens. Phytotoxicity of simazine. Weeds 9:145-157. 1961. 21. Burschel, P. and V. H. Freed. The decomposition of herbicides in soils. Weeds 7:157-161. 1959. 22. Chadwick, L. C. Germination and growth of oats seeded in simazine treated soil. Proc. of North Central Weed Control Conf. 17:50-51. 1960. 23. Chandra, P., W. R. Furtick and W. B. Ballen. The effects of four herbicides on microorganisms in nine Oregon soils. Weeds 8:589-598. 1960. 24. Chaplin, D. and E. K. Alban. Varietal response of sweet c o m to simazine. Proc. of North Central Weed Control Conf. 17:52. 1960. 25. Crafts, A. S. Toxicity of certain herbicides in soils. Hilgardia 16:459-483. 1945. 26. . Toxicity of 2,4-D in California soils. Hilgardia 19:141-158. 1949. 27. Danielson, L. L. Evaluation of simazine for control of weeds in sweet com. Proc. of Southern Weed Conf. 12:88. 1959. 28. Davis, D. E., H. H. Funderburk, Jr. and N. G. Sansing. Absorption, translocation, degradation and volatilization of radioactive simazine. Proc. of Southern Weed Conf. 12:172-173. 1959. 75 29. ______, ______a n d ______. The absorption and translocation ofC-£4-labeled simazine by corn, cotton and cucumber. Weeds 7:300-309. 1959. 30. Davis, F. L. and F. L. Selman. Effects of water upon the movement of dinitro weed killers in soils. Weeds 3:11-20. 1954. 31. DeRose, H. R. and A. S. Newman. The comparison of the persistence of certain plant growth-regulators when applied to the soil. Proc. Soil Sci. Soc. Amer. 12:222-226. 1947. 32. Derscheid, L. A. Dalapon, amitrol, atrazine and zytron applied post-emergence for control of foxtails in corn. Proc. of North Central Weed Control Conf. 16:17. 1959. 33. ______. Granular CDAA, simazine, EPTC, fenac, amoben and zytron applied pre-emergence for controlling foxtails in com. Proc. of North Central Weed Control Conf. 16:79. 1959. 34. Egley, G. H., D. J. Moore and B. J. Rogers. Persistence of chemi cal weed control in corn in high rainfall seasons. Proc. of North Central Weed Control Conf. 15:107-108. 1958. 35. ______, E. E. Schweizer and B. J. Rogers. Pre- and post-emer gence weed control in c o m on muck. Proc. of North Central Weed Control Conf. 16:82. 1959. 36. Fletcher, W. W. The effects of herbicides on soil microorganisms. Herbicides and the soil (Blackwell Sci. Publications, Oxford), pp. 20-62. 1960. 37. Fletchall, 0. H. The effects on subsequent crops of simazin treat ments on corn. Abs. Weed Soc. Amer., pp. 2-3. 1958. 38. Freeman, J. F. Control of weeds in corn with herbicides used pre emergence. Proc. of North Central Weed Control Conf. 16:82. 1959. 39. ______. Control of weeds in c o m with herbicides used pre emergence. Proc. of North Central Weed Control Conf. 17:86. 1960. 40. ______. Pre-emergence control of weeds in corn with herbicides. Proc. of North Central Weed Control Conf. 15:108. 1958. 41. Friesen, G. Effect of several pre-emergence herbicides for weed control in com. Proc. of North Central Weed Control Conf. 15:100. 1958. 42. Guillemat, M. J. Microbiologie vegetale-interactions entre la simazine et la mycoflore du sol. Comptes rendus des seances de l'Academie des Sciences. 250:1343-1344. 1960. 76 43. Hale, M. G., F. H. Hulcher and W. E. Chappell. The effects of several herbicides on nitrification in a field soil under labor atory conditions. Weeds 5:331-341. 1957. 44. Harper, H. J. The use of sodium chlorate in the control of Johnson grass. Jour. Amer. Soc. Agron. 22:417-422. 1930. 45. Heck. A. F. A method for the determination of total carbon and also for the estimation of carbon dioxide evolved from soils. Soil Sci. 28:225-229. 1929. 46. Hernandez, T. P. and G. F. Warren. Some factors affecting the rate of inactivation and leaching of 2,4-D in different soils. Proc. Amer. Soc. Hort. Sci. 56:287-293. 1950. 47. Hill, G. D., J. W. McGahen, H. M. Baker, D. W. Finnerty, and C. W. Bingeman. The fate of substituted urea herbicides in agricul tural soils. Agron. Jour. 47:93-104. 1955. 48. Holstuu, J. T., Jr. and W. E. Loomis. Leaching and decomposition of 2,2-dichloropropionic acid in several Iowa soils. Weeds 4:205-217. 1956. 49. Jones, H. E. Influence of 2,4-dichlorophenoxyacetic acid on nitrate formation in a prairie soil. Jour. Amer. Soc. Agron. 40:522-526. 1948. 50. Koike, H. and P. L. Gainey. Effects of 2,4-D and CADE, singly and in combination, upon nitrate and bacterial content of soils. Soil Sci. 74:165-172. 1952. -1. Kratochvil, D. E. Determinations of the effect of herbicides on soil micro-organisms. Weeds 1:25-31. 1951. 52. Levi, E. and A. S. Crafts. Toxicity of maleic hydrazide in California soils. Hilgardia 21:431-463. 1952. 53. ______a n d ______. Toxicity of phenyl mercuric compounds in California soils. Hilgardia 21:465-485. 1952. 54. Loustalot, A. J., T. J. Muzik and H. J. Cruzado. A study of the persistence of CMU in soil. Agri. Chem. 8:52-53, 97-101. 1953. 55. Magee, L. A. and A. R. Colmer. Some effects of 2,4-dichloro phenoxyacetic acid upon Azotobacter as measured by respiration inhibition. Weeds 4:124-130. 1956. 56. Meggitt, W. F. Weed control in corn with spray and granular formulations of herbicides. Proc. of North Central Weed Control Conf. 17:87. 1960. 77 57. ______and J. C. Anderson. An evaluation of pre-emergence herbicides in field corn and the reaction of several inbred lines to the herbicides. Proc. of North Eastern Weed Control Conf. 13:110-114. 1959. 58. Montgomery, M. and V. H. Freed. A comparison of the leaching behavior of simazine and atrazine in Cheholis sandy loam. Western Weed Control Conf. Res. Prog. Rept., p. 79. 1959. 59. ______a n d ______. The uptake, translocation and metabolism of simazine and atrazine by corn plants. Weeds 9:231-237. 1961. 60. ______a n d ______. The uptake and metabolism of simazine and atrazine by c o m plants. Western Weed Control Conf. Res. Prog. Rept., pp. 93-94. 1959. 61. Moreland, D. E., W. A. Gentner, J. L. Hilton and K. L. Hill. Studies on the mechanism of herbicidal action of 2-chloro-4, 6 -bis (ethylamino)-£-triazine. Plant Phy. 34:432-435. 1959. 62. Newman, A. S. The effect of certain plant growth-regulators on soil microorganisms and microbial processes. Proc. Soil Sci. Soc. Amer. 12:217-221. 1947. 63. ______and C. R. Downing. Herbicides and the soil. Jour, of Agri. and Food Chemistry. 6:352-353. 1958. 64. ______, H. R. DeRose and H. T. DeRigo. Persistence of isopropyl N-phenylcarbamate in soils. Soil Sci. 66:393-397. 1948. 65. ______and J. R. Thomas. Decomposition of 2,4-dichlorophenoxy- acetic acid in soil and liquid media. Proc. Soil Sci. Soc. Amer. 14:160-164. 1949. 66. ______, ______and R. L. Walker. Disappearance of 2,4- dichlorophenoxyacetic acid and 2,4,5-trichlorophenoxyacetic acid from soil. Proc. Soil Sci. Soc. Amer. 16:21-24. 1952. 67. Ogle, R. E. and G. F. Warren. Fate and activity of herbicides in soils. Weeds 3:257-273. 1954. 68. Ragab, M.T.H. and J. P. McCollum. Degradation of C^-labeled simazine by plants and soil microorganisms. Weeds 9:72-84. 1961. 69. Reid, J. J. Most herbicides disappear rapidly from the soil. Crops and soils 12:19. 1960. 70. Richards, R. F. Recent results of simazine and related triazines for selective weed control. Proc. of Southern Weed Conf. 12:207-212. 1959. 78 71.______. Simazine and related triazines - a progress report. Abs. Weed Soc. Amer., p. 9. 1958. 72. Robinson, E. L. The relation of 2,4-dichlorophenoxyacetic acid to pH and organic matter of soils. Ph.D.dissertation. The Ohio State University. 1956. 73. Rogers, B. J. GET (Simazine) for annual weed control in c o m in- breds. North Central Weed Control Conf. Res. Rept. 14:37. 1957. 74. Rosenfels, R. S. and A. S. Crafts. Chlorate Distribution and the effect of nitrate concentration on chlorate toxicity in soil columns. Hilgardia 14:71-79. 1941. 75. Roth, M. W. Etude comparee de la reaction du Mais et du Bli a la simazin, substance herbicide. Comptes rendus des seances de l'Academie des Sciences. 245:942-944. 1957. 76. Schneider, E. 0. Comparison of simazine and atrazine for weed con trol in com. Proc. of North Central Weed Control Conf. 16: 52-53. 1959. 77. ______. Simazine and related triazine herbicides. Proc. of North Central Weed Control Conf. 15:10-11. 1958. 78. Scudder, W. T. Persistence of simazine residues in two central Florida soils. Proc. of Southern Weed Conf. 12:187. 1959. 79. Sexsmith, J. J. Effectiveness of four herbicides applied as pre planting treatments for control of weeds in sweet com. Proc. of North Central Weed Control Gonf. 17:87. 1960. 80. Shear, G. M. Weed control in c o m during 1957-1958. Proc. of Southern Weed Conf. 12:12-16. 1959. 81. Sheets, T. J. The comparative toxicities of monuron and simazine in soil. Weeds 7:189-194. 1959. 82. ______. Uptake and distribution of simazine by oat and cotton seedlings. Weeds 9:1-13. 1961. 83. ______and L. L. Danielson. Herbicides in soils. ARS, USDA publication 20-9:170-181. 1960. 84. Sherburne, H. R. and V. H. Freed. Adsorption of 3-(jg-chlorophenyl)- 1,1-dimethylurea as a function of soil constituents. Jour, of Agri. and Food Chem. 2:937-939. 1954. 85. Smith, N. R., V. T. Dawson and H. E. Wenzel. The effect of certain herbicides on soil microorganisms. Proc. Soil Sci. Soc. Amer. 10:197-201. 1946. 79 8 6 . Stroube, E. W. and D. D. Bondarenko. Herbicides on com. Proc. of North Central Weed Control Conf. 16:83. 1959. 87. Sund, K. A. Residual activity of 3-amino-l,2,4-triazole in soils. Jour. Agri. and Food Chem. 4:57-60. 1956. 8 8 . Switzer, C. M. Observations in 1958 on plots treated with simazine and monuron in 1957. Proc. of North Central Weed Control Conf. 15:128. 1958. 89. ______and W. E. Ranser. Most herbicides disappear rapidly from the soil. Crops and Soils 12:19. 1960. 90. Teater, R. W. The effects of certain herbicides on nitrification and on carbon dioxide evolution in the soil. M.S. thesis. The Ohio State University. 1955. 91. ______, J. L. Mortensen and P. F. Pratt. Effects of certain herbicides on rate of nitrification and carbon dioxide evolution in soil. Agr. and Food Chem. 6:214. 1958. 92. Thiegs, B. J. The stability of dalapon in soils. Down to Earth 11:2-4. 1955. 93. Upchurch, R. P. and W. C. Pierce. The leaching of monuron from Lakeland sand soil. Part 1. The effect of amount, intensity and frequency of simulated rainfall. Weeds 5:321-330. 1957. 94. ______a n d ______. The leaching of monuron from Lakeland sand soil. Part II. The effect of soil temperature, organic matter, soil moisture and amount of herbicide. Weeds 6:24-33. 1958. 95. Weldon, L. W. and F. L. Timmons. Penetration and persistence of diuron in soil. Weeds 9:195-203. 1961. 96. Williams, J. L. and 0. C. Lee. Performance of pre-emergence herb icides on c o m 1960. Proc. of North Central Weed Control Conf. 17:49-50. 1960. 97. Worsham, A. D. and J. Giddens. Some effects of 2,2-dichloropro- pionic acid on soil microorganisms. Weeds 5:316-320. 1957. 98. Worth, W. A., Jr. and A. M. McCabe. Differential effects of 2,4-D on aerobic, anaerobic and facultative anaerobic microorganisms. Science 108:16-18. 1948. 99. Young, H. C. and J. C. Carroll. The decomposition of pentachloro- phenol when applied as a residual pre-emergence herbicide. Agron. Jour. 43:504-507. 1951. 80 100. Zinter, C. C., C. R. Amstrup and A. J. Slough. Pre- and post emergence applications of simazine at Halstad. Proc. of North Central Weed Control Conf. 15:108-109. 1958. APPENDIX Table 18. Analysis of variance for yield of corn treated pre-emergence with simazine on May 25, 1959. Source of variation df ss ms "F" ratio Total 15 316.98 Kates 3 50.54 16.85 0.599NS Replications 3 12.14 4.05 0.144NS Error 9 254.30 28.14 81 82 Table 19. Analysis of variance for yields of corn, wheat, barley, oats and soybeans. Source of variation df ss ms "F" ratio Corn Total 15 1,369.3 Rates 3 56.5 18.8 0.31NS Replications 3 774.2 258.1 4.31* Error 9 539.7 59.9 Wheat Total 15 6,551.8 Rates 3 6,085.6 2,028.5 64.95** Replications 3 185.2 61.7 1.98NS Error 9 281.0 31.2 Barley Total 15 14,765.2 Rates 3 12,024.1 4,008.0 35.93** Replications 3 1,737.2 579.1 5.19* Error 9 1,003.9 111.5 Oats Total 15 19,767.3 Rates 3 18,084.0 6,028.0 61.26** Replications 3 797.7 265,9 2.70NS Error 9 885.6 98.4 Soybeans Total 15 2,020.5 Rates 3 1,581.6 527.2 13.01** Replications 3 74.1 24.7 0.61NS Error 9 364.8 40.5 *Significant at the 5 per cent level. **Significant at the 1 per cent level. 83 Table 20. Analysis of variance for weight of first crop of oats grown in simazine treated soil taken from field plots on October 15, 1959. Source of variation df ss ms "F" ratio Total 35 291.29 Simazine rates 3 72.10 24.03 82.86** Soil levels 2 150.71 75.36 259.86** Simazine x soil levels 6 61.50 10.25 35.35** Error 24 6.98 0.29 **Significant at the 1 per cent level. Table 21. Analysis of variance for weight of second crop of oats grown in simazine treated soil taken from field plots on October 15, 1959. Source of variation df ss ms "F" ratio Total 35 330.66 Simazine rates 3 89.06 29.69 148.45** Soil levels 2 164.73 82.37 411.85** Simazine x soil levels 6 72.19 12.03 60.15** Error 24 4.68 0.2 0 **Significant at the 1 per cent level. 84 Table 22. Analysis of variance for weight of first crop of oats grown in simazine treated soil taken from field plots on May 12, 1960. Source of variation df ss ms "F" ratio Total 35 209.33 Simazine rates 3 115.07 38.36 60.89** Soil levels 2 24.47 12.24 19.43** Simazine x soil levels 6 54.61 9.10 14.44** Error 24 15.18 0.63 **Significant at the 1 per cent level. Table 23. Analysis of variance for weight of second crop of oats grown in simazine treated soil taken from field plot s on May 12 , 1960. Source of variation df ss ms "F" ratio Total 35 191.60 Simazine rates 3 10 2 . 6 8 34.23 41.24** Soil levels 2 14.64 7.32 8.82 Simazine x soil levels 6 54.47 9.08 10.93 Error 24 19.81 0.83 **Significant at the 1 per cent level. 85 Table 24. Analysis of variance for weight of first crop of oats grown in simazine treated soil taken from field plots on October 10, 1960. Source of variation df ss ms "F" ratio Total 35 12.54 Simazine rates 3 4.27 1.42 7.89** Soil levels 2 0.91 0.46 2.56NS Simazine x soil levels 6 2.93 0.49 2.72* Error 24 4.43 0.18 *Significant at the 5 per cent level. **Significant at the 1 per cent level. Table 25. Analysis of variance for weight of second crop of oats grown in simazine treated soil taken from field plots on October 10, 1960. Source of variation df ss ms "F" ratio Total 35 15.51 Simazine rates 3 2.78 0.93 2.27NS Soil levels 2 0.19 0.10 0.24NS Simazine x soil levels 6 2.75 0.46 1.12NS Error 24 9.79 0.41 86 Table 26. Analysis of variance for weight of oat seedlings grown on soil treated with atrazine and simazine which were leached with varying amounts of water applied to the soil surface. Source of variation df ss ms "F" ratio Total 359 807.097 Herbicide treatment 2 180.949 90.475 999.41** Soil type 1 1.860 1.860 20.44** Herbicide treatment x soil type 2 0.683 0.319 3.51* Water rate 3 166.536 55.512 610.02** Water rate x herbicide treatment 6 88.106 14.684 16.14** Water rate x soil type 3 1.041 0.347 3.81* Water rate x soil type x herbicide treatment 6 0.848 0.141 1.55NS Soil level 4 163.536 40.884 449.27** Soil level x herbicide treatment 8 89.100 11.138 122.36** Soil level x soil type 4 4.642 1.161 12.76** Soil level x water rate 12 55.349 4.612 50.68** Soil level x herbicide treatment x soil type 8 2.195 0.274 3.01** Soil level x herbicide treatment x water rate 24 25.495 1.062 11.67** Soil level x soil type x water rate 12 2.727 0.227 2.49** Soil level x soil type x water rate x herbicide treatment 24 2.238 0.093 1.02NS Error 240 21.837 0.091 *Significant at the 5 per cent level. **Significant at the 1 per cent level. 87 Table 27. Analysis of variance for the amount of carbon, evolved as carbon dioxide, from 100 grams of non-treated and simazine treated soil, Source of variation df ss ms ,tFn ratio Total 63 10,044.700 Treatments 1 4.516 4.516 0.028NS Dates of collection 7 1,535.362 219.337 1.358NS Treatments x dates 7 750.232 107.176 0 . 633NS Error 48 7,754.590 161.554 AUTOBIOGRAPHY I, Edward W. Stroube, was born in Christian County, Kentucky, on April 2, 1927, and received my elementary and high school education in the public schools of that county. Upon completing high school in 1945, I was engaged in farming for three years. I entered the College of Agriculture and Home Economics at the University of Kentucky in January 1948, and received a B.S. degree in Agriculture in January 1951. I entered the United States Air Force in March 1951, where I attended the Air Force Officer Candidate School and received a commission of Second Lieutenant. After being discharged from the Air Force in July 1954, I was Assistant and Associate County Agricultural Agent in Bourbon County, Kentucky, for three years. I entered the University of Kentucky Graduate School in September 1957, and received an M.S. degree in Agronomy in 1958. I entered The Ohio State University Graduate School in September 1958 and held the positions of Research Assistant, Assistant Instructor and Instructor while completing the requirements for the Doctor of Philosophy degree. 88