MSU RETURNING MATEEILWLE: PIace in book drop to w your r‘e(j0r‘d_ {”3 mm ‘v be charged if beak is returned after the date stamped below. EFFECTS OF ATRAZINE RESIDUE ON SOYBE‘AN (GLYCINE MAX (L.) MERR.) GROWTH UNDER THREE TILLAGE SYSTEMS AND VARIOUS HERBICIDES BY John Andrew Pawlak A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTERS OF SCIENCE Department of Crop and Soil Sciences 1985 H ,. .‘ .1 a .- ( ' - ' . .. ,3 I ' J "‘-/‘/ \;:I' C} It“; {i .12 \J @ Copyright by John A. Pawlak 1985 ii ABSTRACT EFFECTS OF ATRAZINE RESIDUE ON SOYBEAN (GLYCINE MAX (L.) MERR.) GROWTH UNDER THREE TILLAGE SYSTEMS AND VARIOUS HERBICIDES. BY John Andrew Pawlak Field experiments were initiated in the fall of 1982 to examine the effects of tillage on degradation of atrazine (Z-chloro-4- (ethylamino)-6-(isopropylamino)-§-triazine in soil. Interactions of atrazine residue with two soybean varieties and six soil applied preemergence herbicide treatments were also examined. Parameters used in evaluation included visual ratings of soybean injury and soybean yield. Soil samples were analyzed fOr atrazine using Soxhlet extraction and quantified by gas chromatography. Injury ratings at growth stage V4 indicated minimum tillage resulted in greater atrazine injury thanlmoldboard plowing. Metribuzin (4-amino-6-tert-butyl-3-(methylthio)gas-triazin-S(4H)-one) reacted synergistically with atrazine under chisel plowing. This may have been due to the disturbed crop residue layer which allowed the metribuzin to reach the rooting zone and the atrazine residue, which renained in the rooting zone under the chisel plowed system. Tillage had no effect on atrazine distribution between the 0 to S and the 5 to 15 cm depths. Percent unextractable atrazine was greater with higher application rates. ACKNONLEIISEMENTS I am deeply indebted to Dr. James J. Kells for his help in conducting this research and in the preparation of this manuscript. I am also thankful for his friendship and valuable counsel. My appreciation is extended to Dr.£Nilliam F. Meggitt for serving as my major advisor and to Dr. Donald Penner and Dr. Richard Leavitt for their assistance while serving on my guidance committee. I would also like to thank Dennis Cosgrove, Paul Horny, Geoffery List, Dale Mutch, Frank Roggenbuch, Karen Renner, Gary Powell, Veldon Sorenson and Jerry Wilhm for their friendship and assistance in the course of this project. Special thanks goes to Jackie Schartzer for her patient clerical efforts in the preparation of this manuscript. To my parents, John and Evelyn, for all their love and support throughout the course of this project. 1'v TABLE OF CONTENTS LI ST OF TABLES O O O O O O O O O O O O O O O 0 LIST OF FIGL’RES O O O O O O O O O O O O O O O INmecrIm O O O O O O O O O O O O O O O O 0 CHAPTER 1 LITERATURE REVIEW . . . . . . . . I NTROWCI‘I m 0 O O O O O O O 0 Effect of tillage on atrazine dispersion . Atrazine degradation . . . . Atrazine-Metribuzin Interactions . . . . . Varietal Responses . . . . . LITERATURE CITED . . . . . . . FACTORS EFFECTING SOYBEAN RESPONSE TO ATRAZINE RESIDUE . . . . . . . . . . . . . ABSTRACT . . . . . . . . . . . INTRODUCTION . . . . . . . . . MATERIALS AND METHODS. . . . . RESULTS AND DISCUSSION . . . . LITERATURE CITED . . . . . . . THE EFFECT OF TILLAGE ON ATRAZINE AND DISTRIBUTION. . . . . . . . . AB STRACT O O O O O O O O O O O I N mowCT I m C O O O O O O O 0 MATERIALS AND METHODS. . . . . DISAPPEARANCE PAGE vii ix H NOCDNH NH 36 36 38 4O 42 74 78 78 79 82 CHAPTER APPENDIX (Continued) RESULTS AND DISCUSSION. LITERATURE CITED. . . . SUMMARY AND CONCLUSIONS. . vi PAGE 84 100 104 106 Chapter 2 Table Table Table Table Table 3. LIST OF TABLES The effect of tillage on varietal differences in soybean yield averaged over atrazine treamnts. O O O O O O O O O O O O O O O O O O Varietal response, in terms of injury, to atrazine residue under chisel plowing. . . . Varietal response, in terms of injury, to soybean herbicides under three tillage systems systems at growth stage V4. . . . . . . . . . . The effect of soybean herbicides on injury with increasing atrazine rates at growth stage V4. . The effect of tillage system on soybean yield . vii PAGE 43 44 46 48 71 PAGE Chapter 3 Table l. The effect of tillage on atrazine disappearance at 2 rates 133 days after application . . . . . . 86 Table 2. The effect of tillage on atrazine disappearance at 2 rates 350 days after application . . . . . . 87 viii Chapter 2 (continued) Figure 5. Figure 6. Figure 7. Figure 8. Soybean injury in 1984, under no-tillage, following atrazine application in 1983. Metribuzin (MET), chloramben (CHL), or linuron (LIN), were applied in 1984, or no application was made (UNT). . . . . . . . . Soybean injury in 1984, under no-tillage (NT), chisel plowed (CH), and moldboard plowed (MB), following atrazine application in 1983. Chloramben was applied preemergence in 1984. . . . . . . . . . . . Soybean injury in 1984, under no-tillage (NT), chisel plowed (CH), and moldboard plowed (MB), following atrazine application in 1983. Linuron was applied preemergence in 1984 O O O I O O O O O O O O O ..... Soybean injury in 1984, under moldboard plowing, following atrazine application in 1983. Metribuzin (MET), chloramben (CHL), or linuron (LIN), were applied in 1984, or no application was made (UNT) . . . . . . . PAGE 0 O O 58 C O O 61 O O O 63 O O O 65 PAGE Chapter 3 (continued) Figure 5. Atrazine extracted, from a 2.24 kg/ha application rate, in the spring of 1983 (S- 83) immediately after application, in the fall of 1983 (F-83) 133 days after application, and in the spring of 1984 (S- 84) 350 days after application and after fall-tillage, from the 0 to S cm soil profile, under three tillage systems, no— tillage (NT), chisel plowed (CH), and mldma rd plowed (MB) 0 O O O O O O O O O O O O C 97 Figure 6. Atrazine extracted, from a 2.24 kg/ha application rate, in the spring of 1983 (S- 83) immediately after application, in the fall of 1983 (F-83) 133 days after application, and in the spring of 1984 (S- 84) 350 days after application and after fall-tillage, from the 5 to 15 cm soil profile, under three tillage systems, no- tillage (NT), chisel plowed (CH), and moldboard plowed (MB). . . . . . . . . . . . . . 99 xiv I NTRODUCT I ON Atrazine is commonly used in corn and sorghum for control of grass and broadleaf weeds throughout the midwestern corn belt. However, under conditions of low moisture, low temperature, high pH, a textured soil, and high application rates, atrazine may persist into the next growing season. This poses a problem if atrazine sensitive crops, such as soybeans, are to be planted the year after atrazine application. Factors such as tillage, soybean herbicides, and soybean planting practices may be manipulated to reduce possible soybean injury. It is the objective of this thesis to examine these factors. XV CHAPTER 1 LITERATURE REVIEW INTRODUCTION Atrazine [2—chloro-4-(ethy1amino)-6-(isopropy1amino)-§_-triazine] has been effectively used for control of several weeds including common lambsquarter (Chenopodium album L.), eastern black nightshade (Solanum ptycanthum Dun.), common ragweed (Ambrosia artemisiifolia L.), and wild mustard (Brassica kaber (DC.) Wheeler), since its development by J. R. Geigy in the mid 1950's (42). Atrazine is commonly used throughout the corn belt of the United States, due to its relatively low cost and high effectiveness. However, the use of atrazine does pose some problems. Recommended rates of atrazine may persist in the soil into the next growing season, causing injury to sensitive crops planted that year. Such crops include oats (Avena sativa L.), seedling alfalfa (Medicago sativa L.), and soybeans (Glecine max (L.) Merr.) (12). Tillage may influence the carryover of atrazine in soil by burying or diluting the residue (6). Along with mixing the soil, tillage or lack of tillage may influence the soil surface in terms of the amount of plant residue remaining (63). This residue layer may interfere with herbicide distribution on the soil (20) and may aid in moisture conservation (10). Tillage systems also influence the pH of the soil 2 surface by determining if pH altering materials, such as lime or nitrogen fertilizers, can be incorporated (11). The amount of atrazine remaining in the soil also influences crop response. Atrazine persistence is influenced by chemical and microbial degradation, both of which are influenced by temperature, moisture, and light. Soil type also influences herbicide breakdown and is one of the factors regulating how much of the herbicide residue is actually available for plant uptake (16). Metr ibuz in (4~amino-6-tert-butyl-3-(methy1 thio)-§_s_-triaz in—S (4H) - one) used on atrazine sensitive crops, such as soybeans, the year following atrazine application may interact with the atrazine residue resulting in increased crop injury (44). Soybean varieties vary in response to metribuzin (54). This may play a part in reducing potential yield reductions due to atrazine residue and metribuzin application with certain varieties. Seed size and seeding rate have also been reported to reduce yield losses due to atrazine residue (1, 2, 30). EFFECT OF TILLAGE (N ATRAZINE DISPERSICN Burnside et a1. (18) found soil persistence from the subsequent year normal use rates of atrazine was only a minor problem under reduced tillage systems. Atrazine carryover was less of a problem under the reduced than conventional tillage systems in experiments conducted in Nebraska (18). Bauman and Ross (6) also found atrazine persisted longer under chisel or conventional plowing systems than under the coulter tillage system. Kells et a1. (41) found the percent of extractable atrazine decreased with time under both no—tillage and 3 conventional tillage systems, however, unextractable radioactivity was always higher under no-tillage. This indicates greater breakdown or adsorption to soil or soil constituents under the no-tillage. Plant Residue Under the no—tillage system, plant residue remains on the surface. Walker and Crawford (79) found undecayed plant material did not adsorb the triazine herbicides. Bauman and Ross (6) found that although corn residue intercepted some of the atrazine during application, 86 to 90% was removed from the corn residue 30 days after application and only 1% remained after 90 days. Plant residue did not significantly affect weed control when herbicides were applied at recommended rates, but had an increased influence on control as herbicide rates were reduced (20). Control of foxtail millet (Setaria italice (L.) Beauv.) with atrazine decreased with increasing residue levels when simulated rainfall did not occur (20). Lowder and Weber (46) found atrazine retention by crop residue appeared to be primarily a function of the total amount of rainfall, and secondly, a function of residue type and rainfall patterns. They found one 10 cm rainfall immediately after atrazine application or 7 days after application removed approximately 87 and 77% of the atrazine residue from fresh oats and dry corn residue, respectively. Slightly less atrazine was removed from the residue when four 2.5 cm rainfalls were applied in place of the one 10 cm rainfall (46) . Moisture Wicks and Smika (85) found soil moisture content to be generally greater without tillage. Blevins (10) saw higher corn yields due to more effective use of soil moisture by no-tillage as compared to conventional tillage. No-tillage treatments had a higher volumetric water content to a depth of 60 cm during most of the growing season. The greatest difference occurred in the upper 0 to 8 cm depth. The decrease in evaporation and the greater ability to store moisture under no-tillage produced a greater water reserve (10). Moschler (50) found that the more efficient use of water under the no-tillage system resulted in more efficient use of lime. This resulted in greater increases in corn yield under the no-tillage system due to lime than under conventional tillage. Associated withtthe larger yield increases from lime in the no-tillage culture were: 1) higher pH in the upper 0 to 10 cm layer (6.4 vs. 6.0); 2) a greater increase in exchangable calcium, and 3) a reduction in exchangable aluminum in the O to 10 cm layer (50). Birk and Roadhouse (9) applied atrazine to a loam soil at rates ranging from 2 to 20 1b/A. Some plots were planted to corn, others were left fallow. At the end of the first sampling season there was appreciably greater residue remaining in the corn plots than in the similarly treated fallow plots. An average of 43.8% of applied atrazine remained in the corn planted plots compared to 18.3% remaining in the fallow plots. The greater persistence was probably due to the much drier soil, which was characteristic of the corn plots during the season (9). Nitrogen Acidity also influences the persistence of atrazine in the soil. It has been shown by numerous authors that surface soil pH decreases under no—tillage compared to conventional tillage (7, ll, 22, 31, 51). Since atrazine binding and degradation increases as pH decreases, as shown by Hiltbold and Bauchaman (36), there should be reduced atrazine persistence under the no-tillage system in the surface layer of soil. Blevins (10) found that soil pH was lowered by increasing ammonium nitrate application and was lower with no—tillage than with conventional tillage. The use of NaNO3, a basic forming nitrogen fertilizer, resulted in increased atrazine efficiency and longevity as CONPGIEd t0 the use of NH4NO3, an acid forming nitrogen fertilizer during a dry year in research reported by Lowder (46). No differences were observed during a wet year. Line Liming significantly increased atrazine efficency and longevity in both no-tillage and conventional tillage systems (8, 46). Kells (41) found the addition of lime under no-tillage resulted in a significantly greater amount of applied atrazine remaining at any point in time. The same was also true under conventional tillage. Lowden (46) found that mean surface soil pH levels during the growing season were higher with no-tillage than with conventional tillage. This was due to retention of lime on the surface under no-tillage compared to mixing in the soil under conventional tillage. No increases in atrazine efficiency or longevity were found in one system over the others (46). Kells (41), using 14C labeled atrazine, found the amount 6 of unextractable radioactivity in the soil under no-tillage increased significantly over time at all levels of surface pH tested. The same was true under conventional tillage. Under no-tillage, 72% of the appl ied radioactivity remained as atrazine 14 days after application in areas receiving lime and 60% remained as atrazine where no lime was applied. Under conventional tillage 75% of the applied atrazine remained 14 days after treatment in areas receiving lime and 64% remained where no lime was applied. The effect of lime on the amount of parent atrazine present in the soil was found to be directly related to its effect on soil pH (41). Best (105) found that by liming an acid Bladen silt loam from pH 5.5 to 7.5, the phytotoxicity of atrazine and prometryn were increased. Weed Control Kells (41) found additions of lime as compared to unlimed treatments resulted in significantly increased weed control with simazine (2-chloro-4,6-bis(ethylamino)-§_-triazine) (83 vs. 63%), yield (5930 vs. 5290 kg/ha), and soil pH (5.91 vs. 5.22). Poorest weed control was observed with no-tillage on unlimed plots In studies using atrazine, higher levels of extractable triazine in the soil resulted in significantly better weed control under both no-tillage and conventional tillage. However, at any level of extractable triazine, weed control was always greater under conventional tillage. Under no— tillage 19% weed control was observed in areas where 18% of the applied atrazine remained compared with 76% weed control in areas where 52% remained as atrazine. Under conventional tillage 60% weed control was recorded in areas where 6% of the applied atrazine remained compared with 93% weed control in areas where 52% remained as atrazine (41). ‘— Triplet (75) grew continuous corn under no-tillage and conventional tillage for 7 years to evaluate several herbicides for use in both crop culture systems. The only consistently satisfactory herbicide combination for the no-tillage corn were simazine and paraquat (1,l'dimethyl-4,4'bipyridinium ion). Annual weed population shifted rapidly with different herbicide treatments; fall panicum (Panicum dichotomiiflora Michx.) was the major annual weed where triazines were used as the residual herbicide. After several years of corn growth under no-tillage, hemp dogbane (Apocynum cannibinum L.) became a significant problem in some areas. Corn yields were equal under no—tillage and conventional tillage systems provided weed control was satisfactory (75). Putnam and DeFrank (54) found cover crops such as rye (Secale cereale L.) or wheat (Triticum aestivum L.) provided excellent weed control in spring drilled peas with no need for other herbicides than that needed for burndown. The use of fall planted cover crops with no- tillage also reduced broadleaf weed population 62-85% in carrots (Davlus carrota L.) and onions (Allium sp.) on organic soil. Residue of spring planted oats, rye, wheat, sorghum (§_._ vulgare), and sorghum + sudangrass hybrids (Sorghum vulgare sudanenis) reduced weed population 55 to 95% in cucumbers (Cucumis sativus) and snap beans (Phoseolus vulgare L.). This would indicate that less herbicide may be needed for equal weed control under no-tillage when compared to conventional tillage. This is contrary to Kel ls (42) finding that conventional tillage significantly increases yields, weed control, and soil pH over no-tillage. In Putnam's work a thick crop residue level was left by the solid seeded small grains used. This may explain the better weed 8 control from this crop residue when compared to; the corn residue used 0-9-, by Kells. 4‘ ' ATRAZINE DEGRADATION ‘ - Once a pesticide is released into the environment, degradation may begin. There are two major mechanisms for atrazine degradation in the soil, microbial and chemical. Microbial Breakdo‘m Best and Weber (7) determined the pattern off-”atrazine degradation was characteristic of non-biological processes. “Talbert (72), on the other hand, believed that slow microbial decomposition was the principle process involved in the dissipation ofi'simazine and atrazine. Deactivation occurred only under conditions conducive to microbial growth and little or none occurred in frozen or sterile soil. Inactivation of simazine and atrazine applied at 2.24 kg/ha on field plots as determined by soybean and oat bioassay was most rapid when the soil environment was favorable for microbial growth (67). Skipper (68) postulated degradation by soil microorganisms might be a function of qualitative, as well as quantitative differences in the microbial population. In the soils studied by Skipper, organic matter content and microbial population did not directly relate to atrazine degradation. Microbial population, temperature, aeration, and moisture, normally vary with depth, consequently rate of atrazine breakdown will likely vary with depth. Atrazine was found to degrade two to three 9 times faster in the top soil than in the subsoil in a Sharpsburg silty clay loam and in a Keith silt loam (59). Harris (32) found atrazine residue at a 38 cm depth had 61% greater persistence than atrazine placed in the top 7.5 cm. Conditions at the surface in terms of organic matter content, temperature, and aeration, were more favorable for degradation. Roeth (59) found atrazine adsorption, microbial population, soil organic matter, and atrazine degradation decreased with increasing depth in the soil horizon. Microbial Pathways Skipper and Volk (68) found approximately ten times more 14C02 was evolved from l4C--ethyl atrazine than from l4C--isopropyl atrazine. Microbial attack appears to be predominately on the ethyl side chain of atrazine. Possible degradation pathways of the side chain components of atrazine include: 1) dealkylation of the ethyl side chain by hydroxylation of the carbon atom adjacent to the amino group or 2) dealkylation and deamination of aromatic molecules by monooxygenase. Steric hindrance may limit the availability of the isopropyl side chain to microbial attack. Sirens (66) found atrazine is converted into deethylated atrazine as a major and deisopropylated atrazine as a minor phytotoxic metabolite. Isopropyl and the ring constitutent of atrazine were subject to minimal attack. The hydroxyatrazine ring was attacked more readily than the atrazine ring as shown by Skipper and Volk (68). Skipper and Volk (68) also found evolution of 14C02 from the ethyl side chain component of atrazine varied within soil type, herbicide concentration, moisture content, and air flow rate. 10 As in most chemical and biological processes, water plays an important role; the degradation of atrazine is no exception. A six fold increase in 14C02 evolution from chain 14C—labeled atrazine occurred with an increase in moisture content from 40 to 80% of field capacity (59). A Woodburn soil at 50, 70, and 90% field capacity respired 5.5, 8.5, and 10.1% of the l4C~ethyl component in 4 weeks, respectively. The lower moisture content may reduce microbial activity, limit atrazine availability, or decrease chemical hydrolysis (68) . Chemical Hydrolysis Skipper et al. (15) reported chemical hydrolysis of the _s_- triazines to their hydroxy analogs as the major pathway of degradation in the soil, with microbial attack being of minor importance. Le Baron (45) also found chemical hydrolysis of atrazine to non-phytotoxic hydroxyatrazine to be the predominant route of detoxification of atrazine in soil. Research by Harris (31) indicates that the initial hydrolysis at the two positions of the triazine ring occurred more readily than subsequent degradation steps. Since hydroxylation is a prerequsite for enzymatic fission of the benzene ring, hydrolysis of chloro-g-triazines to hydroxy-s-triazines may also be required for cleavage of the g-triazine ring (24). Factors such as moisture, soil type, leaching, and temperature, also affect the rate of atrazine degradation. Wilson and Cole (87) found watering soil to field capacity every day increased atrazine degradation compared to watering less frequently or not at all. Sheets and Craft (62) found similar results from their work with diuron (3- 11 [3,4-dichlorophenyl]-l,l-dimethylurea) and atrazine in which both were lost more rapidly from moist rather than dry soil. Many researchers (15, 16, 31, 60, 76, 77, 78) have found herbicide carryover in forms harmful to plants was less serious in the humid regions, compared to the more arid regions of the United States. Atrazine at 2.2 kg/ha significantly reduced subsequent oat yields in central and western, but not in eastern Nebraska. This may be atributed to the higher rainfall in eastern Nebraska (16). In a study comparing atrazine degradation in central and western Nebraska, Burnside (16) found greater carryover in the drier western locations. An Anselmo silty loam was used in both locations, this indicates the greater moisture in the central region enhanced breakdown. Burnside (16) found carryover to be greater on coarse textured soils, than on fine textured soils. Soils showing the greatest to least residue were sandy loams, silt loams, and silty clay loams. Soil textures had a greater influence on herbicide carryover than climate (8). Leaching may decrease atrazine persistence in the rooting zone, by moving it out of the plant rhizosphere. Brinkman (12) found yield reductions were less in 1976 due to abundant rainfall during the later half of 1975, which leached much of the atrazine residue from the rooting zone. Conversly, substantial atrazine remained in the top soil when the 1977 crop was planted, due to the dry weather in the later half of 1976. The amount, frequency, and intensity of rainfall have been shown to be important factors in soil longevity of herbicides by both Burnside (15) and Talbert (72) in separate studies. Bauman (6) also found soil factors to affect the movement and persistence of 12 atrazine under field conditions, along with the amount and frequency of rainfall after application. Ritter (58) concluded that atrazine moves more readily in wet soil than in dry soil. Roger (60) has shown organic matter to be more important in terms of _s_-triazine leaching than solubility. Once a herbicide is leached into the lower soil profile, its dissipation is markedly reduced. Herbicide breakdown, by both biological and nonbiological means, decrease with the reduced soil temperature or increasing depth in the soil horizon (S9). Atrazine was found to degrade two to three times faster in the top soil than in the subsoil of a Sharpsburg silty clay loam and a Keith silt loam by Skipper (68). Each 10° temperature increase from 10 to 30°C caused the degradation rate to increase two to three times in these soils. Similar results were found by McCormick and Hiltbold (48). Talbert (72) found atrazine, as well as diuron, to be lost more rapidly during high temperatures, rather than low temperatures. Atrazine was found to be increasingly vol itile from soil with increasing temperatures by Kearney et a1. (39). They also showed that volitility from soil ceased with leaching. Jordan (38) showed photodecomposition to stop with leaching. Wolfe (88) found direct photolysis of the g-triazines exposed to visible light was so low that it is not likely to have environmental importance. Gast (23) was able to show losses of simazine and atrazine activity when dry surface treated soil was irradiated with ultraviolet and infrared light, losses were reduced in wet soil. The direct photolysis of s-triazine herbicides in water and alcoholic solutions at 253.7 nm resulted in the nucleophilic displacement of the R1 substitute and formation of hydroxyl and alkoxy derivatives, respectively (52). Rijte (57) found the rate of photodegradation was affected by the pH 13 of the reaction mixture. The rate of reaction increased as the pH decreased, indicating that photodegradation will increase at a lower pH. One of the primary photodegradation products was the deethylated s—triazine. Soil Clay Armstrong et a1. (1) and Harris (31) showed atrazine in contact with soil was degraded more rapidly than atrazine in aqueous solution. This would suggest that soil, or some soil constituent, catalyzed degradation.h Both attributed the increased degradation to a non- biological constituent, which catalyzed atrazine to 2-hydroxyatrazine. Crystalline clays bind herbicides via their exchange sites. These sites originate from broken bonds, isomorphic substitution, and dissociation of hydrogen ions of exposed hydroxyls (22). Broken bonds result in unsatisfied charges around the edges of silica-aluminum units. Unsatisfied charges also result from isomorphic substitutions of an ion, usually Al3+ for a lower valance ion usually 1492+ in the octahedral sheets of clay particles. The exposed oxygen of hydroxyl groups may result in unsatisfied charges if the hydrogen is removed. This, however, is unlikely due to the light association of the hydrogen to the hydro group. These unsatisfied charges may be satisfied hydroxyls with cationic herbicides, such as atrazine (5, 22, 74). Soil texture differences had a greater influence than did climatic differences across Nebraska (16). This may be due to different types and amounts of clays and/or organic matter. Weber and Coble (32) reported a reduction in microbial attack on diquat (6,7-dehydrodipyrid (1,2-:2',l'-c) pyrazinediium ion) when the herbicide was adsorbed by 14 montmorillonite. The adsorbtion of atrazine by montmorillonite in the neutral Coker clay soil may protect the atrazine molecule from microbial attack (31). Baily (4) found the surface acidity of montmorillonite to be 3 to 4 pH units lower than the suspension pH, which would result in greater adsorption of atrazine. No adsorption of atrazine was reported with kaolinite by Talbert (73). Soil Organic Matter Although certain clays may adsorb triazines, organic matter is most highly related to adsorption and/or phytotoxicity of the chloro—g- triazines (31, 49, 53, 56, 63, 69, 72). Grover (25) found by adding organic matter to a Regina heavy clay soil, that the phytotoxicity from simazine to oats was reduced. Walker and Crawford (79) extensively studied the role of organic matter in the adsorption of triazine herbicides by soils and found that undecayed plant material was not very adsorptive. Studies with mixtures of clay and organic matter by Hance (27) showed they associate in a manner which reduced the total surface availability for herbicide adsorption. He suggests that in the soil, little of the clay mineral surface will be accessible to the herbicide molecule. Talbert (73) found that increasing amounts of organic matter and/or clay in a soil, generally were associated with increased adsorption of the triazine herbicides. The availability of soil applied s—triazine herbicides generally decreases as clay and/or organic matter increases (64, 84). 15 Soil pH The adsorption of simazine by 18 soils was not correlated significantly with soil pH, but was correlated significantly with percent clay and highly significantly with organic matter and titratable acidity (l9). Kells et al. found the amount of unextractable atrazine was greatest in areas where surface pH was less than 5.0 compared with areas where the surface pH was greater than 6.5. Best and Weber (7) found more rapid hydrolysis of atrazine to hydroxyatrazine in soil of pH 5.5 than 7.4. Hiltbold and Buchanan (13) found persistence of atrazine was positively related to soil pH. They also found that the extent of the pH effect varied with soil type. The effect of pH in McLaurin sandy loam amounted to 8 to 9 days longer persistence per unit increase in pH. In a Hartsells fine sandy loam 9 to 13 day increase in persistence was found per unit increase in pH. A 29 day increase in persistence was found in a Decator clay loam (36). The pka value represents the pH level at which one-half of the species in solution is present in the ionic form. Since ionic species are more water soluble than molecular species, basic herbicides, such as atrazine, have higher solubilities at low pH levels than at neutral pH levels (80). Weber also found that the higher the basicity of a pesticide the greater it will be adsorbed by acid soil particles. Maximum adsorption was found to occur at pH levels in the vicinity of the pka value for the triazine herbicides (83). Atrazine has a pKa of 1.68, which indicates maximum adsorption will occur at a pH of around 1.68. Under more acid conditions than the pKa of the adsorbent, hydrogen cations compete with the triazine molecule for the binding site (5). Because weakly basic herbicides are protenated in acid soil systems and are ionicly adsorbed by negatively charged colloids, pH 16 exerts a strong influence over both adsorption and hydrolysis of atrazine (11, 65). Colloidal surface pH may be 3 to 4 orders of magnitude lower than the pH of the soil solution (84). The Stern theory states that as distance from the soil colloid decreases, the percent 11* ions increase. Therefore, in the soil solution near the soil colloid the concentration of Hi“ is much greater than in the overall solution. This results in a lower pH near the colloidal surface. pH is normally measured and reported from the soil solution. Atrazine adsorption and degradation occur at the colloidal surface, thus, the colloidal surface pH governs the reactions (84). Buckhanam and Hiltbolt (13) reported atrazine half-lives of 10, 20, and 30 days for various soils in Alabama. They believed the difference in half-life between soils was associated with greater influence of pH on atrazine persistence between these soils. Soil colloidal properties determine the distribution of atrazine between the adsorbed and solution phases. Degradation, in the form of chemical hydrolysis, takes place on the colloidal surface. Since lowering the pH of the soil solution lowers the acidity of the soil colloid and protonates the atrazine molecule, lowering the pH of the soil solution creates an environment conducive for the adsorption of atrazine and thus the hydrolysis to the inactive hydroxy form (13). Hance (27) found adsorption of two substituted ureas, monuron and diuron (3-(3,4-dichlorophenyl)-1,1—dimethylurea), were independent of pH or exchange capacity. The adsorption of the triazines were influenced by both factors. Hance postulated that the ureas were adsorbed by coordination complexes with exchange cations, while the 17 triazines are adsorbed by a combination of these two plus protenation and consequently ion exchange reactions. The importance of each process being determined by pH, exchangable cations, and the characteristic of the adsorbate molecule (27). In separate studies Harris (29), MoGlamery (49), and Talbert (73) found atrazine adsorption to increase with decreasing pH. Colbert (19) found adsorption of atrazine, along with other triazines, to decrease on natural and limed soils as soil pH increased. Of the colloidal fraction, organic matter has the most reactive surface. This includes humin, humic and fulvic acids. The clay fraction makes up the rest of the reactive surface (5). Stevenson (70) found that organic matter and clays are bound intimately together, probably via metal ions. Thus, there are two major adsorbing surfaces available to herbicides, the clay-metal-organic matter complex and clay alone. Nearpass found adsorption of simazine by 18 soils was not correlated significantly with pH, but was correlated significantly with percent clay and highly significantly with organic matter and titratable acidity (51). Swain (71) found dissipation rate and atrazine adsorption were both correlated with organic carbon content of the soil, which ranged from 1.43 to 0.73%. No correlation between either dissipation rate or adsorption and clay content were found even though clay content ranged from 37 to 78%. A possible explanation for this may be the type of clay present. A clay such as kaolinite would have very little adsorption capacity. The organic matter may have also masked any effect of the clay. Weber (83) found the adsorption of‘the _s_-triazines were due to the complexing of the triazine molecules with functional groups on the organic colloids and/or adsorption of _s_- 18 triazine cations by ion exchange forces. The ratio of the amount of herbicide adsorbed to the amount in equilibrium solution (Kd) for a given s—triazine and exchange remained relatively constant over a range of concentrations (73). Four factors determined the role of the chemical character of the adsorbate in the overall adsorption reaction according to Baily and White (5): 1) nature of the functional groups; 2) nature of the substituting groups; 3) position of the substituting group with respect to the functional groups, and 4) magnitude of unsaturation in the molecule. Baily et a1. (5) believes there are several factors, such as surface acidity and relative polarity of the adsorbent that determines whether there is a direct relationship between water solubility and adsorbability. There appears to be a relationship between water solubility and the extent of adsorption, but only within certain families of compounds UH. An inverse relationship occurs for the chloro series of §7triazines. The solubility of the series of compounds increases as the side chain length increases, with the exception of atrazine. Temperature also affects adsorption of the triazines. Talbert (73) found that increasing temperature and pH resulted in decreased adsorption of simazine and atrazine. Harris (29) and McGlamery (49) also found increasing temperatures caused adsorption of atrazine to decrease. ATRAZINE - METRIBUZIN INTERACTIONS Although atrazine residue alone may result in soybean injury, the addition of metribuzin in combination with atrazine residue may result in increased injury. Soil pH has an effect on the activity of both metribuzin and atrazine. The phytotoxicity of both components increase with increasing soil pH (34). Best (8) found that liming increased the 14C- concentration present in the shoots of corn (Z_e_a_ m_a_y_§_ L.), cotton (Gossypium hitsutum L.) and soybeans from soil treated with 14C ring- labeled atrazine. Increasing pH resulted in increased activity of metribuzin expressed as weed control and crop injury (43). Atrazine at 10"5 and 10"6 M concentrations in a sand culture nutrient solution during early growth of "Swift” soybean seedlings decreased l4C- metribuzin uptake and movement into 12 day-old soybean shoots (44). However, 10"7 M atrazine increased C‘14 metribuzin in the shoots by increasing stomatal aperture and subsequent transpiration. Conditions favoring the synergistic interactions were low atrazine levels, which increased soybean transpiration, high metribuzin rates, and high soil pH levels (44). Atrazine applied in nutrient solution to corn, cotton, and soybeans reduced transpiration both in intact plants and excised shoots. This effect occurs only in the light. Microscopic examination revealed that atrazine caused closure of the stomates (86). Smith and Buchholtz (69) also found atrazine to reduce transpiration and stomatal aperature at concentrations of 10‘"6 molar and above. Sheet (64) showed 19 20 a close correlation between herbicide uptake and the amount of water transpired (64). Transpiration rates in darkness were positively correlated with stomatal aperture. Stomatal closure after treatment with atrazine at high concentrations or opening under sub-lethal levels of atrazine appeared to result from fluctuating C02 levels in the guard cells and substomatal cavities. This resulted from atrazine inhibiting C02 fixation in the chloroplasts (62, 86). Ladlie et a1. (44) found that atrazine at 10"6 M reduced transpiration and stomatal aperture. However, atrazine concentration of 10'7 and 10'8 M increased stomatal aperture over the control and uptake and translocation of 10-5 M l4C-metribuzin was dependent on the atrazine concentration. Stomatal opening or closing would appear to be a result of atrazine concentration and environmental conditions in a field situation. Stomatal closure due to atrazine was confirmed by Wills (26), who found that atrazine caused transpiration reduction, stomatal closure, and an initial increase in the water content of cotton. Imbamba (37) found that atrazine did not cause stomatal closure in COT—free air. Because atrazine blocks the Hill reaction from occurring (2 H20 4H + 02 + 4e"). No reducing power is available to convert C02 into glucose. Therefore, (:02 levels build up from respiration, which in turn causes the C02 sensitive guard cells to close. This then results in reduced transpiration (37). A synergistic interaction occurred with 0.07 and 0.28 kg/ha atrazine and 0.56 kg/ha metribuzin (44). Soybean growth was stimulated with 0.07 kg/ha of atrazine. Atrazine rates of above 0.28 kg/ha appeared to overload the system, and the interaction was more additive than synergistic. Higher rates of metribuzin of 0.56 and 0.84 kg/ha were needed to show synergistic effects with atrazine at 0.28 kg/ha 21 (44). Atrazine at 0.14 kg/ha and metribuzin at 0.56 kg/ha applied under field conditions intersected synergisticly'to reduce soybean growth. In the greenhouse a number of combinations with atrazine at (L07 kg/ha or greater and metribuzin and CL56 kg/ha and greater interacted synergisticly to reduce soybean fresh and dry weight 30 days after planting (44). Over a soil pH range of 4.6, 5.6, and 6.7 atrazine-metribuzin interactions were more apparent as the soil pH increased (44). Soybean plants grown in culture solutions containing various atrazine concentrations showed increased or decreased 14C—metribuzin uptake and plant transpiration, depending on the concentration of atrazine used in the preconditioning solution. Greater 14C-metribuzin moved into the shoot and transpiration increased over the control at 10"7 M concentration of atrazine. Atrazine concentrations of 10"5 and 10‘6 M inhibited transpiration and net uptake. Ladlie et al. (44) concluded the basis for the interaction was the effect of atrazine on the transpiration of the soybean plant and the associated increase or decrease in uptake of metribuzin. Synergistic interactions occurred when atrazine at subtoxic levels increased stomatal opening and increased transpiration, resulting in increased metribuzin uptake. The interaction was most apparent at high soil pH levels. An additive interaction appeared to result from higher concentrations of atrazine, which caused a reduction in transpiration (44). Uptake and translocation of root fed atrazine increased as temperature increased. Greater uptake and translocation of atrazine occurred under low rather than high relative humidity (81). VARIETAL RESPG‘JSES Researchers have found ways to reduce triazine injury to sensitive crops grown in atrazine treated soils. Hardcastle (28) found metribuzin by variety interactions existed as indicated by soybean stand height and yield reduction. Oplinger (55) showed tolerant varieties such as A78—123018, had minimal leaf kill of 3% when 3/4 lb/A of metribuzin was applied. Sensitive varieties, such as NK-l884, resulted in 55% leaf kill at the same rate. Average leaf kill for all varieties tested equalled 17%. Brinkman and Harvey (12) found differences in oat cultivars in tolerance to atrazine residue, but differences were not great enough to justify development of tolerant varieties. Anderson (1) measured soybean varietal tolerance to atrazine by recording the percent reduction in dry weight compared to each varieties untreated check. Tolerance thus measured generally increased as seed size increased. Regression analysis indicated that 80% of the variation in response was attributed to variation in seed size. One possible explanation of these results may be that as atrazine was gradually dissipated during the test, the large seeded strains survived on food reserved in the cotyledons until concentrations reached a non- lethal level. The small-seeded strains may not have had enough reserves to survive until a non-lethal level was reached. Another explanation may be the larger seedling produced by larger seeds may 22 23 have had a smaller absorbing surface related to the total seedling volume than did seedlings produced by small seeds. Anderson also found that increasing soybean seeding rates 1.5 to 2.0 times can compensate for losses of yield that would be caused from atrazine carryover or excess metribuzin application (2). LITERATURE CITED Anderson, R. N. 1969. Influence of soybean seed size on response to atrazine. Weed Sci. 18:162-164. Anderson, R. N. 1981. Increasing herbicide tolerance of soybeans by increasing seeding rates. Weed Sci. 29:336-338. Armstrong, D. E., C. Chester, and R. F. Harris. 1967. Atrazine hydrolysis in soil. Soil Sci. Soc. Am. Proc. 31:61-66. Bailey, G. W., J. L. White, and T. Roghberg. 1968. Adsorption of organic herbicides by montmorillonite: Rage of pH and chemical character of adsorbate. Soil Sci. Soc. Amer. Proc. 32:222-234. Bailey, G. W. and J. L. White. 1970. Factors influencing the adsorption, desorption, and movement of pesticides in soil. Residue Review. 32:29-92. Springer-verlag. Bauman, T. T. and M. A. Ross. 1983. Effect of three tillage systems on the persistence of atrazine. Weed Sci. 31:423-426. 24 lo. 11. 12. 13. 25 Best, J. A. and J. B. Weber. 1974. Disappearance of s-triazines as affected by soil pH using a balance-sheet approach. Weed Sci. 22: 364-373. Best, J. A., J. B. Weber, and T. J. Monaco. 1975. Influence of soil pH on s-triazine availability to plants. Weed Sci. 23:378- 382 . Birk, L. A. and F. E. B. Roadhouse. 1964. Penetration of and persistence in soil of the herbicide atrazine. Can. J. Plant Sci. 44: 21-27 . Blevins, R. L., D. Cook, 8. H. Phillips, and R. E. Phillips. 1971. Influence of no-tillage on soil moisture. Agron. J. 63:593-596. Blevins, R. L., G. W. Thomas, and P. L. Cornelius. 1977. Influence of no-tillage and nitrogen fertilization on certain soil properties after five years of continuous corn. Agron. J. 69: 383-386. Brinkman, M. A., D. K. Langer, R. G. Harvey, and A. R. Hardie. 1980. Response of oats to atrazine. Crop Sci. 20:185-189. Buchanan, G. A. and A. E. Hiltbolt. 1973. Performance and persistence of atrazine. weed Sci. 21:413-416. 14. 15. 16. 17. 18. 19. 20. 26 Burnside, O. C., E. L. Schmidt, and R. Behrens. 1961. Dissipation of simazine from the soil. Weeds. 9:477-484. Burnside, O. C., C. R. Fenster, and G. A. Wicks. 1963. Dissipation and leaching of monuron, simazine, and atrazine in Nebraska soils. Weeds. 11:209-213. Burnside, O. C., C. R. Fenster, G. A. Wicks, and J. V. Drew. 1968. Effect of soil and climate on herbicide dissipation. Weed Sci. 17: 241-245. Burnside, O. C., C. R. Fenster, and G. A. Wicks. 1971. Soil persistence of repeated annual application of atrazine. Weed Sci. 19: 290-293 . Burnside, O. C. and G. A. Wicks. 1980. Atrazine carryover in soil in a reduced tillage crop production system. Weed Sci. 28 : 661-666 . Colbert, F. O., V. V. Volk, and A. P. Appleby. 1975. Sorption of atrazine, terbutryn, and G-S—l4254 on natural and lime amended soils. Weed Sci. 23:390-394. Erbach, D. C. and W. G. Lovely. 1975. Effect of plant residue on herbicide performance in no-tillage corn. Weed Sci. 23:512-515. 21. '22. 23. 24. 25. 26. 27. 28. 27 Fenster, C. R., O. C. Burnside and G. A. Wicks. 1957. Chemical fallow studies in winter wheat fallow rotations in western Nebraska. Ag. J. 57:469-470. Foth, H. D. 1978. Fundamentals of soil science. 189-191. Gast, A. 1962. Contributions to the knowledge of the behavior of triazines in soil. Paper presented before the XIV Annual Symposium for Crop Protection,<3ent, Belgium. Gibson, D.‘T. 1968. Microbial degradation of aromatic compounds. Science. 164:389-396. Grover, R. 1966. Influence of organic matter, texture, and available water on the toxicity of simazine in soil. Weed Sci. 14:148-151. Hance, R. J. 1965. The adsorption of urea and some of its derivatives by a variety of soils. weed Research. 5:98-107. Hance, R. J. 1969. Influence of pH, exchangeable cation and the presence of organic matter on the adsorption of some herbicides by montmorillonite. Can. J. Soil Sci. 49:357-364. Hardcastle, W. S. Difference in the tolerance of metribuzin by varieties of soybeans. 1974. weed Research. 14:181-184. 29. 30. 31. 32. 33. 34. 35. 36. 37. 28 Harris, C. I. and G. F. Warren. 1964. Adsorption of herbicides by soil. weeds. 12:120-126. Harris, C. I. 1966. Adsorption, movement, and phytotoxicity of monuron and s-triazine herbicides in soil. weeds. 14:6-10. Harris, C. I. 1967. Fate of 2-chloro-s-triazines in soil. J. Ag. Food Chem. 15:157. Harris, C. I., E. A. Woolson, and B. E. Hummer. 1969. Dissipation of herbicides at three soil depths. weed Sci. 17:27. Harrison, G. W., J. B. Weber, and J. V. Baird. 1975. Herbicide phytotoxicity as affected by selected properties of North carolina soils. weed Sci. 24:120-126. Hartwit, N. L. 1974. Soil and Soil pH effects on the activity of some triazine herbicides. Agric. Lime Dig. 6:34. Herbicide Handbook of the weed Science Society of America. 1983. Hiltbold, A. E. and G. A. Bauchanan. 1977. Influence of soil pH on persistence of atrazine in the field. Weed Sci. 25:515-520. Imbamba, S. K. and D. N. Moss. 1972. Effect of atrazine on physiological processes in leaves. Crop Science. 11:844-848. 38. 39. 40. 41. 42. 43. 44. 29 Jordan, L. 8., B. E. Day, and W. A. Clerx. 1964. Photodecomposition of triazines. Weeds. 12:5-6. Kearney, P. C., T. J. Sheets, and J. w. Smith. 1963. Volatility of seven s-triazines. Weeds. 12:83-87. Kells, J. J., R. L. Blevins, C. E. Rieck, and W. M. Muir. 1980. Effect of pH, nitrogen, and tillage on weed control and corn yield. weed Sci. 28:719-722. Kells, J. J., C. E. Rieck, R. L. Blevins, and W. M. Muir. 1980. Atrazine dissipation as affected by surface pH and tillage. Weed Science. 28:101-104. Kells, J. J. and W. F. Meggitt. 1985. Weed control guide for field crops. Cooperative Extension Service, Michigan State University. E-434. Ladlie, J. S., W. F. Meggitt, and Donald Penner. 1976. Effect of pH on metribuzin activity in the soil. Weed Sci. 24:505-507. Ladlie, J. 8., W. F. Meggitt, and Donald Penner. 1977. Effect of atrazine on soybean tolerance to metribuzin. Weed Sci. 25:115- 121. 45. 46. 47. 48. 49. 50. 51. 30 LeBaron, H. M. 1970. Ways and means to influence the activity and the persistence of triazine herbicides in the soil. Residue Lowder, S. W. and J. B. Weber. 1979. Atrazine retention by crop residue in reduced-tillage systems. Proc. South. Weed Sci. Soc. 32:303-307. Lowder, S. W. and J. B. Weber. 1982. Atrazine efficacy and longevity as affected by tillage, liming, and fertilizer type. McCormick, L. L. and A. E. Hiltbold. 1965. Microbiological decomposition of atrazine and diuron in soil. Weeds. 14:77-82. McGlammery, M. D. and F. W. Slife. 1966. The adsorption and desorption of atrazine as affected by pH, temperature, and concentration. Weeds. 14:237-239. Moschler, W. W., D. C. Martens, C. 1. Rich, and G. M. Shear. 1973. Comparative lime effects on continuous no-tillage and conventional tilled corn. Agron. J. 65:781-783. Nearpass, D. C. 1965. Effects of soil acidity on the adsorption, penetration, and persistence of simazine. weeds. 13:341-346. 52. 53. 54. 55. 56. 57. 58. 59. 31 Papa, B. E. and M. J. Zabik. 1972. J. Agric. Food Chem. 20:316. Parochetti, J. V. 1973. Soil organic matter effect on activity of acetanilides, CDAA and atrazine. Weed Sci. 21:157-160. Putnam, A. R. and J. DeFrank. 1980. Weed control benefits from cover crop residues in no-tillage culture of vegetables. Abs. MESA. p. 35. Oplinger, E. S. 1982. Soybean variety and sencor rate study. University of Wisconsin. Rahman, A. and L. J. Matthews. 1979. Effect of soil organic matter on the phytotoxicity of thirteen s-triazine herbicides. Weed Sci. 27 : 158-161 . Rejto, M., S. Sakzman, A. J. Acher, and L. Muszkat. 1983. Identification of sensitized photooxidation products of s-triazine herbicides in water. J. Agric. Food Chem. 31:138-142. Ritter, W. F., H. P. Johnson, and W. G. Lovely. 1973. Diffusion of atrazine, propachlor, and diazinon in a silt loam soil. Weed Roeth, F. W., T. L. Lavy, and O. C. Burnside. 1969. Atrazine degradation in two soil profiles. weed Sci. 17:202-205. 60. 61. 62. 64. 65. 66. 32 Rogers, E. G. 1967. Leaching of seven s-triazines. Weed Sci. 16: 117-120 . Schnappinger, M. G., C. P. Trapp, J. M. Boyx, and S. W. Pruss. 1977. Soil pH and triazine activity in no-tillage corn as affected by nitrogen and lime applications. Proc. Northeast Weed Sci. Soc. 13: 116. Sheets, T. J. 1961. Uptake and distribution of simazine by oat and cotton seedlings. Weeds. 9:1-13. Sheets, T. J. and W. C. Shaw. 1963. Herbicidal properties and persistence in soil of s-triazines. Weeds. 11:15. Sheets, T. J. 1970. Persistence of triazine herbicides in soil. Residue Review. 32:287-310. Springer-Verlag. Shear, G. M. and W. W. Moschler. 1969. Continuous corn by the no-tillage and conventional tillage methods: a six year comparison. Agr. J. 61:524-527. Sirons, G. J., R. Frank, and T. Sawyer. 1973. Residue of atrazine, cyanazine, and their phytotoxic metabolities in a clay loam soil. J. Agr. Food Chem. 21:1016-1020. 67. 68. 69. 70. 71. 72. 73. 74. 33 Skipper, H. D., C. M. Eilmore, and W. R. Furtick. 1967. Microbial vs. chemical degradation of atrazine in soils. Soil Sci. Soc. Am. Proc. 31:653-656. Skipper, H. D. and V. V. Volk. 1972. Biological and chemical degradation of atrazine in three Oregon soils. weed Sci. 20:344- 347. Smith, D. W. and K. P. Buchholtz. 1962. Transpiration rate reduction in plants with atrazine. Science. 136:263-264. Stevenson, F. J. 1972. Organic matter reactions involving herbicides in soil. J. Environ. Qaulity. 1:333-343. Swain, D.;L 1981. (Atrazine dissipation in irrigated sorghum cropping in southern new South Whales. Weed Research. 21:13-21. Talbert, R. E. and O. H. Fletchall. 1964. Inactivation of simazine and atrazine in the field. weeds. 12:33-37. ‘Talbert, R. E. and O. H..Fletchall. 1965. The adsorption of some s-triazines in soil. weeds. 13:46. Tisdale, S. L. and ML L. Nelson. 1975. Soil fertility and fertilizers. Macmillan Publishing Co., Inc. NY. 75. 76. 77. 78. 79. 80. 81. 34 Triplett, G. B. and G. D. Lytle. 1972. Control and ecology of weeds in continuous corn grown without tillage. Weed Sci. 21:453. Upchurch, R. P. and W. C. Pierce. 1957. The leaching of monuron from lakeland sand soil. I. The effect of amount, intensity, and frequency of simulated rainfall. Weeds. 5:321-330. Upchurch, R. P. and D. D. Mason. 1962. The influence of soil organic matter on the phytotoxicity of herbicides. Weeds. 10:9- 14. Upchurch, R. P., J. A. Keaton, and F. L. Selman. 1968. Soil sterilization properties of monuron, divron, simazine, and isocil. weed Sci. 16:358-364. Walker, A. and D. V. Crawford. 1968. The role of organic matter in adsorption of the triazine herbicides by soil. Pages 91-108 in isotopes and radiation in soil organic matter studies. Proc., Second Symp. International. Atomic Energy Agency, Vienna. Ward, T. M. and J. B. Weber. 1968. Aqueous solubility of alkylamino-s-triazines as a function of pH and molecular structure. J. Agr. Food Chem. 16:959-961. Wax, L. M. and R. Behrens. 1965. Absorption and translocation of atrazine in quackgrass. weeds. 13:107-109. 82. 83. 84. 85. 86. 87. 88. 35 Weber, J. B. and H. D. Coble. 1968. Microbial decomposition of diquat adsorbed on montmorillonite and kaolinite clays. J. Agr. Weber, J. B., S. B. Weed, and T. M. Ward. 1969. Adsorption of s- triazines by soil organic matter. weed Sci. 17:417-421. Weber, J. B. 1970. Mechanisms of adsorption of s-triazines by clay colloids and factors affecting plant availability. Residue Review. 32:93-130. Springer-Verlag. Wicks, G. A. and D. E. Smika. 1973. Chemical fallow in a winter wheat-fallow rotation. Weed Sci. 21:97-102. Wills, G. D., D. E. Davis, and H. H. Funderburk, Jr. 1963. The effect of atrazine on transpiration in corn, cotton, and soybeans. Weeds. 11:253-255. Wilson, H. P. and R. H. Cole. 1964. Effect of formulation, rate and soil moisture on atrazine persistence. Proc. N.E. Weed Control Conf. 18: 358 . Wolfe, N. L., R. G. Zepp, G. L. Baughman, R. C. Fincher, and J. A. Gordon. 1976. Chemical and photochemical transformation of selected pesticides in aquatic systems. U.S.E.P.N. Washington DC, Ecological Research Series PB. 258-846, p 127. CHAPTER 2 FACTORS EFFECTIMS SOYBEAN RESPONSE TO ATRAZINE RESIDUE ABSTRACT Field experiments were initiated in the fall of 1982 to examine the effects of tillage on degradation of atrazine (2-chloro-4- (ethylamino)-6-(isopropylamino)-§_-triazine) in soil. Interactions of atrazine residue with two soybean varieties and six soil applied preemergence herbicide treatments were also examined. Parameters used in evaluation included visual ratings of soybean injury and soybean yield. Injury ratings at growth stage V4 indicated that minimum tillage, such as no-tillage and chisel plowing, resulted in greater atrazine injury than moldboard plowing. Metribuzin (4-amino-6-tert-butyl-3- (methylthio)-g§-triazin-5(4H)-one) at 0.42 kg/ha resulted in the greatest injury of the soybean herbicides tested, regardless of atrazine residue levels. Metribuzin reacted synergistically'with atrazine under chisel plowing. This may have been due to the disturbed trash layer, which allowed the metribuzin to reach the rooting zone and the atrazine residue, which remained in the booting zone under the chisel plowed system. 36 37 'Chloramben (3-amino-2,5-dichlorobenzoic acid) at 3.36 kg/ha resulted in decreased yields under no-tillage. combination of chloramben, lack of rainfall for incorporation, and a light textured soil, may have led to inhibition of root development, which in turn may have resulted in moisture stress and reduced yields. Due to a disturbed trash layer under the chisel and moldboard tillage, moisture stress masked the effect of chloramben. INTRODUCTION It is not uncommon for atrazine (2-chloro-4-(ethylamino)-6- (isopropylamino)-_s_-triazine) applied one year to persist into the next growing season in sufficient concentration to cause injury to sensitive crops planted the following year (1, 3). Tillage influences the degradation and distribution of herbicide residues within the soil profile, which may alter the degree of crop injury the following year (3). Kells (13) found the rate of unextractable 14C- atrazine from soil to be greater under no-tillage compared to conventional tillage. Burnside (7) also found atrazine carryover to be less of a problem under reduced tillage systems compared to conventional tillage. Similar results were found by Bauman and Ross (3). Numerous authors have found pH to be directly linked to the rate of atrazine degradation (4, 5, 12, 13, 15). In an experiment by Best and Weber (4) 35% of the applied atrazine was recovered 5 months after application in a soil of pH 7.5, while only 11% was recovered in 5 months at pH 5.5. Hiltbold and Buchanan (12) found atrazine persistence to be linked to soil texture as well as to pH. An 8 to 9 day increase in persistence occurred in a McLaurin sandy loam per unit pH increase, while a 29 day increase occurred in a Decatur silt loam. 38 39 Most form of ammonium nitrogen fertilizers are acid forming and their continued use lowers the soil pH (24). Lower and Weber (15) found by using NaNO3, a basic nitrogen fertilizer, as the nitrogen source atrazine efficacy and longevity were increased compared to the use of NH4NO3, an acid nitrogen fertilizer. The use of acidifing nitrogen fertilizer in a no-tillage system results in an acid soil surface (13, 16, 22). This results in greater adsorption of atrazine to the soil (10, 16, 18, 20, 25), which in turn leads to more rapid degradation by means of chemical hydrolysis (2, 4, 11, 13, 15). Similarly, if lime were added to the soil surface in a no-tillage situation, an alkaline surface layer would develop, resulting in decreased atrazine degradation (15, 17). Ladlie (16) reported atrazine residue in the soil may interact with metribuzin, resulting in increased injury to soybeans (Glycine max (L.) Merr.). Reduced tillage systems also affect the soil surface in terms of the plant residue remaining. It was once thought that the plant residue would strongly adsorb preemergence herbicides (8). Groover (9), however, showed that picloram (4-amino-3,5,6-trichloropicolinic acid) was not adsorbed on either wheat (Triticum aestivum L.) straw or cellulose. Walker and Crawford (62) also showed that undecayed plant material left on the soil surface did not readily adsorb herbicides. Data from Bauman (3) showed 96 to 90% of the atrazine intercepted by corn (§__e_a_ gays L.) residue was lost 30 days after application and only 1% remained 90 days after application. Elbach (8) found plant residue did not significantly affect weed control when herbicides were applied at the recommended rates, but had an increased influence as rates were reduced. Atrazine retention by crop residue appears to be primarily a function of the total amount of 40 rainfall received and secondly dependent upon residue type and rainfall pattern (15). One 10 cm rain applied immediately or 7 days after atrazine application, removed approximately 87 and 77% of the residue from fresh oat (Avena sativa L.) plants and dry corn trash, respectively. Slightly less was removed when rainfall was applied as four 2.5 cm rains (15). Blevins (6) found no-tillage treatments had higher volumetric moisture contents to a depth of 60 cm during most of the growing season. The greatest difference occurred in the O to 6 cm depth. Soil moisture curves showed different water withdrawal patterns between no- tillage and conventional tillage. The decrease in evaporation and the greater ability to store moisture under no tillage produced a greater water reserve. Residue cover after tillage is dependent on both the crop being tilled under and the type of tillage method employed. The amount of residue left on the soil surface with a chisel plow varies from 10 to 20% with 4 10.2 cm twisted shanks to 50% or greater with narrow points. The percent residue left on the surface is also dependent on the number and type of secondary tillage operations employed in seedbed preperation (8). MATERIALS AND METHODS A field study examining the effects of tillage systems and atrazine residue levels on soybean growth was initiated in the fall of 1982. The site selected was a Kalamazoo loam (Typic Hapludalf, fine- loamy, mixed mesic, 0 to 2% slope, pH 6.8) at the Kellogg Biological 41 Research Station in southwestern Michigan. This site had no recent history of triazine use. In the fall of 1982 three tillage systems were initiated into soybean stubble, these systems being no-tillage, chisel plowing, and moldboard plowing. Four strips of each tillage system were arranged into four blocks in a split plot design. A split plot design was needed due to the impracticality of tilling individual plots. A soil finisher was used to prepare a seedbed on the chisel and moldboard plowed areas in the spring of 1983, prior to planting. Corn ('Pioneer 3747') was planted the second week of May in the same direction tillage was conducted. Atrazine was then applied perpendicularly to the tillage systems at rates of 0, 1.12, or 2.24 kg/ha. Application of all rates were made across all tillage systems in strips within each replication. This was done to reduce complexity in application of the atrazine as well as later herbicide applications. Alachlor at 2.24 kg/ha along with 0.56 kg/ha paraquat plus X-77l was also applied to all plots for grass control and for burndown on the (1/4% v/v) no-tillage plots, respectively. Corn was harvested in the fall and the stalks chopped. Fall tillage was then implemented with each tillage area receiving the same tillage as in 1982. In the spring of 1984, seedbeds on the moldboard and chisel plowed strips were prepared using a soil finisher. Each sub sub-plot (tillage system x atrazine rate) was subdivided into six sub-plots with each 1)(-77 is a nonionic surfactant composed of a mixture of alkylarylpolyoxyethyene glycols, free fatty acids, and isopropenol. 42 receiving a different soybean herbicide treatment. The treatments included were: a) an untreated check, b) chloramben at 3.36 kg/ha, c) metribuzin at 0.42 kg/ha, d) metribuzin at 0.56 kg/ha, e) linuron at 0.84 kg/ha, and f) linuron at 1.12 kg/ha. Treatments were applied May let, 3 days after planting. The entire location was treated with 2.8 kg/ha of alachlor, the no-tillage plots also received 0.56 kg/ha paraquat + X-77 (1/4% v/v). All treatments were applied 207 kilopascals in 215 L/ha of water with a compressed air mounted sprayer on a cub tractor. Two group II soybean varieties were planted in each plot, Northrup King 1492 and Corsoy 79. Corsoy 79 was chosen because of its popularity and its moderate tolerance to metribuzin. NK 1492 was chosen due to its high tolerance to metribuzin. The rational for using two varieties was to check for varietal responces due to tillage, atrazine residue, and soybean herbicides. Visual injury evaluations were taken at the V2, V4, and V7 growth stages. Ratings were made on a 0 to 10 scale, based on reduction in plant vigor and visible signs of herbicide injury, such as leaf chlorosis and necrosis. Yields were determined by harvesting 11.1 meters of the one row plots. Yields were calculated based on 13.0% moisture. RESULTS AND DISCUSS ION No differences in yield occurred between Corsoy 79 and Northrup King 1492, due to tillage systems (Table l). Varietal responses due to atrazine treatment, when averaged over soybean herbicide treatments, existed at soybean growth stages V4 and V7 (Table 2). This occurred 43 Table _l_._ The effect of tillage on varietal differences in soybean yield averaged over atrazine treatments.a Soybean Yield Tillage System Corsoy 79 Northrup King 1492 (kg/ha) No-tillage 1134 A 1176 A Chisel plowed 648 B 546 B Moldboard plowed 786 B 486 B aMeans within columns or rows followed by the same letter are not significantly different at the 10% level according to Duncan's multiple range test. 44 Table 2. Varietal responses, in terms of injury, to atrazine residue under chisel p1 owing.a variety Atrazine Rate Growth Stage Corsoy 79 Northrup King 1492 (kg/ha) (% InjUfY) V2 0 5 C 3 C 1.12 16 B ‘ 14 B 2.24 28 A 24 A V4 0 5 D 1 D 1.12 14 C 16 C 2.24 31 B i 37 A V7 0 4 C 1 D 1.12 7 C 5 CD 2.24 15 B 20 A aMeans within growth stages followed by the same letter are not significantly different at the 5% level according to Duncan's multiple range test. 45 only at the high atrazine levels (2.24 kg/ha) under the chisel plowed system. Corsoy 79 appeared more tolerant to atrazine than Northrup King 1492, but differences were relatively small (Table 2). Soybean herbicide treatments resulted in varietal responses only under moldboard tillage at growth stage at V2 (Table 3). Metribuzin resulted in greater injury to Corsoy 79 than to Northrup King 1492. It has previously been shown that Northrup King 1492 is relatively tolerant to metribuzin when compared to other commonly grown U.S. varieties, including Corsoy 79 (19). It is believed this interaction occurred only under moldboard plowing, due to the zero crop residue cover under this tillage system (Appendix A) and to the dry spring in 1984 (Appendix 8). Under the moldboard system, no crop residue remained on the soil surface to intercept the metribuzin application. No-tillage and chisel plowed plots retained a 45 and 75% residue cover, respectively. Under normal rainfall conditions, crop residue may not have been important, however, without sufficient rainfall the metribuzin may have remained on the crop residue off the soil surface longer on the chisel and no-tillage plots. With chisel plowing, metribuzin application resulted in greater injury to Corsoy 79, however, this was only significant at the 10% level. Chisel plowing left a 45% crop residue cover, which may have allowed more of the metribuzin to reach the soil. No difference in injury occurred under no-tillage, where a 75% residue cover remained (Table 3). Due to the limited varietal interactions and the small differences, which occurred in the existing interactions, only the widely-used Corsoy 79 variety was used in the remainder of the analysis. 45 Table 3; ‘Varietal response to soybean herbicides under three tillage systems averaged over atrazine rates at growth stage V2.3 variety Soybean Tillage Herbicide Rate Corsoy 79 Northrup King 1492 (kg/ha) (% Injury) No-tillage Chloramben 3.36 4 C 6 C Metribuzin 0.42 13 AB 13 A Linuron 0.84 4 C 4 C Untreated - 4 C 8 BC Chisel plowed Chloramben 3.36 9 C 7 C Metribuzin 0.42 24 A 17 AB Linuron 0 84 12 BC 11 BC Untreated - 12 BC 12 BC Moldboard plowed Chloramben 3.36 4 BCD 8 BC Metribuzin 0.42 13 A 6 BCD Linuron 0 84 4 BCD 6 BCD Untreated - 2 D l D aMeans within tillage system followed by the same letter are not significantly different at the 5% level according to Duncan's multiple range test. 47 The greatest series of interactions occurred at growth stage V4. Metribuzin interacted with both rates of atrazine, which resulted in increased injury (Table 4). Ladlie et a1. (14) also found metribuzin to interact with atrazine residue, resulting in increased soybean injury. Synergistic interaction occurred when sublethal atrazine rates increase soybean transpiration and subsequently, increase metr ibuzin uptake. Tillage accomplished two functions, first, atrazine was buried and/or diluted under the moldboard system and was left in place under both no-tillage and chisel plowing. This resulted in equal injury under no-tillage and chisel plowing, both of which were greater than under moldboard plowing (Figure l). Secondly, the crop residue levels under each tillage system were altered. Under the moldboard system, metribuzin reached the soil surface unimpeded, but the atrazine had been diluted, thus there was no interaction between tillage, atrazine and metribusin (Figure 2). However, metribuzin did result in increased injury under moldboard plowing at both atrazine rates, compared to the other soybean herbicide treatments at growth stage V2 (Figure 3). This did not occur under the chisel or no-tillage systems (Figure 4, 5). Metribuzin did not cause increased soybean injury at growth stage V4, probably due to either increased degradation by the time the plants grew to this growth stage or by the soybean root system growing out of the herbicide containing soil zone (Table 4). No-tillage left the atrazine residue intact, but the high crop residue level appears to have inhibited from metribuzin reach the root zone (Figure 2). Sufficient rainfall to incorporate the metribuzin into the root zone did not occur. 48 Table _4_._ The effect of soybean herbicides on injury with increasing atrazine rates at growth stage V4 under three tillage systems.a Atrazine (kg/ha) Tillage Soybean Herbicide Rate 0 1.12 2.24 (kg/ha) -—--—-(% Injury) No-tillage Chloramben 3.36 0 J 0 J 18 C-H Metribuzin 0.42 3 U 5 HIJ 18 C-H Linuron 0.84 O J 5 HIJ 18 C-H Untreated - 0 J 10 F-J 28 BCD Chisel plowed Chloramben 3.36 3 IJ l3 E-J 25 8-8 Metribuzin 0.42 0 J 23 C-F 38 A Linuron 0.84 0 J 10 Pa] 30 ABC Untreated - 0 J 13 E-J 25 8-8 Moldboard plowed Chloramben 3.36 0 J 3 IJ 5 HIJ Metribuzin 0.42 3 IJ 3 U 18 C-H Linuron 0.84 0 J 0 J 20 C-6 Untreated - 0 J 3 IJ 8 G-J aMeans within columns or rows followed by the same letter are not significantly different at the 5% level according to Duncan's multiple range test. 49 Figure 1_._ Soybean injury in 1984 under no-tillage (NT), chisel plowed (CH), and moldboard plowed (MB), following atrazine application in 1983. No herbicide was applied in 1984. 50 SOYBEHN INJURY (V4) 7. so mm mm _a CZHmmmqmu _umu e Z... OI 3m L . 73. PM; 34m3NH2m HZ flmmw arm\ruv 51 Figure 2; Soybean injury in 1984 under no-tillage (NT), chisel plowed (CH), and moldboard plowed (MB), following atrazine application in 1983. Metribuzin was applied preemergence in 1984. 52 SOYBEHN INJURY (V4) 7. on mm mm _a zmdewCNHZ m8. AM xm\:wv J' b IAZINHZN 7:... HZ.~mmw Arm\:ue ~ .~.. 53 Figure _3_._ Soybean injury in 1984, under moldboard plowing, following atrazine application in 1983. Metribuzin (MET), chloramben (CHL), or linuron (LIN) were applied in 1984, or no application was made (UNT). 54 SOYBEHN INJURY (V2) 7. ‘0 mm mm —a zoremomme 7mm Ema DIV FHZ C24 _._m m . IAZDNHZM HZ ummw Arm\3mv 55 mi; Soybean injury in 1984, under chisel plowing, following atrazine application in 1983. Metribuzin (MET), chloramben (CHL), or linuron (LIN) were made in 1984, or no application was made (UNT). 56 SOYBEHN INJURY (V2) 7. ea mm mm _a OIHMH... _Imu mamDNHzm p _.—M Hz _mmo xxmxymc 2m... m .mo 57 Figure_5_:_ Soybean injury in 1984, under no-tillage, following atrazine application in 1983. Metribuzin (MET), chloramben (CHL), or linuron (LIN), were applied in 1984, or no application was made (UNT). 58 SOYBEHN INJURY (V2) 7. as ma ND _8 zouqurmmm _Imu 3m... 52 \1 01.: _._m m.~¢ IAEDNHZN HZ ummw Arm\:wv 59 Chisel plowing loosened the soil as opposed to turning it over as in moldboard plowing, therefore, the atrazine residue remained relatively undisturbed. Chisel plowing does, however, incorporate some of the surface plant residue into the soil. When metribuzin was applied under this tillage system, more of it may have reached the soil due to the reduction in plant residue cover. This resulted in a three- way interaction between atrazine, metribuzin and the chisel plowing system at growth stage V4 (Figure 2). Under chisel plowing sublethal levels of atrazine may have increased transpiration which in turn may have increased metribuzin uptake and therefore resulted in increased injury. Chloramben and linuron were not involved in three-way interactions with tillage, varieties or atrazine residue levels (Figures 6 and 7). No interactions between tillage, soybean herbicides and atrazine residue levels occurred at growth stage V7 (Figures 8, 9 and 10). Atriazine and/or metribuzin may have degraded to levels low enough not to show interactions with tillage or each other. Another explanation may be that at this stage the root system may have grown past the herbicide containing soil zone. During a dry year, such as 1984, the root system may have grown deeper in seach for water. A combination of these explanations is probably the case. Atrazine application independently influenced injury at all growing stages, (Table 2), along with interacting with both soybean herbicides and tillage at V4 (Table 4). As expected, soybean injury increased as atrazine rate increased. Although tillage did not significantly influence yield at the 5% level according to Duncan's Multiple Range Test, it did at the 10% 60 Figure _6_._ Soybean injury in 1984, under no-tillage (NT), chisel plowed (CH), and moldboard plowed (MB), following atrazine application in 1983. Chloramben was applied preemergence in 1984. 61 SOYBEHN INJURY (V4) 7. ‘5 mm mm _a nIrommzwmz mm.wm rm\:mv qu e. EHmDNHZm _Lm Hz _mmw Armxroc .NA 62 Figure_7_._ Soybean injury in 1984, under no-tillage (NT), chisel plowed (CH), and moldboard plowed (MB), following atrazine application in 1983. Linuron was applied preemergence in 1984. 63 SOYBEHN INJURY (V4) 2 AS mm mm _a FHZCEOZ as. me rmWIm—V A .19”. OI 2... 3m _Lm EHNINHZN HZ _wmw Arm\:wv m .m. 64 Figure _8_=_ Soybean injury in 1984, under moldboard plowing, following atrazine application in 1983. Metribuzin (MET), chloramben (CHL), or linuron (LIN), were applied in 1984, or no application was made (UNT). 65 SOYBEHN INJURY (V7) 7. 1.8 ma ms us :oremomme r _umu OIF . 3m._. :2 11 C2... _Lm mammNHzm Hz _mmw xxmxyuc .MA 66 Figure_9_:_ Soybean injury in 1984, under no-tillage, following atrazine application in 1983. Metribuzin (MET), chloramben (CHL), or linuron (LIN), were applied in 1984, or no application was made (UNT). 67 SOYBEFIN INJURY (V?) 7. +5 ma ND #0 zouqHTrmom qu OI... 3m... _IHZ CZ... p L ~._m PM; mammNHzm Hz _mmm Irmxyue 68 Figure 10. Soybean injury in 1984, under chisel plowing, following atrazine application in 1983. Metribuzin (MET), chloramben (CHL), or linuron (LIN), were applied in 1984, or no application was made (UNT). 69 SOYBEHN INJURY (V?) X As mm mm ~m _umu OIHMNF _. p —m 3m._. 52 DIV 34mINH2m HZ _mmw arm\rwv CZ._. . m .ma 70 level. No-tillage resulted in the greatest soybean seed yields (Table 5L. This was probably due to increased moisture conservation under the no-tillage system in response to the high crop residue level. Tillage interacted with chloramben, resulting in a decrease in yield under the no-tillage system (Figure 11). Chloramben was applied at 3.36 kg/ha on a Kalamazoo loam soil, characterized by mid-summer droughtiness. The effect of this somewhat high rate was compounded by the lack of rainfall, which resulted in the chloramben remaining near the root zone for an extended period of time. This may have inhibited seedling root development, as stated by Ross (20), which would have resulted in increased moisture stress compared to the other soybean herbicide treatments under the no-tillage system. In the chisel and moldboard tillage systems, the crop residue layer was reduced or non-existent. Therefore, moisture conservation was poor and moisture stress had already occurred in all of the soybean herbicide treatments, which masked any affect of chloramben. In conclusion, atrazine-metribuzin interactions occurred when both were available for plant uptake» Chisel plowing resulted in the greatest combination of atrazine and metribuzin uptake as shown in terms of injury, at growth stage V4. This interaction was masked in terms of soybean yield due to moisture stress. Chloramben inhibited root development, which led to decreased yields due to moisture stress under no-tillage. Drought stress masked this under chisel and moldboard-tillage systems. 71 Table 5. The effect of tillage system on soybean yield.a Tillage System Yield (kg/ha) No-tillage 1134 A Chisel plowed 648 B Moldboard plowed 786 B aMeans followed by the same letter are not significantly different at the 10% level according to Duncan's multiple range test. 72 Figure 11. The effect of soybean herbicides on yield within three tillage systems, no tillage *NT), chisel plowing (CH), and moldboard plowing (MB). All treatments were maintained in a weed free environment. 73 KG/HFI 3.50 was :24 01? Ina ruz Z... mo