Herbicides banding

Sorption mechanism of atrazine by SOM has been a subject of controversy. The early works (Weber et al., 1969 Hayes, 1970) showed that the sorption process is inhibited due to the low pKa value of herbicide, along with the proton transfer between carboxylic groups as well as the charger transfer at low pH values. These were discussed as probable retention mechanisms by organic colloids. However, Martin-Neto et al. (1994b, 2001) observed by FTIR (Figure 16.16) and UV-vis spectra that a charge-transfer mechanism was not operative in the HA-atrazine (HA-AT) interaction. FTIR showed that in pH <4, the carboxylate band (1610 cm-1) was observed in HA-AT spectrum, but a decrease in the wavenumber of C-H... 

During the late 1950s and early 1960s, most soil-applied herbicides typically did not receive mechanical incorporation, and when rain was insufficient, lacked reliability in controlling weeds. The reason for the slow adoption of mechanical incorporation techniques was probably three-fold (a) banded applications were preferred from a cost standpoint (b) the advantages of soil incorporation were not universally recognized and (c) the equipment and techniques for adequate incorporation were not available. Poor soil incorporation not only resulted in poor weed control, but in some cases resulted in crop injury. Simazine, in spite of its good weed control spectrum in corn, was never widely used in the Central Plains. Its lack of acceptance was attributed to its soil residual with the potential to injure... 

Figure 4.7 A band of herbicide over the row saved farmers the expense of treating the entire soil area in a field. (Courtesy of Dr. Ellery Knake, Professor Emeritus, University of Illinois.)...

On the other hand, the broad weed control spectrum of chloramben, which was introduced in 1959, brought with it widespread acceptance. As an over-the-row band for control of both broadleaf and grass weeds, cost was minimized. With good crop tolerance, chloramben dominated the early soybean herbicide market. During 1972, 85% of the product was applied as the granular formulation (Table 4.2). However, as application practices changed for the soybean crop, banded applications became an inconvenience. Herbicides such as metribuzin (a triazine herbicide), linuron, and bentazon, which could be applied as an affordable broadcast treatment, soon became products of choice, and the marketing of chloramben was eventually discontinued in 1990. 

The ability of one product to complement the characteristics of another has also had an effect on product acceptance. Although alachlor initially was used by itself as a banded granular grass herbicide on com and soybean, it was the tank mixes with broadleaf herbicides that propelled its success. Combinations of atrazine-alachlor, metribuzin-alachlor, and linuron-alachlor became very common. Alachlor replaced essentially all propachlor use on field corn over the 4-year period from 1972 to 1976, not only as a result of less hazardous handling characteristics (Table 4.1), but also as a consequence of its success in tank mixes. 

The sugarcane industry in the United States and worldwide is highly dependent on the continued availability of triazine herbicides. In the United States, growers use reduced quantities of atrazine by applying it as a band over the row. Ametryn is strategically important as a postemergence treatment. The loss of any of the most essential sugarcane... 

Farmers use cultivation and herbicides in their weed control programs because of their complementary nature in controlling weed species that are missed if exclusive reliance were to be placed on either technique alone. One way to decrease herbicide use with additional cultivation while controlling weeds in the corn row is to band the herbicide over the row of corn plants. Essentially, the herbicide controls the weeds within the row, while the weeds between the rows are effectively controlled with mechanical cultivation. 

Banding of herbicides is not a new practice. In fact, when herbicides were first introduced for com production, it was common to band herbicides in order to keep herbicide costs low. However, farmers have largely replaced banding of herbicides in corn with broadcast sprays over the entire field. In 1993 in the US Com Belt, 16% of the com acreage was banded (USDA ERS, 1994). The rate of banding was highest in Nebraska (50%) and lowest in Illinois (3%). 

Tn 1968 T. G. Sherbeck and E. S. Oplinger (two of my graduate stu-dents) screened 17 PGR chemicals on com. Many of these chemicals were herbicides and were added to the starter fertihzer band applied on com. Why in the fertilizer band Earlier work with TIB A (3,5-triiodo-benzoic acid) in the fertilizer band on soybeans had shown promise for increasing grain yields (J). 

This operation can induce extrinsic variability in agrochemical concentrations and fluxes in soils due to variability in application itself (random if broadcast nonrandom if banded) and the tillage operation. Weed scientists have examined such variability, in particular as related to herbicide efficacy ( 15 - 21 ). Such extrinsic variability in pesticide concentrations can also pose serious problems in obtaining representative soil samples for pesticide concentration determinations. 

Zinc oxide (band gap equivalent to 370-nm light) is capable of photooxidizing alkanes to alkanones (Giannotti et al., 1983) and of photodegrading the herbicides molinate (12) and thiobencarb (13) in agricultural wastewaters (Draper and Crosby, 1987 Figure 6.10). The use of ZnO in the latter instance is especially promising since the oxide is used in fertilizers as a source of zinc for crop nutrition. ZnO produced... 

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