**3. Conclusion**

Biochars, the by-products of pyrolitic conversion processes of vegetative biomass to gas, biooil, or other fuels, are proposed soil amendments for many diverse purposes. Biomass feedstocks and production processes vary depending on the desired end-products. This study measured the influence of several microwave pyrolitic conversion processes, which varied temperature and residence time, on pH and EC characteristics of the resulting biochars produced from maize stover and switchgrass. These biochars were used to amend a silty clay loam soil and examined the solution pH, EC, and sorption properties of a weakly cationic herbicide, atrazine, and an anionic herbicide, 2,4-D.

The microwave pyrolysis parameters of processing time and temperature of maize stover and switchgrass produced biochars that had a range of characteristics, with enough variation that they should not be thought of as a single entity with uniform properties. Short processing times (<10 min) of either feedstock at high (650ºC) or low (550ºC) temperature resulted in biochar with a pH < 4.5. Biochars produced with processing times >15 min at high temperature resulted in materials with pHs >8. Processing at intermediate temperatures and times resulted in char pHs ranging from 5.6 to 6.5. Adding 1% char to soil did not impact soil pH (6.4) whereas adding 10% biochar decreased soil pH a maximum of 12% when low pH biochars were used or increased soil pH up to 7% when high pH biochars were applied. "Native" soil EC was 1.63 mS/cm. Soils amended with 1% or 10% biochar ranged from -20% lower up to 39% higher EC values depending on biochar type and amount added. The biochars used in this study would be considered 'fresh', and not aged or post-process treated. Aging biochar or treating with steam or oxygen has been reported to dramatically change pH and other properties. Studies on these materials would need to be conducted to determine if results are similar to those reported for this study.

In a 2010 literature review, Kookana (2010) stated that there were limited published studies on the effect of biochars on pesticide efficacy and fate in soil, although in the few studies where sorption is reported, the sorption coefficients could be as high as >2000 times those of soil. Results from our study confirmed that when biochars were used as a single sorption material very high sorption amounts could be observed for both a cationic and an anionic compound. Herbicide sorption Kd to all biochars alone was very high compared with soil but varied among biochar types. Soil amended with 1% maize stover biochar had herbicide sorption values similar to unamended soil. However, adding 10% biochar amendment increased both atrazine and 2,4-D sorption coefficients by many-fold. A neutral herbicide, alachlor, has also been shown to have increased sorption in soils amended with woodchip biochar addition (Spokas et al., 2009). If biochars are applied to production fields, biochars may reduce atrazine preemergence weed control due to decreased availability to emerging seedlings. Kookana (2010) also discussed the possibility of longer residence time of pesticides due to reduced bioavailability, which may influence further the impact of a pesticide on ecotoxicology and potential accumulation. Indeed, Jones et al. (2011) reported biochar addition suppressed simazine biodegradation due to limiting availability to soil microbes through increased sorption, although leaching potential was reduced simultaneously.

The results of this study along with other reports have implications on best use of biochar in agricultural fields. If biochar has no or little effect on pesticide sorption, efficacy, or EC values, then the material may be suitable for general application in agricultural fields and highly desirable if it can be used to increase water holding capacity or as a nutrient source. Biochars, if high in sorption capacity, may be applied strategically and could accomplish important roles in ecosystem health and environmental quality. Biochar, added in filter strips and waterways, eroded landscapes, or other areas where increased sorption is desired, may aid in cleaning water running off fields by sorbing undesirable contaminants. Increased sorption may also slow or stop herbicides from leaching, so highly sorbent biochar types may be desired over shallow aquifers or in areas low in native organic matter (Wang et al., 2010). Herbicide bioavailability in some cases may be reduced, protecting sensitive plants.

Conversely, the effect of spreading biochars across entire fields may have negative results and be undesirable. One consequence may be that the materials increase soil EC values to saline levels. In addition, if the biochar reduces the efficacy of soil-applied herbicides or other pesticides this may have negative impacts. Reduced pesticide efficacy would require higher herbicide application rates to be as effective as lower rates. This would have monetary implications for growers and field managers by increasing management costs. Increased sorption, in some cases, also may increase the recalcitrance of pesticides leading to longer residence times in the environment. The occurrence of greater recalcitrance may be desirable if bioactivity was still acceptable and longer activity of the pesticide was desired to control the pest of interest. However, longer residence time may lead to other long-term environmental problems, such as greater leaching potential or carry-over problems into the following season.

Prior to any regular field applications of any biochar, the biochar properties must be examined to determine the suitability of the material for the long-term management of a particular site. The reasons for the application should be defined clearly and the outcomes closely monitored to determine if expectations and results are synonymous.

#### **4. Acknowledgments**

Funding provided by South Dakota Maize Utilization Council, US USDA/Sun Grant Initiative, and South Dakota Agricultural Experiment Station. Undergraduate participation included Mr. Mitch Olson, Mr. Dan Clay, and Ms. Kaitlynn Krack.

#### **5. References**

70 Herbicides – Properties, Synthesis and Control of Weeds

Biochars, the by-products of pyrolitic conversion processes of vegetative biomass to gas, biooil, or other fuels, are proposed soil amendments for many diverse purposes. Biomass feedstocks and production processes vary depending on the desired end-products. This study measured the influence of several microwave pyrolitic conversion processes, which varied temperature and residence time, on pH and EC characteristics of the resulting biochars produced from maize stover and switchgrass. These biochars were used to amend a silty clay loam soil and examined the solution pH, EC, and sorption properties of a weakly

The microwave pyrolysis parameters of processing time and temperature of maize stover and switchgrass produced biochars that had a range of characteristics, with enough variation that they should not be thought of as a single entity with uniform properties. Short processing times (<10 min) of either feedstock at high (650ºC) or low (550ºC) temperature resulted in biochar with a pH < 4.5. Biochars produced with processing times >15 min at high temperature resulted in materials with pHs >8. Processing at intermediate temperatures and times resulted in char pHs ranging from 5.6 to 6.5. Adding 1% char to soil did not impact soil pH (6.4) whereas adding 10% biochar decreased soil pH a maximum of 12% when low pH biochars were used or increased soil pH up to 7% when high pH biochars were applied. "Native" soil EC was 1.63 mS/cm. Soils amended with 1% or 10% biochar ranged from -20% lower up to 39% higher EC values depending on biochar type and amount added. The biochars used in this study would be considered 'fresh', and not aged or post-process treated. Aging biochar or treating with steam or oxygen has been reported to dramatically change pH and other properties. Studies on these materials would need to be

In a 2010 literature review, Kookana (2010) stated that there were limited published studies on the effect of biochars on pesticide efficacy and fate in soil, although in the few studies where sorption is reported, the sorption coefficients could be as high as >2000 times those of soil. Results from our study confirmed that when biochars were used as a single sorption material very high sorption amounts could be observed for both a cationic and an anionic compound. Herbicide sorption Kd to all biochars alone was very high compared with soil but varied among biochar types. Soil amended with 1% maize stover biochar had herbicide sorption values similar to unamended soil. However, adding 10% biochar amendment increased both atrazine and 2,4-D sorption coefficients by many-fold. A neutral herbicide, alachlor, has also been shown to have increased sorption in soils amended with woodchip biochar addition (Spokas et al., 2009). If biochars are applied to production fields, biochars may reduce atrazine preemergence weed control due to decreased availability to emerging seedlings. Kookana (2010) also discussed the possibility of longer residence time of pesticides due to reduced bioavailability, which may influence further the impact of a pesticide on ecotoxicology and potential accumulation. Indeed, Jones et al. (2011) reported biochar addition suppressed simazine biodegradation due to limiting availability to soil microbes through increased sorption, although leaching potential was reduced

The results of this study along with other reports have implications on best use of biochar in agricultural fields. If biochar has no or little effect on pesticide sorption, efficacy, or EC values, then the material may be suitable for general application in agricultural fields and

conducted to determine if results are similar to those reported for this study.

cationic herbicide, atrazine, and an anionic herbicide, 2,4-D.

**3. Conclusion** 

simultaneously.


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producing bioenergy, permanently sequestering carbon, while improving soil and


**5** 

*Spain* 

R1

O

N OR2

OH

R4

R3

R3´

**Chemical Behaviour and Herbicidal Activity** 

*Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA)* 

Benzoximate (I; Fig. 1) is an acaricide developed by Nippon Soda in 1971 (Iwataki, 1992). However, scientifics of the company observed that some benzohydroxamates showed weak herbicidal activity. After much synthetic developments, a new lead compound, an ethoxyimino dehydroacetic acid derivative (II; Fig. 1), showed a strong pre-emergence herbicidal activity against annual grass weed without any effects towards broadleaf plants. Further developmental research was performed on the cyclohexanedione skeleton to develop a new post-emergence herbicide. It was observed that the ethoximine group between the two keto groups was essential for the herbicidal activity (III; Fig. 1). Besides, when hetero atoms were introduced in the ring, the compounds showed high preemergence activity. When the ring was formed by carbons, so-called cyclohexane derivatives, the compounds showed high pre- and post-emergence activities. Therefore, the synthetic research was focused towards the substituents on the cyclohexanodione skeleton. The activity was higher when side chain substituents R1 and R2 (Fig. 1) were alkyl groups. As for the ring substituents, mono i-Pr and germinal dimethyl at the R3 and R3´ position and ciano and methoxycarbonyl groups at the R4 position provided the maximum activity. This

way, alloxydim–sodium was discovered and introduced in the market in 1978.

H3C

O

However, though alloxydim-sodium showed a potent activity against annual grass weeds, it did not against perennial grass weeds. Therefore, the synthetic research was focused towards the introduction of different substituents on the cyclohexane ring, since the structure-activity pattern of the skeletal had been already identified. It was disclosed that

I Benzoximate II III

Fig. 1. Pathway of lead compounds towards the discovery of cyclohexanedione oxime

OH

CH3

O CH2CH3

O

N

O

O CH2CH3

O

C

OCH3

OCH3

Cl

herbicides.

N

**1. Introduction** 

**of Cyclohexanedione Oxime Herbicides** 

Pilar Sandín-España, Beatriz Sevilla-Morán,

José Luis Alonso-Prados and Inés Santín-Montanyá

