herbicide sorption 2

The reason glyphosate is not applied as a preemergence herbicide is because

• it is quickly broken down by microbes and has no residual activity

• it is so tightly sorbed to soil it is unavailable for plant uptake

• it is only taken up by leaves, not roots, so it must be applied to the leaf tissu

Herbicides with negative charges, like dicamba,

• are sorbed tightly to the soil and are unavailable to the plant

• have very little sorption to soil or organic matter and are often found in groundwater aquifers

• are not sorbed to soil but rarely leach to aquifers because of rapid microbial degradation

If a herbicide solution is spiked with a small amount of radioactive chemical

• it is easy to detect after extraction but may not be the parent compound

• is easy to detect and remains as the parent compound so no additional analysis is needed

• is always a safety hazard and should never be used

The partition coefficient (Kd) and the Freundlich isotherm

• provide the same answers about sorption

• are basically the same but the partition coefficient is preferred

• the Freundlich isotherm provides greater information about sorption at high and low initial concentrations

Desorption isotherms are

• usually do not fall on top of the sorption isotherm, indicating that some chemical is more tightly bound to the soil

• usually do not fall on top of the sorption isotherm indicating that desorption is a less energetic process than sorption

• usually have near equal values, i.e. sorption = desorption