Exam 3- Herbicides and Soil
Pre-plant Treatments
applied to soil prior to planting
Pre-emergent treatments
applied to the soil during ot after planting, but before either the crop/ weeds have emerged
Transfer Processes: plants can serve as ____ to remove harmful chemicals and elements from the soil
bioremediators
Degradation
breakdown of herbicide
Degradation: Biodegradation: Microbial decomposition
breakdown of herbicides by algae, fungi, actinomycetes and bacteria
Degradation: Chemical degradation
breakdown of herbicides by chemical reactions not directly involving living organisms
Sorption: ___ and ___ soils usually require higher herbicide rates
clay and organic soils
Presence of crop residue: favors better soil aggregation
creating wider channels for water infiltration into soil
Degradation: Biodegradation: Higher Plants
degrade herbicides after they absorb them
Degradation: Biodegradation
detoxification/ breakdown by living organisms
Soil type may ____ of some herbicides
dictate recommended rates
Transfer Processes: Exudation
discharge of chemical into the soil environment by microorganisms and higher plants that have absorbed herbicide
Tillage can promote
erosion
Transfer Processes: Volatilization
evaporation into the gaseous state
Degradation: Photodegradation
herbicide breakdown by light
Transfer Processes: Removal by Higher Plants
herbicides are stored by plants then stores and metabolized
Herbicides must be ___ in sufficient quantities to take up and achieve kill
in the soil zone where germinating weed seeds will contact the chemical
Annual dropseed, prairie three awn
indicated dry, often low fertility soils
Half life of a herbicide is the
length of time it takes for one-half of the original amount of herbicide to break down
Presence of crop residue: increases soil acidity
may affect herbicide ionization and polarity
Broomsedge
may indicate acidic, low fertility, overgrazed soils
Goosegrass, stinkgrass, tufted lovegrass, common hardgrass
may indicate compacted, sometimes wet soils
Extended Persistence
may result in carryover or residues high enough to effect next seasons cultural/planting activities
May need to use ____ ____ to avoid photodecomposition or volatilization of some chemicals
mechanical incorporation
Incorporated planting
mechanically mixed into soil
Need ___ to allow movement into soil solution for plants, but too much water may leach herbicide out of germination zone
moisture
Transfer Processes: Volatilization can also allow the herbicide to ___ of soil into atmosphere
move out
Activated planting
moved into top inches of soil by water
Sorption: Leaching
movement of herbicide with water -normally downward -inversely related to % clay and SOM -soil pH influences sorption if the herbicide carries a charge
Soil can keep limited mobility herbicides ___ so deep rooted crops not affected
near the surface
Red sorrel
often indicates acidic soild
Prostrate knotweed, spotted spurge
often occur in compacted, dry soils
Transfer Processes: Exudation can be either in __ form or ____ form of herbicide
original or metabolized
Soil can be a site of
pesticide movement
Sorption: Soil colloid adsorption
polarity of herbicide and organic fraction will affect a herbicides soil adsorption
Presence of crop residue: Increases soil organic matter near soil surface
potentially adsorbing herbicides before reaching soil
Soil can control herbicide availability due to
soil adsorption of the herbicide
Cultivation and chemical apllication equipment can cause
soil compaction
Presence of crop residue: Increases ___ population
soil microbial
Can use a ____ herbicide to kill deep-rooted plants and not injure top soil plants
soil mobile
Presence of crop residue: increases ___ levels
soil moisture
Need to have some ____ of the active form of a soil-applies herbicide so as to achieve desired weed control
soil persistence
For ___, herbicides must remain in high enough concentrations for long periods to kill germinating weeds and existing plant roots
soil sterilization
Degradation: Microbial organisms use herbicies as
source of organic food
Degradation: Biodegradation: ___ will kill microorganisms, delaying breakdown of chemicals
sterilizing soil
Soil may be ____ or ____ of herbicide application
target/ off target recipient
Soil can bind or ___ herbicides so only above-ground portions contacted by chemical are affected
tie up
Lambsquarters, pigweeds
usually indicates fertile, well-drained soils
Yellow nutsedge, smartweed
usually observed in moist soild, but will grow anywhere
Transfer Processes: Volatilization depends on ___ of the herbicide
vapor pressure -higher vapor pressure=more volatile
Degradation: Degradation is usually fastest in
warm temps with adequate soil moisture
Transfer Processes: Volatilization can allow a herbicide to move ___ soil
within
Degradation: Degradation processes include
-Biodegradation -Chemical degradation -Photodegradation
Degradation: Length of time to degrade depends on
-dosage -environment -binding -microorganisms
Pesticide Movement
-herbicide runoff through surface water -herbicide adsorbed to soil particles washed away by surface water -herbicides can percolate/ leach into groundwater
Degradation: Photodegradation accounts for breakdown of chemicals that are ____ or ____ into soil
-not watered -mechanically incorporated
Degradation: Chemical degradation examples
-oxidation/ reduction -precipitation -dissociation -ionic bonding to soil ions/ chemicals
Herbicides can be applied directly to the soil as:
-pre-plant treatments -pre-emergent treatments
Degradation: Biodegradation is done by
-soil microorganisms -higher plants
Degradation: Affects the speed of microbial degradation
-soil pH -oxygen content -minerl content -moisture levels
Factors that affect soil persistence of a herbicide can be
-sorption -degradation -transfer process
Transfer Processes
-volatility of the herbicide -absorption by higher plants -exudation by higher plants
Degradation: Biodegradation: Microbial decomposition works best in
72-90 degrees F -moist, aerated soil conditions
Soil contains
a living community (constantly changing)
