Who was known as the "Father of Soil Conservation" in the US?
Hugh Hammond Bennett
How many square feet are there in an acre?
43,560
How do you calculate the amount of nitrogen from a square foot of (biomass) dry weight?
Using Dr. Peet's method:
dry weight x 43,560 = lbs per acre
lbs per acre x amount given (.0362 for Austrian winter pea) - amount given (9.2 for winter pea)
The interaction of Rhizobium bacteria with legume crops such as bean or soybean is an example of what kind of mutualism?
inhabitational
A cover crop that is allowed to grow within the crop is called
Living mulch
According to the Hoyt (2005) data, corn yields were higher at most levels of fertilization following
A hairy vetch cover crop
Alleopathy
Is an effect of one species on another through chemicals
Can be used to suppress the germination and growth of weeds
Effectivenes has been observed to change with the plant's stage of growth
A way to increase genetic and species diversity within a cropped field:
Intercropping
Strip cropping
Cover cropping
T/F In terms of agro-ecosystem diversity, an example of undesirable "simplification" of the system would be the loss of predatory insects through indiscriminate use of a broad-spectrum insecticide
True
T/F Living mulches can keep soil coooler, reduce weeeds and erosion, but they might also compete with the crop for soil moisture
True
T/F In the USA, water erosion is typically a bigger problem in western states
False (eastern states because they have more rainfall)
T/F Beneficial use of cover crops is restricted to providing cover during late fall, winter and early spring seasons
False
T/F Island biogeography theory has been applied to pest and beneficial insects in agricultural fields to better understand how they are distributed into a crop such as soybean or a vineyard
True
Human-accelerated erosion can increase geological erosion by how much?
10 to 1000 times
Land equivalent ratio
provides an all-other-things-equal measurement of the yield advantage obtained by growing two or more crops as an intercrop compared to growing the same crops as a collection of separate monocultures
ephemeral gulleys
occur in same place every year
what type of slope is good for farm land?
0-2 good
2-5 okay
6 - you're on the edge of good farm land
How likely is Greene County to get 3 inches of rainfall in a 24 hour period?
About once every two years (based on probablility)
T/F In one large rainfall event, you could see 70-80 percent of rain-caused erosion for an entire year
True
Soil erosion
removal of thin layers over time
think of the pages in a book being removed one by one
gully erosion
too big to be smoothed over or crossed with equipment
rill erosion
usually follows crop rows
where does wind erosion occur?
drier landscapes
vegetative cover is critical to prevent wind or water erosion?
both
Why was Hugh Hammond Bennett considered a visionary?
He realized the value of land cover, realized we could not continue farming the way we were and he organized research
How much cover is needed to begin to get into conservation tillage levels?
At least 30%
Conventional tillage is usually around 3-5% cover
No till - about 90% cover
Low-residue - about 25-30% cover
Buffer - 90-100% cover
Wind breaks offer crops shelter from wind erosion/damage. If you have a 10 foot tall tree, how many feet of cover will you provide?
100 feet (10 times)
In "The Cattle Vote", how did the cattle vote?
1 month in: equal
2 months in: 3/4 cattle preferred treated side
3 months in: 84% treated
4 months in: 73%
overall: 74% treated
In "The Cattle Vote", what would the weed component of the yield be on the untreated side?
50%
What problem can arise with grazing fescue only?
fescue toxicosis (or endophyte toxicosis)
summer slump - reduced food intake, head down, mouth open, coronary band (swelling, redness, necrosis)
onset usually 1-6 weeks after grazing stockpiled fescue begins
what months would it be best to avoid grazing fescue pasture?
November - when flowering is at its peak
end of May, early September (when concentrations are higher near the base of plants)
If you're looking for weed control but don't want to use a herbicide, what else might you consider?
Mixing in some goats
20% reduction in woody vegetation in 8 weeks, 94% after four growing seasons
Vernalization
Planting in different seasons - using winter-planted crops in spring as a cover crop, for example
In crop communities, what are characteristics which exist only at the community level called?
Emergent qualities
How does conventional agriculture differ from an agroecological approach when it comes to the crop community?
Conventional - simplifies (reduce to a single crop population growing in an otherwise sterile abiotic environment)
Agroecological - understand species interactions in the conext of the larger community (beneficial species interactions, some complexity desirable)
organism-organism interactions can be conceptualized as interferences. what does this mean?
an organism has some kind of impact on its environment, and through this impact, another organism is affected
removal interferences
the removal of some resource by one or both of the interacting organisms
addition interferences
one or both organisms add some substance or structure to the environment
Interferences can have beneficial, detrimental or neutral effects on neighboring organisms. Does it matter the interference is a removal interference or an addition interference?
No. Either can have those types of effects
What does competitive exclusion suggest?
That two species with similar needs cannot occupy the same niche or place in the environment
This doesn't fully apply in many communities
What is an important way that agroecosystems allow for the coexistence of species in a multiple cropping community?
by combining species with slightly different physiological characteristics
T/F Species with a mutualistic relationship are not only able to coexist, but are dependent on each other for optimal development
True
Inhabitational mutualisms
One mutualist lives wholly or partly inside the other
ex: Rhizobium bacteria and leguminous plants
Exhabitational mutualisms
The organisms involved are relatively independent physically, but interact directly
Ex: the relationship between a flowering plant and its pollinating insect
Indirect mutualisms
The interactions among a set of species modify the environment in which they all live to the benefit of the mixture.
Involve more than two species and can include both inhabitational and exhabitational mutualsims
How do mutualisms in agroecosystems increase the resistance of the entire system to the negative impacts of pests, diseases and weeds?
By contributing beneficial interactions
Cover crops
plant species (usually grasses or legumes) grown in pure or mixed stands to cover the soil of the crop community for part or all of the year.
When cover crops are tilled into the soil, the organic matter added to the soil is called
green manure
When cover crops are grown directly in association with other crops they are called
living mulch
Benefits to the crop community from cover crops:
reduced soil erosion
improved soil structure
enhanced soil fertility
supression of weeds, insects and pathogens
What are some problems that can occur from poorly planned cover crop systems?
If resources are limiting, the could be competitive interference
If allowed to become too dense, some cover crop may be alleopathic to the crop
Damaging herbivores or disease organisms may find the cover crop species to be an ideal alternate hoste, later moving onto the crop
Crop residue may interfere with cultivation, weeding, harvesting or other farming activities
How can weeds be beneficial?
They can protect the soil surface from erosion through root and foliar cover
Take up nutrients that might otherwise be leached from the system
Add organic matter to the soil
Selectively inhibit the development of more noxious species through allelopathy
What conditions are weeds especially well-adapted to?
Simplified, disturbed habitats
Intercropping
When two or more crops are planted together in the same cropping system
corn-bean-squash polyculture
In a series of studies of the corn-bean-squash polyculture done in Tabasco, Mexico, it was shown that corn yields could be stimulated as much as 50% beyond monoculture yields when planted with beans and squash. What happened to the yield of the other two crops?
There was significant yield reduction for the other two species, but the total yields for the three crops together were higher than what would have been obtained in an equivalent area planted to monocultures of the three crops
Ecological diversity
a broadened and complexified concept of diversity, it includes dimmensions such as:
species
genetic
vertical
horizontal
structural
functional
temporal
Once diversity is generated, it tends to be self-reinforcing. Explain?
Greater species diversity leads to greater differentiation of habitats and greater productivity, which in turn allow even greater diversity
alpha diversity
species diversity in a single location
beta diversity
species diversity across communities or habitats
gamma diversity
a measurement of the species diversity of a region such as a mountain range or river valley
T/F Studies of natural ecosystems in early stages of development or following disturbance have shown that all of the dimensions of diversity tend to decrease over time.
False. They increase
Secondary succession
the ecosystem's recovery process after a disturbance
the system begins to restore the diversity of species, interactions and processes that existed before disturbance
(ecosystem) maturity
the successional condition in which the full potential for energy flow, nutrient cycling and population dynamics in that physical environment can be realized
the structural and functional diversity of the ecosystem at maturity provides resistance to change in the face of further minor disturbance
In what stage does an ecosystem reach its highest level of species diversity?
As a system approaches maturity
biomass continues to increase at maturity, though at a slower rate
Why are agroecosytems considered ecologically unstable?
Loss of diversity weakens the functional links between species that characterize natural ecosystems
Nutrient cycling rates and efficiency change
energy flow is altered
dependence on human interference and inputs increase
What are some options and alternatives available for adding the benefits of diversity to the agricultural landscape?
1. adding new species to existing cropping systems
2. reorganizing or restructuring species already present
3. adding diversity-enhancing practices or inputs
4. eliminating dieversity-reducing or diversity-restricting inputs or practices
A primary and direct way of increasing alpha diversity of an agroecosystem
grow two or more crops together in mixtures that allow interaction between the individuals of the different crops
Intercropping is a form of multiple cropping - adds temporal diversity through sequential planting of different crops during the same season, the presence of more than one crop adds horizontal, vertical, structural and functional diversity
Strip cropping
plant different crops in adjacent strips
creates a "polyculture of monocultures"
increases beta diversity instead of alpha diversity
presents fewer management and harvest challenges than multiple cropping
What are some benefits from planting trees or shrubs around the perimeter of fields, along pathways of a farm or to mark boundaries?
protection from wind
exclude or enclose animals
produce tree products (firewood, construction materials, fruit, etc.)
Cover crop
a noncrop species planted in a field to provide soil cover, usually in between cropping cycles
Rotations
usually involve planting different crops in succession or in a recurring sequence
the greater the differences between the rotated crops in their ecological impact on the soil, the greater the benefits of the method
Fallows
a variation on the rotation practice
leave the land uncultivated or fallow
allows soil to "rest" - involves secondary succession and recovery of diversity in many parts of the system (esp. the soil)
What impact can animal activity have on the agricultural landscape?
activity such as grazing, crop residue consumption and manure deposition can alter aspects of structural divesity, species dominance and system function
What are the two components of species diversity?
Species richness - the number of species
Species evenness - the evenness of the distribution of the indviduals in the system among different species
What are some examples of importance values for a particular species?
number of individuals
biomass
productivity
Margalef's index of diversity
Measures number of species in terms of number of individuals
diversity= (s-1)/logN
(S is number of species, N is number of indviduals)
limited because it can't distinguish the varying diversity of systems with the same s and N
Shannon index
an application of information theory, based on the idea that greater diversity corresponds to greater uncertainty in picking at random an individual of a particular species
Simpson index of diversity
the inverse of an index of community dominance
Based on the principle that a system is most diverse when none of its component species can be considered any more dominant than any of the others
