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Agroecology > FINAL2Biotic interactions+Tillage > Flashcards

FINAL2Biotic interactions+Tillage Flashcards

0
Q

Biotic Interaction

indirect

A

organism changes the environment of another organism

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1
Q 
Biotic interactions
(direct)
A

organism directly affects another organism

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2
Q

removal interference -

A

removes a resource, such as light, water, nutrients etc.

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3
Q

additive interference -

A

adds something to environment that negatively affects another organism

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4
Q

facilitation–

A

adds something to the environment that positively affects another organism

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5
Q

Classification of interactions

A

Defined by:

whether impact of one species on another is +ve, - ve, or neutral

whether relationship is obligate or not

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6
Q

Competition

A

Direct interaction
e.g. animals fighting for territory

Indirect through removal interference
e.g. plant roots removing water/nutrientsor leaves shading other leaves

Within a single species
intraspecific competition
Between species
interspecific competition

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7
Q

Competition in agroecosystems

A

Intraspecific and interspecific competition - affects optimal planting densities for crop

close spacing increases intraspecific competition, but decreases interspecific competition with weeds

TRY TO MINIMIZE INTERSPECIFIC COMPETITION BETWEEN CROPS IN MULTIPLE CROPPING SYSTEMS

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8
Q

Multiple Cropping

A

Often a means of increasing diversity in agroecosystem
General term: - growing two or more crops in a year - need to consider both time and space
time dimension:
term can refer to:
two or more crops of same crop in a year - no diversity benefits
rotation between two or more different crops - get some diversity benefits
no inter-crop competition

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9
Q

Multiple cropping (contd

A

Multiple crop in space = intercropping
can be mixed, strip or row intercrops
will have inter-crop competition for some or all of crop cycle
degree of inter-crop versus intra-crop competition varies with design
mixed>row>strip

Multiple crop in time and space
= relay cropping

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10
Q

Mechanisms of intercrop interactions

A

Competition – limit between intercrops

Facilitation – if one crop benefits from presence of the other
E.g. planting legume with cereal

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11
Q

How to measure intercrop performance ?

A

Generally evaluating relative to use of monocropping

basic method involves measuring relative yields - does the intercrop “overyield” or “underyield” or give similar yields as monocrop system.

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12
Q

Land Equivalent Ratio

A

Most common measure used
Calculate using equation:
LER = Pcorn +Pbean Mcorn Mbean
where P = yield of crop in intercrop system
and M = yield of crop grown in monoculture

if LER > 1 —- have overyielding
if LER< 1 —– have underyielding

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13
Q

LER example

A

Monocrop yields: Intercrop yields
corn = 10 ton/ac 8 ton/ac
beans = 10 ton/ac 4 ton/ac
squash = 5 ton/ac 1 ton/ac

LER = 8 + 4 + 1 = 1.4
	     10  10   5
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14
Q

Other considerations

A

Total yield may not be most critical to a farmer
yield of a particular crop may be most important in which case the relative yield of that crop in the intercrop must be close to or >1

i.e. Pcorn > or = Mcorn

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15
Q

Other considerations…

A

Quality of crop important:
use marketable yield in LER calculation, i.e.total yield minus amount damaged
if price varies with quality categories then need to calculate “Relative value total” or RVT (see below)
If economic income important also need to calculate RVT

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16
Q

Relative Value Total

A

RVT = (aPcorn + bPbean)
aMcorn

where a= price of corn
b= price of beans
P = yield in intercrop, M = yield in monocrop
and a>b, corn price higher than bean price
note:
if bean price higher than corn, then bMbean would be used as denominator

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17
Q

Accounting for reduced input costs

A

If by using an intercrop you reduce or eliminate the need for any purchased input, then can modify RVT to account for this - known as RVI or relative value of intercrop

RVI = (aPcorn + bPbean)/(aMcorn - C)
where C = cost of extra inputs used in monocrop

18
Q

Problems with all these measures

A

How do you know you are making the most appropriate comparison?

Do you have the optimal mixture?
Are you comparing against the optimal monocrop system?
Are you skewing results by choice of varieties used?

19
Q

Optimal mixture?

A

What ratio of the component crops provide best performance?

What is the optimal planting density of the monocrops and the intercrops?

How could planting densities and ratios affected the results from the class intercrop study

20
Q

Mutalism

A

obligate relationship
rhizobium/legume
root/mycorrhizae
bees/plants pollination?

21
Q

Protocooperation

A

Protocooperation - not obligate

Cowbirds picking insects off cows

Both are examples of symbiosis

22
Q

Pollination services

A

The US Fish and Wildlife Service lists over 50 pollinator species as threatened or endangered
Wild bee populations have dropped 25 percent since 1990
Habitat loss a major issue, also pesticides
Tremendous economic impact when coupled with hive deaths in commercial honey bee colonies
Pollination services worth around $8 billion annually

23
Q

Commensalism

A

One species is helped by presence of another, but the other species is unaffected

Ecological examples include “nurse plants” and epiphytes

Agroecological examples include shade trees, windbreaks etc, and the epiphytic crop Vanilla fragrans

24
Q

Barley windbreaks

A

example of a “nurse crop”(barley also used as “nurse crop” for establishing alfalfa)

25
Q

Ammensalism

A

When one species is harmed by presence of another species, but the other species is unaffected.

Allelopathy is an example

26
Q

Parasitism

A

Host not usually killed

27
Q

Predation

A

Host killed and consumed

28
Q

Parasitoids

A

Important natural enemy- component of biological strategies for many crops
Typically kill their host

29
Q

Predation

A

use of natural enemies like predators of crop pests central to biological control efforts
lady beetles

30
Q

Herbivory

A

Eating of plant parts by herbivores

Example of removal interference

Not always negative - e.g. pasture management

31
Q

Tillage as a soil disturbance

POSITIVES

A

creates a good seed bed
aerates up layer of soil
kills weeds

32
Q

Tillage as a soil disturbance

NEGATIVES

A

Disruption of soil aggregates
exposing organic matter to microbial attack
reducing soil fertility
creating poor tilth leading to greater need for tillage
Vulnerable to erosion while field bare

33
Q

Tillage Disturbance Regime

FREQUENCY

A

usually more than 1x per year

34
Q

Tillage Disturbance Regime

SCALE

A

Field or farm scale

35
Q

Tillage Disturbance Regime

INTENSITY

A

Variable,often quite intense

36
Q

Tillage (con’t)

A

Moldboard Plow (Thomas Jefferson’s design, improved by Deere by using steel)
Turn soil over, burying crop and weed residue
Bury weed seeds
Aerate soil
Release nitrogen from SOM
improve seed bed

37
Q

As a uniformly applied technique, the moldboard plow has some distinct disadvantages:

A 
Loss of soil fertility
Create a plow pan
Destroys soil structure
Soils are vulnerable to wind and water erosion
Loss of S.O.M. and carbon storage
Loss of soil moisture
38
Q

Other types of tillage

A

Less aggressive soil disturbance - disks, spaders, and seed bed preparation implements
Implements to break through the compacted “plowpan”
Cultivation implements to remove weeds

39
Q

Ecology of Conservation Tillage

A

Reduced tillage practices vary with climate, soil type, and cropping system.
improves soil structure
protects soil from wind and water erosion
can increase soil organic matter
changes soil biology - increased fungal population at surface, and more earthworms

40
Q

Limitations in Conservation Tillage

A

Poor plant establishment
Weed problems usually increase:
so herbicide use is often high.
Macropores develop over time (worm burrows etc):
increases leaching of pesticides (especially herbicides) and nitrates.
Bed temperatures may be lowered:
slows seed germination and seedling growth.
Soil Chemistry may be altered detrimentally:
e.g. decrease pH in surface soil

41
Q

Conservation tillage

A

No-till or Strip-till (NT): A tillage/planting system where the soil is left undisturbed from harvest to planting except for nutrient injection. Planting is accomplished in a narrow seedbed or slot created by coulters, row cleaners, row chisels or roto tillers. Weed control is accomplished primarily with herbicides. Less than 25% row width disturbance is considered no-till.

Ridge-till (RT): A tillage/planting system where the soil is left undisturbed from harvest to planting except for nutrient injection. Planting is completed in a seedbed prepared on ridges with sweeps, disk openers, coulters, or row cleaners. Residue is left on the surface between ridges. Weed control is accomplished with herbicides and when ridges are rebuilt during cultivation.

Mulch-till (MT): The soil surface is disturbed prior to planting. Tillage tools such as chisels, field cultivators, disks, sweeps or blades are used. Weed control is generally accomplished with herbicides and/or cultivation.

42
Q

Conservation tillage

New equipment needed:

A

No-till planter or transplanter

Specialized ridge tillage implements

43
Q

Soil C sequestration?

A

Somewhat controversial

Increase C in shallow depths but not at deeper depths relative to conventional tillage – net effect?

Agroecology (11 decks)

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