FINAL2Biotic interactions+Tillage Flashcards
Biotic Interaction
indirect
organism changes the environment of another organism
Biotic interactions (direct)
organism directly affects another organism
removal interference -
removes a resource, such as light, water, nutrients etc.
additive interference -
adds something to environment that negatively affects another organism
facilitation–
adds something to the environment that positively affects another organism
Classification of interactions
Defined by:
whether impact of one species on another is +ve, - ve, or neutral
whether relationship is obligate or not
Competition
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
Competition in agroecosystems
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
Multiple Cropping
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
Multiple cropping (contd
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
Mechanisms of intercrop interactions
Competition – limit between intercrops
Facilitation – if one crop benefits from presence of the other
E.g. planting legume with cereal
How to measure intercrop performance ?
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.
Land Equivalent Ratio
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
LER example
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
Other considerations
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
Other considerations…
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
Relative Value Total
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
Accounting for reduced input costs
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
Problems with all these measures
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?
Optimal mixture?
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
Mutalism
obligate relationship
rhizobium/legume
root/mycorrhizae
bees/plants pollination?
Protocooperation
Protocooperation - not obligate
Cowbirds picking insects off cows
Both are examples of symbiosis
Pollination services
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
Commensalism
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
Barley windbreaks
example of a “nurse crop”(barley also used as “nurse crop” for establishing alfalfa)
Ammensalism
When one species is harmed by presence of another species, but the other species is unaffected.
Allelopathy is an example
Parasitism
Host not usually killed
Predation
Host killed and consumed
Parasitoids
Important natural enemy- component of biological strategies for many crops
Typically kill their host
Predation
use of natural enemies like predators of crop pests central to biological control efforts
lady beetles
Herbivory
Eating of plant parts by herbivores
Example of removal interference
Not always negative - e.g. pasture management
Tillage as a soil disturbance
POSITIVES
creates a good seed bed
aerates up layer of soil
kills weeds
Tillage as a soil disturbance
NEGATIVES
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
Tillage Disturbance Regime
FREQUENCY
usually more than 1x per year
Tillage Disturbance Regime
SCALE
Field or farm scale
Tillage Disturbance Regime
INTENSITY
Variable,often quite intense
Tillage (con’t)
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
As a uniformly applied technique, the moldboard plow has some distinct disadvantages:
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
Other types of tillage
Less aggressive soil disturbance - disks, spaders, and seed bed preparation implements
Implements to break through the compacted “plowpan”
Cultivation implements to remove weeds
Ecology of Conservation Tillage
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
Limitations in Conservation Tillage
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
Conservation tillage
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.
Conservation tillage
New equipment needed:
No-till planter or transplanter
Specialized ridge tillage implements
Soil C sequestration?
Somewhat controversial
Increase C in shallow depths but not at deeper depths relative to conventional tillage – net effect?
