SAFS 502 midterm exam

describe two ways in which excess nitrogen in agroecosystems can be a problem for the environment

- leach out of the soil - contaminate water sources and cause algae blooms

phosphorus cycle

- phosphorus isn't very mobile (not prone to leaching) - can be lost through erosion - can't be synthesized, it must be mined - found in significant amounts, but only in a few large deposits scattered across the planet

what were the consequences of agriculture?

- population increase - sedentary lifestyle (permitted shorter birth intervals and the development of "technology") - social systems/ stratification - agricultural "expansion"

ruderals (C-R-S triangle)

- adapted to conditions of high disturbances and low stress - fast growing and rapidly complete their life cycles, and generally produce large amounts of seeds

competitors (C-R-S triangle)

- adapted to conditions of low stress and low disturbance - outcompete other plant by most efficiently tapping into available resources - rapid growth rate, high productivity, and high capacity for phenotypic plasticity

stress tolerators (C-R-S triangle)

- adapted to environments with high stress but low disturbance - often found in stressful environments (ie. alpine or arid habitats) - generally have slow growth rates, high rates of nutrient retentions, and low phenotypic physiological variability

how was the development and use of synthetic fertilizer a turning point in modern agriculture?

- agriculture is no longer reliant on biological sources of N - synthetic fertilizers can be added to the soil once nutrient supply is depleted - no need for careful management of nutrient cycling/recycling

Soil Organic Matter (SOM)

- an important sources of nutrients for plant growth - important in building, promoting, and protecting the soil ecosystem - key component of soil structure - water and nutrient retention - food source for soil microorganisms

stress/disturbance- intensity theory

- based on the premise that there are two factors that limit plant growth in any given area STRESS and DISTURBANCE -stress: limited nutrient/ resource availability - disturbance: something that reduces biomass or kills individuals

strategies for improving agricultural nitrogen management

- rotational complexity to conserve N (e.g., cover crops during periods between cash crops) - soil testing - fertilizer timing, placement, and formulation - watershed level strategies for mitigation excess N (e.g., perennial strips) - better management of manure

directed selection

intentional manipulation of a population's genetic material

how might C be partitioned within the biotic pool?

into trophic levels

how might terracing improve the sustainability of agriculture in these environments?

terracing farming can help reduce soil erosion and water runoff

carrying capacity

the population size that can be supported in a given area based on given "quantity" of limiting resources

what was the environmental constraint that led to terraced agriculture?

topography- very steep and mountainous landscape that caused an increase in erosion

life history strategy

unique set of adaptions that allow a species to maintain a population in an environment over time

uptake (assimilation)

uptake by plants of N in soluble and biologically available forms. N that has been assimilated by plants is no longer available to microbes or subject to leaching

nitrogen immobilization

uptake of microbes of N in soluble and biologically available forms (amino acid, NH4, and NO3) immobilized N is no longer available to plants or subject to leaching

r-selected species

-live/evolve in harsh or variable environments - high intrinsic growth rate - allocate more energy to reproduction than to growth and maintenance - limited more by physical factors rather than biotic factors - colonizers

K-selected species

-live/evolve in stable environments - mortality is more a function of density dependent factors (can live at or near carrying capacity - low intrinsic growth rate - allocate more energy to growth and maintenance than to reproduction - limited by biotic factors than physical

what are some of the important populations one might find in an agricultural system?

1. crop plants (including cover crops) 2. harmful and beneficial pests 3. weeds 4. soil dwelling populations

why were so few species domesticated?

1. diet too restrictive 2. growth rate and birth spacing 3. dangerous behavior 4. reluctant to breed in captivity 5. lack of dominance hierarchies 6. tendency to "panic" in captivity

stages of colonization

1. dispersal 2. establishment 3. growth and maturation 4. reproduction

why is the loss of crop genetic diversity in acroecosystems a cause for concern?

1. genetic diversity provides the material for directed selection/breeding (disease resistance, pest resistance, drought tolerance) 2. food security 3. supports higher trophic levels 4. loss of farmer control (shifts away from farmers to large multinational companies)

directed selection approaches

1. mass selection- collection of seeds from individuals with useful traits (takes a while, but preserves genetic diversity) 2. classical breeding- includes development of hybrids and high yield varieties 3. transgenic modification- genetic engineering

nitrogen fixation

Process of converting nitrogen gas into ammonia can be conducted biologically, through the action of N2 fixing microbes, or industrially

why did agriculture arise where it did?

agriculture arose where the most numerous and valuable domesticable wild plant and animal species were native

what is the current global population?

approximately 7 billion people

of the 200,000 known species of plants, only about ____ of those species have been domesticated a. 14 b. 100 c. 500 d. 900 e. 5,000

b. 100

between 1830 and 1885, approximately what percentage of the land in New England was in some form of agriculture? a. 7% b. 25% c. 50% d. 90% e. 100%

c. 50%

extensification of agriculture in New Hampshire (and NE in general) would involve ______ and would likely lead to _______ a. increasing production on current land; a reduction in forest cover b. increasing production on current land; an increase in forest cover c. bringing more land into agricultural production; a reduction in forest cover d. bringing more land into agricultural production; an increase in forest cover

c. bringing more land into agricultural production; a reduction in forest cover

Nitrification

conversion of ammonium to nitrate

which of these processes is dependent on soil microbes? a. decomposition of labile organic matter to recalcitrant organic matter b. nitrogen mineralization c. conversion of ammonium to nitrate d. all of the above e. none of the above

d. all of the above

when intercropping (ie. growing two crop species in the same place at the same time), it would make agroecological sense to choose two crops that ________. a. occupy very similar niches b. acquire resources in the same matter c. are weak competitors against weeds d. occupy different niches

d. occupy different niches

in 1935, there were about 6.8 million farms in the US. Currently there are approximately _____ farms, and the majority of US farmland is in _____ scale farming operations a. 2 million; medium b. 5 million; large c. 2 million; small d. 8 million; large e. 2 million; large f. 8 million; small

e. 2 million; large

C:N ratio

low C:N (labile organic matter) is good for short term retention/soil quality high C:N (recalcitrant organic matter) decompose more slowly and is good for long term retention/ soil quality

do you think SOM levels are (in general) higher or lower in our region than they were in the early 1800s?

probably higher due to afforestation since agricultural abandonment

which biotic pool likely contains the most C? which biotic pool likely contains the least?

producers contain the most C carnivores (higher trophic levels) contain least C

how might the biotic pool be subdivided?

producers, primary consumers, secondary consumers, etc.