exam 2
Why is it important to have many (abundant) diverse types of organisms living in the soil?
1) the more species are present in an agroecosystem, the less likely crop damage is to occur 2) different populations keep one another in check through predator-prey balance. 3) Different types of organisms perform different ecosystem functions... e.g. some are decomposers, some are predators, some are herbivores, etc. I didn't mention it in class, but the more ecosystem functions that are filled, the more efficiently energy is used in that system. Another way to think about it is that fewer resources are wasted.
What are three crop characteristics that can be used to group crops into rotational units?
Crop botanical family Crop rooting depth Crop nutrient demands Crop pest/disease complexes
Aside from making an agricultural ecosystem more resilient to disturbances, what are some other reasons that biodiversity is helpful in agriculture?
A diverse collection of organisms plays several roles in agriculture, including: Nutrient cycling (recycling organic matter - think the nitrogen cycle) Detoxifying or breaking down contaminants Biological pest control Pollination
Despite all of these benefits, cover crops can cause problems if not managed properly. Please describe two possible problems associated mis-managed cover crops.
Allowing cover crops go to seed-may become weedy/pest problem Cover crops may provide a safe refuge for insect pests Improperly seeded cover crops may fail to suppress weeds Weeds may become established within a cover crop stand and go to seed without the grower needing them When intercropping cover crops, problems with competition for resources such as water and sunlight may occur
What is a "green manure" cover crop? What characteristics should a good green manure crop have?
Already covered
Why is biodiversity useful in an agricultural ecosystem?
Biodiversity in an ecosystem makes that ecosystem better able to cope with change - the existing resources in the ecosystem are used more efficiently, more ecosystem functions and niches are being filled, and the ecosystem is more resilient to disturbances (physical, biological, environmental, chemical, etc.)
What is the difference between a cash crop and a cover crop? What are some reasons that a farmer might choose to plant a cover crop? Are there any drawbacks to cover cropping?
Cash crops are planted in order to be harvested (grains, vegetables, fruits, hay, etc), whereas cover crops are planted for other purposes, primarily to build the soil. Reasons to plant cover crops are primarily to prevent soil erosion, to "catch" nutrients and prevent leaching, and to build soil fertility - but they can also be used for other purposes such as biofumigation. Drawbacks are that cover cropping adds expense (seeds, management time), and that when cover cropping, the land cannot be used for cash crops. If not managed properly (tilled before setting seeds), the cover crop can become a weed or can increase weed problems.
What is compost?
Compost is a biologically stable material that results from decomposition of organic residues
When building a compost pile, why would someone need to know the carbon to nitrogen (C:N) ratio of the starting materials?
Composting (especially hot composting) relies on thermophilic (heat-loving) bacteria. Bacteria require their "diet" to be roughly 25-30:1 C:N. If there is excess Carbon, the bacteria will not be able to completely break down the raw ingredients. If there is excess Nitrogen, the excess Nitrogen will be volatilized and released as ammonia (leading to a stinky compost pile).
Why would a farmer decide to compost her manure before she used it in her garden? Is there any drawbacks to doing this?
Composting kills plant pathogens, animal pathogens, and weed seeds that are found in manures. The farmer could use composted manure right away on her organic garden without worrying about food safety issues that could be a problem with raw manure. Composting also reduces odor and improves the texture of the manure. HOWEVER, drawbacks are that much of the nitrogen found in manure is lost during composting, and the process of composting can be quite time-consuming.
List and describe several strategies that farmers might use to conserve their soil resources; e.g. prevent erosion.
Contour planting - crops are planted in strips perpendicular to the slope on a field Terracing - crops are planted in narrow level areas that are created on very steep hillsides Perennial crops - do not require tillage, so therefore hold the soil in place better than those which require that the soil be tilled up every year
Crop rotation provides some of the benefits of a polyculture system as well as some of the benefits of a monoculture system. Explain what crop rotation is, and list at least 3 reasons that crop rotation is a good idea.
Crop rotation is a planned system of growing different crops in succession on the same piece of land. Rotation provides some of the benefits of polycultures: increased biodiversity, yield stability and more efficient and complete use of resources, but usually only over time - not within a growing season. (Note - It doesn't give much protection against crop failure within a given year!). Within a growing season, a crop in rotation can be grown as a monoculture. The primary benefit is ease of management because of uniform crop needs, harvest time, and growth habit.
For each of the following plant families, list at least 2 crops that belong to that family.
Cucurbitaceae: SEE notes, guide at back of packet Poaceae: Brassicaceae: Asteraceae: Alliaceae Apiaceae: Rosaceae: Solanaceae: Fabaceae:
If we think of the soil as a pool of available nutrients for plant growth, what are the processes by which nutrients are added to, and subtract nutrients from the pool?
Gains: fertilizers, nutrient fixation, microbial decomposition, weathering Losses: plant uptake, volatilization, erosion, nutrient fixation, and leaching
Please name three different forms in which carbon is encountered in agroecosystems.
Gaseous form CO2 In living plant tissue and carbohydrates (e.g., glucose C6H12O6) In organic matter-decomposing or decomposed (humus) Mineralized carbon-coal, graphite, diamonds
How would you describe a soil that is "healthy" from a biological, physical, and chemical perspective?
Healthy soils are ones with: abundant and diverse living organisms (biologically healthy) plenty of nutrients required by plants (chemically healthy) well-aerated with plenty of pores (physically healthy)
What rules do certified organic farmers have to follow if they use 'raw' animal manures? What's the reasoning behind these rules?
If they use raw manure, they can only use it on non-edible or perennial crops, or at least 60 days before harvest on edible crops like vegetables. Composted manure can be used at any time. They also have to provide a plan for how they will apply and use manure in a way that doesn't contaminate waters with bacteria or nitrates.
Explain the difference between an overlap planting of two crops and planting a mixture of the same two crops. What are the advantages of each?
In an overlap planting, the two crops would overlap for some part of their life cycles. In a mixture, the two crops would be planted together, and would overlap for their entire life cycles. Mixtures increase crop biodiversity throughout the entire growing season, conserve water and nutrient resources. The two crops might complement one another (increasing total production season or increasing total yields), or might be antagonistic or compete for resources. Overlap planting minimizes some of the competition that can occur in mixtures, and therefore often provides better yields.
Why can increased salinity due to over-fertilization cause problems for plants' ability to uptake water?
Increased salinity may cause interference with the osmotic gradient that encourages water to move from soil (high water potential) towards the roots (inside of roots should have lower water potential due to higher solute concentration). Water moves from areas of high water potential to areas of low water potential. If the solute concentration outside of the roots increases to levels higher than those found inside of the roots, the needed concentration gradient is no longer in place and water does not move as effectively from the soil towards the root hairs where it can be uptaken by the plant
How does 'finished' compost different from the feedstocks (aka the starting materials)?
It's already decomposed, nutrients are in a more stable (and less available) form, pathogens & weed seeds are killed, it has a finer texture, and smells and weighs less.
What are some ways that farmers promote or limit biodiversity on their farm?
Limit: monocultures (low levels of "planned biodiversity") frequent disruption of habitats broad-spectrum pesticides Promote biodiversity: Varied land use near fields (hedgerows, woodlands etc) Beneficial insectaries Use organic sources of nutrients that require microbes to break them down Plant many types of crops
Are crop farms, livestock farms, or integrated (crop plus livestock) farms more likely to end up accumulating nutrients because nutrient IMPORTS exceedEXPORTS? Why is this important?
Livestock farms tend to accumulate nutrients because a large amount of nutrients end up staying on the farm as manure. Crop farmer tend to have a nutrient deficit because most nutrients are exported off the farm as crops. Integrated farms are more likely to be able to balance nutrient inputs and output nutrient
Name two reasons why many organic vegetable farms have overly high levels of phosphorus in their soils.
Many organic farmers fertilize with manure. Manure has similar levels of N and P. Most farmers fertilize based on crop nitrogen needs. Crops use far lees N than P so by fertilizing with manure one is applying P at a rate beyond which plants can use. Solutions-switch to a fertilizer with low P for some time like blood meal or soybean meal.
Where in the soil profile are most of the soil biota found?
Most are found in the top 10-15 cm of soil, or the top 4-6 inches.
Why might use of an organic fertilizer promote more soil biodiversity than a highly soluble conventional fertilizer would?
Organic fertilizers require microorganisms to mineralize the nutrients found in the fertilizer. Synthetic fertilizers contain readily available form of plant nutrients-do not require any microbes to make them available. The organic fertilizers create distinct niches which will be occupied by a diverse mix of soil microbes.
What is Soil Organic Matter, and why is it considered important and beneficial?
Organic matter is the sum total of the dead, decomposing, and completely decomposed organisms in the soil. Decomposing OM provides food for living soil organisms. As it is broken down, it produces sticky substances which promote aggregation and good soil structure, which in turn helps water infiltration and water-holding capacity. Stable decomposed organic matter particles have high cation exchange capacity (CEC), which means they are hold plant-available nutrients well.
Nitrogen (and all other elements) exist in many forms within the environment. List at least 4 forms of Nitrogen found in the environment. For each, tell whether plants can use that form directly. *you should understand the nitrogen cycle completely* (e.g., immobilization, mineralization, nitrification, denitrification, volatilization) Which form is most prone to leaching?
Organic nitrogen - this is nitrogen that's part of organic compounds within living plants and animals (like amino acids, DNA, etc). It is not available for plants until it is decomposed and broken down. Inorganic forms of nitrogen include: Nitrogen gas (N2) - found in the atmosphere, not available for plants to use Nitrate (NO3) -found in soil, is useful for plants Nitrite (NO2) -found in soil, not stable Ammonium NH4 -found in soil, is useful for plants (a few plants take it up directly, but most require that it be converted by microbes into NO3 first) Ammonia NH3 - this is a volatile gas, not taken up by plants
Name three reasons why knowing botanical families is useful for practitioners of sustainable agriculture
Plants of the same botanical family tend to be prone to the same types of pest and disease problems so this information can help you plan effective rotations You can recognize closely related wild growing plants which may serve as alternate hosts for insect pests or plant pathogens Crops in the same family tend to have similar soil nutrient needs By knowing the major pests and diseases for a particular plant family will help you in pest/disease identification
Define polyculture. List the advantages and disadvantages of polyculture, as compared with monoculture.
Polyculture = the cultivation of more than one crop species on the same piece of land in various temporal and spatial patterns (over time and space) Advantages: slows spread of pests, more stable yield, insurance against crop failure of one crop, resources in the ecosystem are used more efficiently Disadvantages: complicated agronomic management, more host species may mean more pests and diseases at any one time. (The advantages tend to outweigh the disadvantages!).
What are the two primary factors which determine the water potential of water inside of plants?
Pressure potential-can be positive or negative. Positive in case of turgid plant cell. Negative in case of xylem. Solute potential-The amount of dissolved solutes found in the water. Always makes water potential more negative (lower)
List and briefly describe advantages and disadvantages of reduced tillage systems.
Pros: o Avoiding tillage reduces leaching and erosion o Tillage that incorporates oxygen into the soil speeds up the decomposition of organic matter; reduced tillage systems maintain organic matter better than conventional tillage systems o If you can reduce the number of times that you need to operate equipment on the field, it will save fuel and time Cons: o Need specialized equipment (like no till seeders or transplanters) o Usually need herbicide (because it is important to kill weeds that will compete with the crop) o These systems are vulnerable to compaction because of heavy equipment driving on them, without loosening the soil with intermittent deep tillage. o It is hard to add fertilizers and amendments to these systems o The presence of cover crop residue on the soil surface cools the soil, which can be a disadvantage in cool climates.
The soil bacterium Rhizobium is a very important soil microorganism in agricultural soils. What does it do, and why is it so important?
Rhizobium is a soil bacterium that infects the roots of Legume plants (family Fabaceae) in a symbiotic relationship. Infected roots make nodules around the bacteria. Within the nodules, the bacteria convert atmospheric nitrogen (N2 gas) into nitrate that the plants can use, and they use as food the carbohydrates produced by plants. Without Rhizobium, legume plants would not fix nitrogen.
What happens to pesticide residues on materials that are composted?
Several things happen. The fate varies, depending on which pesticide you are talking about. Some pesticides are mineralized to produce inorganic compounds. Others are partially degraded to form secondary compounds. Some are bound tightly to (or complexed with) humus particles. Yet others are lost, through volatilization, leaching, etc. A few don't break down quickly and are concentrated during composting because they are persistent in the environment.
What is sewage sludge, and why is its use as an agricultural amendment considered controversial (and not allowed in organic systems)?
Sewage sludge is the untreated residue that's left over after processing human waste in a sewage treatment facility. While it is normally processed to kill any human pathogens, sewage sludge contains all of the things that go down household and industrial sewage systems. This includes some items that can be concentrated if applied to agricultural lands: pharmaceuticals, heavy metals, radionuclides (radioisotopes), etc.
Why are microbes an important part of the nitrogen cycle? List at least three functions microbes perform in the nitrogen cycle.
Some microbes mineralize N (convert it from organic to inorganic forms) as they decompose organisms, by ammonification and nitrification. Some microbes fix N (convert it from N2 gas to inorganic nitrogen). As microbes use N themselves, they immobilize N (convert in into an organic form). The process of nitrification is carried out by microbes
Define the following terms, which describe interactions between organisms in an ecosystem: symbiosis or mutualism, competition, antagonism, and parasitism. Be able to provide an example of each one
Symbiosis/Mutualism - a mutually beneficial relationship Competition - demand by at least 2 organisms for limited resources Antagonism - Inhibition of or interference of a substance or organism by another Parasitism - one organism receives benefits from another by directly causing damage to it.
If you had a choice between a two-year rotation (lettuce-tomato-lettuce-tomato) and a four-year rotation (lettuce-tomato-bean-onion), which would you choose and why?
The four-year rotation is better, for several reasons: -more time between similar crops, better chance of avoiding disease problems -less soil depletion because different crops place different demands on the soil -more crops are grown, so more biodiversity
How does a catch crop differ from a green manure crop?
The goal of a catch crop is to catch any excess fertilizer left over in the fields after harvesting a cash crop. This has both economic and environmental benefits. Rather than leaching or eroding from the field, plant nutrients elft over from fertilizer application can be take up into the biomass of the cover crop. When that cover crop is killed and incorporated into the soil, some of those nutrients will be mineralized and then be available for plant uptake by subsequent crops. A green manure crop is one that is grown for the purpose of incorporating it into the soil to increase the soil organic matter. It is being used as a soil amendment. A good green manure crop would have a lot of biomass (e.g be a BIG plant), fix nitrogen (e.g. be a legume), and would grow quickly to suppress weeds.
Why is it important to incorporate (till in) raw manure after spreading it (applying it to the field)? Give at least three reasons.
To avoid loss of nutrients due to volatilization and leaching, to avoid contamination of surface waters with nitrates and bacteria, to make sure that it's where the plants need it and can access it, maybe to reduce odors...also food safety
What does it mean to 'turn' a compost pile, and why is it necessary?
Turning just means mixing the pile up. It is necessary because the bacteria need oxygen as well as the carbon and nitrogen found in the raw starting materials. Turning evenly distributes the oxygen found on the outside of the pile and the heat that builds up on the inside of the pile - both oxygen and heat are needed for effective decomposition.
For each of the following compost 'feedstocks', indicate whether it has a C:N ratio that is much lower than 30:1, or much higher than 30:1.
Vegetable wastes - lower Straw - higher Fresh chicken manure - lower Fresh pig manure - lower Sawdust - higher Corn stalks - higher Grass clippings - lower Paper - higher *note that you can find a list of several common feedstocks and their C:N ratio in the reading.
Define the concept of water potential. Describe the water potential gradient that occurs from the soil through the plant and out through the plants stomates.
Water potential refers to the amount free energy water contains. Water potential has a maximum value of zero-This is pure deionized water held at a set elevation. This pure water has the maximum ability to do work (for example ability to dissolve solutes). Anything that is done to that water such as adding solutes, or attaching that water to soil particles will make water potential increasingly negative. Water moves from areas of high water potential to areas of lower water potential. When a soil is very wet (saturated), water potential may approach zero. There is a continuum of decreasing water potential that takes place from soil-into root hairs-into xylem-into leaves-out leaves stomata as water vapor. The water potential of the water in the air is very low. This continuum keeps water moving through the plant in a continuous stream.
What are four possible benefits of using cover crops?
Weed suppression Building soil organic matter Increasing soil Nitrogen by using N fixing cover crops Biofumigation Nutrient mining Increasing farm biodiversity
