Urban Farm Final Examination Study Guide
Fall 2008
Soil Health and composition
 The rhizosphere is the zone around the roots
 Dirt is lifeless, but soil is made up of air, water, minerals and organic matter that allow
microorganisms to thrive
 Ideal garden soil is made up of 25% air, 25% water, 45% mineral matter, and 5% organic matter
25% air
45%
mineral
matter
25%
water
5%
organic
matter
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The mineral slice is made up of three kinds of mineral particles: sand, silt, and clay
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Sand particles, the largest of the three, are coarse, hard, and round. They don't hold water or nutrients,
but they do help aerate the soil.
Silt particles are finer than sand, but still somewhat gritty (like talc powder).
Clay particles are nearly invisible to the naked eye, but their flat shape allows them to pack tightly
together with very little air space. Clay soil can make growing vegetables difficult because it does not
drain and does not allow air to penetrate to the rhizosphere
Loam is an ideal mixture of sand (40%), silt (40%) and clay (20%)
Compost or humus is organic matter in a purposeful state of decomposition; we add this to our beds to
improve their tilth and promote the growth of beneficial microorganisms
In the Willamette Valley (as elsewhere), the most fertile agricultural soil is closest to the river, a result
of the Willamette River's past weaving and flooding
The N-P-K numbering on bags of fertilizer refers to nitrogen (N), phosphorus (P), and potassium (K)
Nitrogen is essential to the production of proteins and the growth of dark, green leaves
(photosynthesis).
Phosphorus promotes development of stem, flower, fruit and root. It also promotes plant vigor and
disease resistance.
Potassium is balances nitrogen and phosphorus and is good for all around plant health.
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Calcium builds strong cell walls and promotes the growth of beneficial bacteria
Synthetic fertilizer can be cheaper and stronger, but it does not contain the trace nutrients upon which
plants depend and can make the soil inhospitable to beneficial soil microorganisms such as fungi and
bacteria. Organic fertilizer is better for the soil food web and increases the soil's ability to retain
moisture, in addition to being the more environmentally responsible (sustainable) option.
Soil pH is a measure of the acidity of the soil; ideal pH is between 6.25 and 6.75 on a scale of 0-14
(with 0 being the most acidic and 14 being the most basic). Soil that is too acidic cannot take up the
nutrients needed for plant growth. Our Willamette Valley soil typically has a pH of around 6, so we
make it more basic by adding lime to our fertilizer.
At the Urban Farm, we keep our soil in good tilth without pesticides or synthetic fertilizers by
building raised beds with clear paths so we don't compact the soil; we add compost (humus) to
improve soil structure and feed micronutrients; we also add mulch (straw, leaves, compost) to
suppress weeds and increase organic matter in the soil; we increase soil fertility with organic fertilizer;
we use cover crops to increase fertility and add organic matter; we use crop rotation and plant a
mixture of crops to prevent nutrient depletion and break pest and disease cycles
Fall gardening practices and crops
 Fall crops on the farm include those that can withstand cold temperatures by growing thick leaves or
by growing mainly underground. These include: beets, carrots, broccoli, cabbage, garlic, onion, leeks,
fava beans, and kale. We may also grow more delicate greens such as lettuce and spinach in the
greenhouse or under a protective frame.
 Fall gardening practices to improve and maintain soil health and fertility:
o Cover cropping
o In situ composting
o Mulching pathways with leaves
o Protecting plants and bare soil from cold weather with cloches
o Adding organic matter such as compost, leaves and straw to help with drainage
o Restoring nutrients lost in the summer with compost, manure and/or organic fertilizer
o Rotating crops to break pest cycles
Cover Crops
 Reasons for cover cropping:
o Legumes such as field peas and fava beans help restore nitrogen to the soil
o Cover crops can be turned in in the spring to add organic matter to the soil
o Cove crops prevent erosion and loss of topsoil
o Cover cops hold in nutrients that could be lost to the rain
o Deep cover crop roots help break up hard pan and improve soil structure, drainage and water
penetration
 Types of cover crops:
o Fava beans
o Crimson clover
o Austrian field peas
o Hairy vetch
o Rye
o Winter wheat
Compost
 Benefits of compost in garden soil:
o Introduces beneficial microorganisms that can help control plant diseases
o Can help regulate soil pH and prevent fluctuations
o Provides micro- and macronutrients
o Improves soil structure, keeping soil in “good tilth”
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o Improves drainage and moisture retention
In order to gain enough heat to speed up biological and chemical reactions, a thermoyphilic compost
pile should be at least one yard square.
When a compost pile is too large, it becomes difficult to turn and it can begin to decompose
anaerobically because air is unable to penetrate to the center
Maggots in a compost pile indicate that your carbon to nitrogen ratio is off. Maggots are fly larvae
that thrive in nitrogen-rich conditions. Encourage more balanced compost fauna by adding more
“brown” matter to your pile, such as dry leaves, straw, or shredded newspaper
“In situ” or “sheet” composting is the process of composting organic matter directly into the soil, in
place, rather than in a thermophylic compost pile elsewhere. To compost in situ, chop plants that are
already growing in the beds and turn them in with compost, leaves/straw, and manure. Cover crop
with legumes to help maintain beneficial nitrogen levels.
It is important to maintain a balance of carbon to nitrogen in your compost pile. Sources of carbon
include “brown” materials such as dry leaves, straw, newspaper/paper, wood ash, and saw dust.
Sources of nitrogen include “green” materials such as kitchen scraps, green chop from the garden
beds, comfrey, grass clippings, manure, and comfrey.
Compost should be sufficiently “finished” before it is applied to beds. Unfinished compost continues
to draw nitrogen from its surroundings, and away from any plants that are trying to grow. Unfinished
compost may “burn” fragile plant roots as it breaks down.
Fungi and plants: Mycorrhizal fungi supply plants with water and nutrients in exchange for
carbohydrates and proteins. Fungi can also help repel disease-causing organisms.
Soil bacteria are at the bottom of the soil food chain and are responsible for the initial break down of
organic materials. When they are, in turn, consumed by micro-predators, nitrogen becomes available
to plants. Beneficial bacteria also create gums and gels that help soil become well-aggregated and stay
in “good tilth”.
Some definitions (Organic, Tilth, CSA)
 Community Supported Agriculture: CSA is a direct relationship between farmers and individual
consumers/community members, where both parties share in the risks and benefits of farming.
Consumers purchase a share of the farm’s harvest at the beginning of the season and receive weekly
deliveries of produce throughout the season. This helps farmers by ensuring a predictable income for
the year and helping with up-front costs.
 Organic (with a capital “O”): If a food is labeled “Organic”, this indicates that it has been certified to
meet USDA Organic standards by an official certifying body. Generally, this means it is a nongenetically modified organism grown without use of pesticides, chemical fertilizers, or growth
hormones (in the case of livestock). An Organic farm is one that has been certified by an official
body.
 Tilth (lower case t) refers to the state of aggregation of soil and its suitability for growing plants. Soil
that is in "good tilth" is well aggregated and crumbly, indicating that it is alive with beneficial bacteria
and fungi. Air, water, and plant roots can move freely through this soil.
 Tilth (upper case T), as in "Oregon Tilth Certified Organic", is the name of an internationally
recognized body that sets production standards and certifies organic food producers.
Plant Families
 Brassicas include:
o Cabbage
o Broccoli
o Mustard
o Cauliflower
o Kale
o Collards
o Kohlrabi
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o Radishes
o Arugula
o Turnips
Alliums include:
o Onions
o Leeks
o Garlic
o Shallots
Plants in the Solonaceae (nightshade) family include
o Tomatoes
o Potatoes
o Tomatillos
o Peppers
o Eggplant
Plants in the Umbelliferae family include
o Carrots
o Parsley
o Fennel
o Cilantro
o Celery
o Parsnips
o Dill
o Poison Hemlock
Plants in the Chenapodiacea family include
o Beets
o Chard
o Spinach
Plants in the Compositae family include
o Lettuce
o Sunflowers
o Artichokes
Plants in the Curcurbitaceae family include
o Squash (zucchini, pumpkins, etc)
o Cucumber
o Melons
o Watermelon
Plants in the Favaceae (legume) family include:
o Peas
o Beans
Some common weeds on the farm are:
o Quack grass
o Comfrey
o Morning glory
o Horsetail
o Apple mint
o Buttercup
o Himalayan blackberry
o Borage
Some hard-to-eradicate weeds:
o Quackgrass can regenerate from small pieces of root
o Morning glory has extensive roots and can regenerate from small pieces
o Apple mint can regenerate from small pieces of root or stem