Sustainable Agriculture Activity Guides

http://studentfarm.ucdavis.edu/edumat/saguides

Nitrogen fixation is the natural process, either biological or abiotic, by which nitrogen (N₂) in the atmosphere is converted into ammonia (NH₃).^[1] This process is essential for life because fixed nitrogen is required to biosynthesize the basic building blocks of life, e.g., nucleotides for DNA and RNA and amino acids for proteins. Nitrogen fixation also refers to other abiological conversions of nitrogen, such as its conversion to nitrogen dioxide.
Nitrogen fixation is utilized by numerous prokaryotes, including bacteria, actinobacteria, and certain types of anaerobic bacteria. Microorganisms that fix nitrogen are called diazotrophs. Some higher plants, and some animals (termites), have formed associations (symbioses) with diazotrophs. Nitrogen fixation also occurs as a result of non-biological processes. These include lightning, industrially through the Haber-Bosch Process, and combustion.^[2] Biological nitrogen fixation was discovered by the Dutch microbiologist Martinus Beijerinck.





 TEST:

http://www.bbc.co.uk/bitesize/quiz/q56103256

Nitrogen cycle

Grow Your Own Fertilizer

Cover crops have many potential benefits in agriculture. They can improve numerous soil physical, chemical, and biological characteristics, improve water retention and utilization, reduce erosion, control weeds, enhance biological control of pests and help manage crop nutrients, particularly nitrogen.
Nitrogen is a primary plant nutrient that is an important factor in determining a crop’s health and productivity. However, it can also be a financially and environmentally costly farming/gardening input. Synthetic nitrogen fertilizers can play a significant role in polluting our water and air resources, while also consuming a great deal of fossil fuel energy in their production and transportation to the farm. Cover crops can play an effective role in reducing the need for synthetic nitrogen fertilizers.
The goal of this activity is to introduce the idea that nitrogen can be produced and conserved on a farm biologically through the use of cover crops. In order to make good use of a cover crop in a farm’s nutrient management strategy, one needs to estimate how much nitrogen a mature cover crop contains. This estimate can then provide an approximate figure of how much nitrogen the cover crop will supply the soil reserve and
next season’s crop. The following reference resources are provided to improve your familiarity with the topic.
Resource References
Nitrogen Cycle. Kimball's Biology Pages, John W. Kimball
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/N/NitrogenCycle.html
Cover Crop Resource Page. UC Sustainable Agriculture Research and Education
Program (SAREP)
http://www.sarep.ucdavis.edu/ccrop/
Cover Crops for California Agriculture. Miller, P. R., W. L. Graves, et al. 1989.
University of California, DANR Publication 21471, Oakland CA

Introduction
Crops generally require more nitrogen than any other nutrient, usually between 80 and
200 lbs of nitrogen per acre. Encouraging nitrogen fixation via the mutualistic
relationship between legumes and associated Rhizobia bacteria is one of the most
important ways farmers can add nitrogen to the soil in sustainable farming systems.
However, it is important for farmers to know the amount of nitrogen that such a cover
crop contains and may supply to a subsequent crop. In this exercise, participants will
estimate the nitrogen content of a legume cover crop. They will harvest and weigh all of
the above ground biomass of a cover crop from a number of sample sites in the field.
These weights will then be used to estimate the amount of nitrogen in the cover crop.
Such information can be used by a farmer to help make decisions about when to mow
and/or turn a cover crop into the soil or how much additional nitrogen may need to be
supplied to the crop from other sources.

To Lead This Activity You Need to Know
• cover cropping
• the nitrogen cycle and its relationship to soil fertility management
• biological nitrogen fixation
• nitrogen requirements for common crops


Key Concepts
• nutrient cycles
• plant nutrition
• mutualism
• nitrogen fixation
• cover crop
• biomass
Objectives
• Engage participants in assessing the nitrogen contributing performance of a cover crop.
• Introduce the concept of mutualistic relationships in the context of agriculture.
• Demonstrate the economic and ecological benefits of biologically managed soil fertility.

Materials
• 3 ft x 3 ft (or for metric measurements, 1 meter x 1 meter) square quadrats, made
from wood, PVC pipe or similar material (1 per team of 3 – 4 students)
• hedge shears (1 - 2 shears per team)
• burlap or woven fabric bags and a method to label them (2 – 3 per team)
One of each per class:
• a scale or balance with the ability to measure full bags weighing 20 - 30 lb (or10-
15 kg) (note: if measuring a sample from an intercrop of legumes and grasses,
and the primary scale can not make measurements less than 1 pound, a second,
more sensitive scale is necessary)
• conversion factor chart (included below)
• calculator
Activity (45-50 minutes)
(The instructions and examples below use English units; however this exercise can be done using metric measurements; the appropriate information and conversion factors are provided in both English and metric units in the tables.)
1. Before starting the activity discuss the nitrogen cycle, nitrogen fixation, and the concept of mutualism.
2. Arrange teams of 3-4 students per team.
3. Have them weigh and record the weights of their empty bags.
4. Demonstrate how to enter the cover crop field and place the quadrat so that you can sample all of the above ground plant material from the space being sampled.
5. Have each team choose a sample site in the field, place their quadrats at their sample sites and use their hedge shears to cut and remove all of the above-ground plant matter.
6. Label the bag(s) with the name of the team taking the sample and the type of cover crop being sampled.
7. Have each team weigh their bags and record the weights on the student worksheet.
8. Use Table 1  to determine the appropriate cover crop conversion factor based on type of cover crop being sampled. Multiply the cover crop sample weight by the conversion factor to arrive at the total amount of nitrogen in the cover crop.
Discussion and Reflection
1. Select a common vegetable crop they would like to grow on the cover crop field in the next growing season (Table 3. of Student Worksheet).
2. From the table, identify the nitrogen needs of each selected vegetable crop.
3. Calculate how much nitrogen the cover crop could provide each selected crop as a percentage of that vegetable’s nitrogen needs (Table 4. of Student Worksheet).
Based on the above, encourage the students to consider the broad economic value of the cover crop providing biologically generated on-site fertilizer.

Student Worksheet
Estimate the nitrogen contribution of a cover crop by using the weight of your biomass sample. Answer questions A,B,C,D, and E.
A. What is the weight of your cover crop biomass sample? ________ lb or kg (circle one)
B. What is the conversion factor for your particular cover crop? _______ (see Table 1.)

Table 1. Cover Crop Conversion Factors from Wet Weight to Nitrogen Content
                   Cover Crop Conversion Factor (Metric kg/hectares)
Vetch: Lana (Wooly Pod) or Purple 28 59
Bell Bean 18 37
Berseem Clover 23 48
Blackeyed pea (Cowpea) 21 44
Grass (average) 11 23
Legumes (average) 23 40
C. What is the estimated total amount of nitrogen contributed by the cover crop to the soil
for the next season?
________________________ X __________________ = ______________________ kg/hectare
Cover Crop                                  Cover Crop                       Nitrogen Contribution
Sample Weight                            Conversion Factor                     by Cover Crop


If you were to plant your favorite vegetable in this field next season, what would it be?
__________________________________
D. What is that vegetable’s nitrogen need? _______ lbs/acre or kg/hectare (circle one)
(Select from table 2.)
Table 2. Typical Nitrogen (N), Needs of Vegetable Crops



Vegetable Crop  (kg/ha) 
 Artichoke  55-110                     Lettuce  135-200
Asparagus  90-165                     Muskmelon  110-165
Bean  65-135                              Onion 135-335
Broccoli  110-225                       Pepper, Chili 90-165
Brussel Sprouts  110-225            Pepper, Sweet  135-270
Cabbage 110-225                       Potato, Irish  165-335
Carrot  90-165                           Potato, Sweet  90-135
Cauliflower  110-225                  Spinach  90-165
Celery225-335                          Squash, Summer  90-165
Corn, Sweet 135-270                Tomato 110-225
Cucumber 90-165                     Tomato, Cherry  110-225
Garlic  110-225                         Watermelon  110-180

Source: FERTILIZER GUIDE FOR CALIFORNIA VEGETABLE CROPS
K. B. Tyler and 0. A. Lorenz, Department of Vegetable Crops, University of California, Davis, 1991
(Available at: http://vric.ucdavis.edu/veginfo/topics/fertilizer/fertguide.html)

E. What percentage of the vegetable crop’s nitrogen need from the soil was potentially
contributed by the cover crop? _________ %

_____________________ ÷ ____________________ X 100 = ____________________
Cover Crop                                  Vegetable’s                                  % Nitrogen Supplied
Nitrogen Contribution                      Nitrogen Need                           to Soil by Cover Crop

Nitrogen cycle.BBC-Bitesize

http://www.bbc.co.uk/schools/gcsebitesize/science/add_gateway_pre_2011/greenworld/recyclingrev2.shtml 

Nitrogen is essential for the formation of amino acids in proteins. The nitrogen cycle is a model that explains how nitrogen is recycled.
There's lot of nitrogen in air – about 78% of the air is nitrogen. Because nitrogen is so unreactive, it cannot be used directly by plants to make protein. Only nitrates are useful to plants, so we are dependent on other processes to convert nitrogen to nitrates in the soil.

1. Nitrogen gas is converted to nitrate compounds by nitrogen-fixing bacteria in soil or root nodules. Lightning also converts nitrogen gas to nitrate compounds. The Haber process converts nitrogen gas into ammonia used in fertilizers. Ammonia is converted to nitrates by nitrifying bacteria in the soil.
2. Plants absorb nitrates from the soil and use these to build up proteins. The plant may be eaten by an animal, and its biomass used to produce animal protein.
3. Urea and egested material is broken down by decomposers. This results in nitrogen being returned to the soil as ammonia.
4. Decomposers also break down the bodies of dead organisms resulting in nitrogen being returned to the soil as ammonia.
5. In some conditions denitrifying bacteria in the soil break down nitrates and return nitrogen to the air. This is usually in waterlogged soil. Improving drainage reduces this effect, making the soil more fertile.

Cover crops

http://www.motherearthnews.com/organic-gardening/cover-crops-improve-soil-zmaz09onzraw.aspx#axzz3KqFhHfgD

A cover crop is a crop planted primarily to manage soil erosion, soil fertility, soil quality, water, weeds, pests, diseases, biodiversity and wildlife in an agroecosystem (Lu et al. 2000), an ecological system managed and largely shaped by humans across a range of intensities to produce food, feed, or fiber. Currently, not many countries are known for using the cover crop method.
Cover crops are of interest in sustainable agriculture as many of them improve the sustainability of agroecosystem attributes and may also indirectly improve qualities of neighboring natural ecosystems. Farmers choose to grow and manage specific cover crop types based on their own needs and goals, influenced by the biological, environmental, social, cultural, and economic factors of the food system in which farmers operate (Snapp et al. 2005).

Legumes

Legume cover crops can fix nitrogen from the air, supplying nitrogen to the succeeding crop as well as protecting the soil from erosion and adding organic matter. The amount of nitrogen fixed varies between species, although generally, more top growth equals more nitrogen fixed. Some legume species have aggressive tap roots which can break up subsoil compaction, but this requires more than one year’s growth to happen.

How Cover Crops Help

Since the early 1900s, farmers have used cover crops to restore fertility to worn-out land. In addition to helping bulk up soil with organic matter, cover crops prevent erosion, suppress weeds, and create and cycle soilborne nutrients using the power of the sun.
Rhizodeposition is a special advantage to working with cover crops. Many plants actually release sugars and other substances through their roots. They are like little solar engines, pumping energy down into the soil. With vigorous cover crop plants, this process goes on much more deeply than you would ever dig — 6 feet for oats and rye! If you are leaving your garden beds bare in winter, you are missing the chance to use cold-hardy crops such as cereal rye or oats to solar-charge your soil. Thanks to this release of sugars, the root tips of many plants host colonies of helpful microorganisms, and as the roots move deeper, the microbes follow.
But so much for scientific talk. If you’ve experimented with cover crops, perhaps you have dug up young fava beans or alfalfa seedlings to marvel at the nitrogen nodules on their roots. Pull up a marvelous mop of fibrous roots and shake out the soil. What crumb! The soil’s structure is nothing short of amazing! These are the moments an organic gardener lives for.

Read more: http://www.motherearthnews.com/organic-gardening/cover-crops-improve-soil-zmaz09onzraw.aspx#ixzz3KqHNI1uO

Plate Tectonic animation

http://earthguide.ucsd.edu/eoc/teachers/t_tectonics/t_tectonics.html

Paleomagnetism

National Geographic Colliding Continents

Plate Tectonics

plate tectonics