Table 1: Mass of Nutrients per Bushel of Crop7 Crop


Wheat Corn Canola Soybeans


Removal In Straw Removal In Straw Removal In Straw Removal In Straw


Nitrogen (Urea) (kg)


1.480 0.600 0.960 0.550 1.900 1.240 3.800 1.270


Phosphorus (MAP)


(kg) 0.510


0.190 0.380 0.170 0.910 0.370 0.720 0.060


Potassium (KCl) (kg)


0.330 1.040 0.210 0.760 0.390 1.360 1.060 1.520


Procedure: 1. Hold up an empty bushel basket and ask students if they know what it is? Expect the obvious, “It’s a basket,” but probe a little deeper to see if any will recognize it as a “bushel basket!”


2. Explain that this basket represents one bushel of a crop. Note that originally the bushel was a unit of volume but has sub- sequently been changed to a mass bushel as commerce dictated a more precise measurement. Ask students what a good yield for the crops you are using would be? This may be 40-60 bushels per acre for canola or more than 140 bushels per acre for corn. These yields will vary considerably based on where you are living, so try to find out what realistic numbers are for your nearest farmland.


NOTE: The suggested crops are commonly grown where I live. Have students guess at the yields or do some quick research to


find the yields. In regions, where the crops listed are not common, modify the activity for other foods, such as fruits, vegetables or rice, each with different yields.


3. If doing this activity in conjunction with What is an Acre?, explain the area required to produce the number of bushels for the crop you are working with. For example, the one acre staked out would produce 40 to 60 baskets of canola. You may want to look up the current price for that crop to give students an idea of the value produced. If Canola is $10 per bushel for example, the area would generate $400 to $600 of value.


4. Next show the nutrients bottles. Begin with nitrogen and show the total amount needed (both bottles) to produce the crop. Then explain that one bottle represents the amount of nitrogen removed with the seeds (generally removed and taken to where it will be consumed or used). The second portion represents the nitrogen that is used by the plants but is left in the straw after harvesting. This nitrogen is not removed from the ecosystem but is available for use in the nitrogen cycle.


5. Repeat this process with the samples of phosphorus and potassium, and if available sulfur. 6. Reiterate to the students that these bottles represent the nutrients required to produce just one bushel basket and that this acre would require 40-60 times that for canola, and perhaps 140 times that for corn.


By this point the questions and comments will be abundant. “Do we have to add all that?” “Where does that come from?”


“Isn’t this bad for the environment?” “Can we use manure?” Can we use compost?” They are asking the questions which will allow you to teach them about the nutrient cycles with a focus on an agro-ecosystem.


7. This may be a good time to show them soybeans. As soybeans are legumes, they have nitrogen fixing bacteria housed in the nodules of their root systems. Soybeans are plants and they absolutely need nutrients to grow. The difference for legumes is that the nitrogen fixing bacteria living with them takes much of the nitrogen they need from the air and fix it into a form the plants can use. This reduces the need for an external nitrogen source such as nitrogen fertilizer. Thus, legumes can be a valuable part of the using crop rotation as a best management practise


NOTE: there are many varieties of legumes, soybeans is but one example. Plants need food too! And as this activity shows, plants require large amounts of nitrogen, phosphorus and potassium, the


so-called macro-nutrients. There are actually 17 essential nutrients8 but these three are used by plants in the greatest quanti- ties and have some of the most profound impacts on the pillars of sustainability – the environment, society and the economy. As most farms in North America are family farms, our farmers and the agriculture community strive to ensure the best management practises are utilized ensure the viability of the farm for generations to come.


Page 42 GREEN TEACHER 113


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