3: QL Inorganic and microbial fertilizers
Learning Objectives (Chapter 5)
Understand how different elements differentially contribute to the growth of an organism.
Analyzing correlations between samples
Background
In order for a plant to grow and thrive, it needs a number of different chemical elements. In Chapter 5 you
learned that carbon, hydrogen, and oxygen are required for the formation of carbohydrates, including
cellulose and starch found in most plants. Plants obtain carbon from CO 2 from the atmosphere and
hydrogen and oxygen from water and CO2 (youll learn more about this in Chapter 10). But plants also
need to synthesize proteins that require, in addition to carbon, hydrogen, and oxygen, large amounts of
nitrogen, and a phospholipid membrane which requires large amounts of phosphorus. Potassium is an
essential ion for many functions and makes up 1 -2 percent of the weight of a plant. Other chemicals are
needed in much lower quantities and are generally available in most soils. Therefore, plants cannot grow
without these and other additional elements (note: hydroponic growing requires mineral nutrients in
solution, not just water).
In most soils, the availability of nitrogen (N), phosphorus (P), and potassium (K) is a big limit to growth. To
make plants grow faster, these elements can be added to the soil in a form that plants can absorb . These
macronutrients are found in most commercial fertilizers.
Fertilizer is generally sold containing varying ratios of nitrogen (N), phosphorus (P), and pot assium (K),
listed as a series of numbers, such as 10-10-10 or 0-0-60, representing the ratio of N:P:K, respectively.
Each number is a percentage. For example, in a 50 lb bag of 10 -10-10 fertilizer there is 10% of each
nutrient. So the bag contains at total of 15 lb of nutrients (5 lbs each).
You want to grow tomatoes on your farm and want to experiment with different fertilizer combinations.
You set up 5 beds of tomatoes, four fertilized and one unfertilized control. You obtain the following at
the data end of the season:
Fertilizer
Plant height (m)
Root weight (kg)
Total Fruit (kg)
5-5-5
0.8
2.3
4.2
8-0-24
0.3
1.0
0.2
16-0-0
0.2
0.7
0.1
5-10-5
0.85
2.7
6.8
No Fertilizer
0.25
0.8
0.2
Homework
Instructions: On the answer form (download from Blackboard) write your answers in the
space provided. For each question write the answer in one complete sentence and
explain/support your answer with one or more supporting sentences. For numerical
answers use the supporting sentence(s) to explain how you arrived at your answer.
Round numerical answers to the nearest tenth. For graphing questions, use the Graph
Answers worksheet (see bottom tabs on answer form).
1. Plot the relationship between plant height and root weight and add a trendline. To
receive full credit, you must plot the data correctly as an X-Y scatter plot, correctly add
a trendline, label the x- and y- axes with the appropriate terms and units of measure,
and provide a meaningful title.
2. Describe the relationship between plant height and root weight.
3. Which element is absent or at very low amounts in the native soil?
4. What major macromolecules described in Chapter 5 would be hard to synthesize
without the element answered in Question 3?
5. In a 25 lb bag of 8-0-24 fertilizer, how many pounds of nitrogen, phosphorus, and
potassium are in the bag?
Quantitative Technique: Trendlines
A trendline is a line that expresses the average rate of change of a dependent variable (y-axis) in
response to changing independent variable (x -axis). Frequently called a regression line, a tre ndline can
be used for both interpolation and extrapolation if you know its mathematical function. For a straight or
linear trendline, the equation for the line is y=mx+b, where m
is the slope and b is the y-intercept.
To display a trendline using Excel, simply right-click a point on an X-Y chart and click on Add
Trendline. To display the equation go to Options in the pop-up window and select the button for
Display equation on chart.