Module #3
Greenhouse Operations and Management.
Nutrient Management and Plant Disease
Due Date: Thursday March 20th; (at the beginning of class)
Directions: You must show all work to receive credit. Late assignments
will not be accepted. The total assignment is worth 70 pts.
1. One of the most common tasks conducted by greenhouse growers is the preparation of
fertilizer solutions. This is an important task and the rate of nutrients applied can be very
critical to proper plant growth and development. Your textbook gives a couple of ways
to calculate ppm and a third way was reviewed Thursday February 28th. Calculate each
of the following answers.
a. Using the Rule of 75, calculate the amount of 33-0-0 fertilizer necessary to
produce a 225 ppm nitrogen solution. The answer should be presented as oz. of
fertilizer in 100 gallons of water
b. Use Table 9-7 (pg. 320) to recalculate the answer for (a). You will need to
interpolate.
c. Use the other common method for calculating ppm (the method reviewed at the
on 02/28/08) recalculate the answer for (a).
d. The greenhouse you work for has a fertilizer proportioner to simplify the
fertilization process. Using the first value calculated for (a) determine how much
fertilizer will have to be added to make 15 gallons of concentrate if the
proportioner is set to 1:25.
e. Your boss tells you that he really wants to reduce labor costs and would like his
custom fertilization blend to be applied through a proportioner set for a 1:400
dilution. This way only 2 gallons will have to be mixed up once a day. This
concerns you. Why?
f. Potential benefits of automatic proportioners used in conjunction with an
irrigation system, as compared to individual plant fertilization by hand, include
reduction in labor costs and lower volumes for fertilizer stocks. What is a
potential drawback of using proportioners?
g. Calculate the amount of 17-6-27 fertilizer necessary to make a small 15 gallon
batch of fertilizer to be applied by hand in the greenhouse. The final concentration
of N should be 125 ppm. Give answer in oz. of fertilizer/gallon of water.
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2. You are a new greenhouse manager at Super-Plant-World. They want to become the
Wal-Mart of the greenhouse industry. In order to facilitate large-scale production the
owners have invested heavily in an automatic fertigation system, which includes a
proportioner. This system is connected to the rest of the automatic trickle irrigation
system. Your immediate supervisor is responsible for calculating the fertilizer mixes that
go into the source tanks for the proportioner. Your current crop is poinsettias and you
have been noticing what you believe to be is nitrogen deficiency. You think that your
supervisor must have made a mistake because you requested that the final N
concentration of the fertilizer solution reaching your plants should be 200 ppm (plenty for
your poinsettias). Your supervisor won’t let you see the original fertilizer calculations.
Remembering what you learned in Greenhouse Operations and Management, you take a
conductivity meter and determine that EC for the nutrient solution coming out of a drip
emitter (in the poinsettia house you manage) is 0.32 mmho/cm. You do some checking
and you know that your supervisor is using a 20-10-20 fertilizer. You now know your
supervisor is clueless. How do you know? What is the approximate rate of N (ppm)
being supplied to your poinsettias based on the electrical conductivity (EC) of the
fertilizer solution? You confront your supervisor and it turns out that his nephew (clear
case of nephewtism) has been hired to manage the proportioner. His nephew’s job is to
see that the ratio is set to 1:25. Assuming your supervisor did his math right and the
fertilizer analysis is correct you are willing to bet your next two weeks salary that you
know what the proportioner has been incorrectly set at by the nephew. What is the
current incorrect proportioner setting?
3. You are working as an extension specialist for a major land grant university in the
Midwest. A grower calls in and describes the following problem to you. He has a crop
of geranium plants that has problems near the top of the plant. There is no general
chlorosis present in fully developed leaves or mature stems. However, the newest leaves
are thick, leathery and chlorotic. The new leaves are also crinkled and there are some
black sunken necrotic spots on the stem below the nodes. After discussing the matter for
a few more minutes you believe the grower has a nutrient problem. Using your text
determine which nutrient may deficient. How might the grower determine quantitatively
if your hypothesis was correct? Assuming you have made the correct diagnosis, what are
two compounds the grower might apply to begin to correct the problem and avoid the
deficiency in future crops?
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