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Laboratory Manual

Experiment 4. An Assessment of the Relative Values of Nitrogenous Fertilizers for the Growth of Spinach or Radish

Many green, leafy vegetables and root crops of high succulence (crisp, high moisture content) respond well to nitrogen fertilization. It is essential that these vegetables have a plentiful supply of nitrogen in order that they maintain their green color and succulence. Nitrogen deficiency in spinach and radish is shown by restricted shoot and root growth and by yellowing of the leaves. Nutritional value and palatability of spinach decreases with nitrogen deficiency.

Too much nitrogen applied to spinach and radishes is undesirable in that it may lead to excessive nitrate accumulation in the leaves and roots. Under luxury conditions of nitrogen nutrition more nitrate enters the plants than is needed for their nutrition; consequently, nitrate accumulates. Nitrate accumulation is not unique to spinach and radishes but may occur in other vegetables. Nitrates in vegetables may be a hazard to human health under certain circumstances. Therefore, the best source of nitrogen for a crop, such as spinach, would be a fertilizer which would maintain the bright green color of the leaves but which would not provide nitrogen in rates or amounts which would lead to nitrate accumulation in the fresh vegetable. Thanks to new varieties, higher yields and greater planting densities nitrate concentrations in vegetables are no higher today than they were eighty years ago, but, nevertheless, nitrate contents in vegetables and other food products are still a matter of deep concern to the grower and the consumer.

Experiment

You are provided with a greenhouse soil mix: John Innis Potting Compost, a synthetic compost which consists of: 7 parts soil (by volume):3 parts peat moss:2 parts sand with 120 g bonemeal (20% P2O5)and 120 g ground limestone per bushel of mix

This mix does not provide enough nitrogen to grow a crop without nitrogen deficiency symptoms. It is necessary to add between 200 and 400 mg available nitrogen per 1000 g pot of mix in order to obtain optimum growth of spinach or radishes.

You are provided with several sources of nitrogen. Calculate the amounts of these fertilizer materials needed to provide 100, 200 400, and 800 mg N per pot (1,200 g of soil) and record these values in the table on page 2.

Fertilizers to be added as sources of nitrogen:

Fertilizer

Percent N

1. Bloodmeal (BLO)

12

2. Alfalfa meal (ALF)

2.5

3. Cottonseed meal (CSM)

6

4. Activated sewage sludge (SEW)

5

5. Dried cow manure (COW)

2

6. Compost (COM)

1

7. Feather meal (FM)

15

8. Ammonium nitrate (AN)

34

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-----------------------------Amount of nitrogen fertilizer to apply, g/pot ---------------------------------

Amount of N to apply, mg/pot

BLO

ALF

CSM

SEW

COW

COM

FM

AN

100

_________

_________

_________

_________

_________

_________

_________

_________

200

_________

_________

_________

_________

_________

_________

_________

_________

400

_________

_________

_________

_________

_________

_________

_________

_________

800

_________

_________

_________

_________

_________

_________

_________

_________

l. Prepare one pot of the artificial compost with no fertilizer nitrogen added. Prepare labels using a wooden or plastic pot label marked "0" in pencil or permanent ink.

2. Prepare one pot with each nitrogen fertilizer added at the quantities shown above. First fill the pot with synthetic compost, firming the mix by hand, to within 1" of the top. Dump mixture on bench, and mix in fertilizer. Prepare a label for each treatment indicating the amount and kind of fertilizers and your laboratory section.

3. Plant twenty spinach or radish seeds in each pot. Cover about 1/4 to 1/2 inch.

Record date _______________________. Record cultivar _____________________________.

4. Wet the soil. (In the greenhouse, add about 200 ml of water to each pot; push seeds that may have floated from the soil back into the soil.)

In about 55 days the spinach will be ready to harvest. The radishes will mature in about 38 days. Meanwhile make notes of germination, growth, and development of nitrogen deficiencies for each fertilizer material at each quantity of application.

GERMINATION - Count number of seedlings per pot at one or two weeks after seeding. Results 1999

________________________________________________________________________________ _____

--------------------------------Number of seedlings emerging per pot-- ---------------------------------

Amount of N to apply, mg/pot

BLO

ALF

CSM

SEW

COW

COM

FM

AN

100

_________

_________

_________

_________

_________

_________

_________

_________

200

_________

_________

_________

_________

_________

_________

_________

_________

400

_________

_________

_________

_________

_________

_________

_________

_________

800

_________

_________

_________

_________

_________

_________

_________

_________

After germination counts are taken, thin gradually over two weeks to five plants per pot. Reseed pots in which count is less than five plants.

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NITROGEN DEFICIENCY OR OTHER SYMPTOMS. Rate symptoms by visual indexing.* Results 1999

-------------------------------Visual index of nitrogen deficiency symptoms------------------------------

Amount of N to apply, mg/pot

BLO

ALF

CSM

SEW

COW

COM

FM

AN

100

_________

_________

_________

_________

_________

_________

_________

_________

200

_________

_________

_________

_________

_________

_________

_________

_________

400

_________

_________

_________

_________

_________

_________

_________

_________

800

_________

_________

_________

_________

_________

_________

_________

_________

*Use 0 for no deficiency and 1, 2, and 3 for slight, moderate, and severe deficiency symptoms. Use negative numbers to designate severity of toxicity symptoms, if any.

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GROWTH (Make general comments on growth. At harvest record fresh weights)

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Plants will be harvested during a laboratory period. When plants are harvested they will be weighed, dried, and ground, and analyzed for nitrates. You will be given results from each laboratory section so that you have replications of treatments.

FRESH WEIGHTS Results 1999

______________________________________________________________________________________________

-------------------------------Weights of radish roots & shoots, g/pot-- ---------------------------------

Amount of N to apply, mg/pot

BLO

ALF

CSM

SEW

COW

COM

FM

AN

100

_________

_________

_________

_________

_________

_________

_________

_________

200

_________

_________

_________

_________

_________

_________

_________

_________

400

_________

_________

_________

_________

_________

_________

_________

_________

800

_________

_________

_________

_________

_________

_________

_________

_________

______________________________________________________________________________________________

Answer these questions:

1. Which of these treatments gave the largest plants? _______________________________________________________

______________________________________________________________________________________________

2. Which of these treatments gave the greenest color to the plants? ____________________________________________

______________________________________________________________________________________________

3.What were the factors that were responsible for poor seed germination with some of the fertilizers?

______________________________________________________________________________________________

4. How would you avoid the adverse effects which these fertilizers have on seed germination?

______________________________________________________________________________________________

5. Explain why some of the fertilizers that initially inhibited germination supported better growth of plants than the fertilizers that did not inhibit germination.

______________________________________________________________________________________________

6. What deficiencies, toxicities, or other abnormalities did you note on these plants aside from the effects on germination and nitrogen deficiency. Describe the conditions under which they were noted.

______________________________________________________________________________________________

7.What was the effects of the fertilizers on nitrate contents in these plants? Nitrates in roots.

______________________________________________________________________________________________

8. Write a short paragraph in which you evaluate these fertilizers as nitrogen sources.

______________________________________________________________________________________________

Produced and maintained by Allen Barker
University of Massachusetts, Amherst.

Fertilizer	Percent N
1. Bloodmeal (BLO)	12
2. Alfalfa meal (ALF)	2.5
3. Cottonseed meal (CSM)	6
4. Activated sewage sludge (SEW)	5
5. Dried cow manure (COW)	2
6. Compost (COM)	1
7. Feather meal (FM)	15
8. Ammonium nitrate (AN)	34

Amount of N to apply, mg/pot	BLO	ALF	CSM	SEW	COW	COM	FM	AN
100	_________	_________	_________	_________	_________	_________	_________	_________
200	_________	_________	_________	_________	_________	_________	_________	_________
400	_________	_________	_________	_________	_________	_________	_________	_________
800	_________	_________	_________	_________	_________	_________	_________	_________