Unit 13 - Soil Fertility & Fertilizers

Chapter 2 - Fertilizer Problems

Fertilizer problems are not hard if we remember this formula:
Pounds of Fertilizer Needed (PFN)=PNN ÷ PNIF
and (PNN=Pounds of nutrient needed) and (PNIF=Percentage of nutrient in fertilizer)

Question : How much ammonium nitrate(PFN) do you need in order to apply 4 lbs.of nitrogen(PNN) per 1000 ft²? note: most lawn applications are measured in area of 1000 ft² and agricultural fields are measured in acres or hectares.
From Table 1 or the Table in the Lab Manual in Investigation 1, we find that ammonium nitrate is 34% N (PNIF), and, using the formula, (PFN=PNN(4) ÷ PNIF(0.34)=11.8 lbs.

Sample Fertilizer Problems:

1.Question: If 4 lbs of nitrogen are required per 1000 ft², how many pounds of ammonium nitrate are required? (see Table 1
Answer: Fertilizer needed=4/.34=11.8 lbs of NH4NO3

2. Question: What is the quantity of N in 2 tons of urea? Urea=Table 1
Answer: 2 tons=4000 lbs x .45=1800 lbs of N

3. Question: Which is cheaper per pound of nitrogen? 20 lbs of 33-0-0 for $7.95 or 50 lbs of 6-30-0 at $3.95
Answer: 20 x .33=6.6 lbs N; $7.95/6.6. lbs=$1.20/lb Nand 50 x .06=3 lbs N; $3.95 /3lbs=$1.31/lb N

Sample fertilizer problems using commercial fertilizer products.

1. Using Scotts Fertilizer ($21.59 for a 28.58 lb bag), if the nitrogen recommendation was 4 lbs per year per 1000 square feet:
a) What is the amount of yearly nitrogen needed for a yard that is 150 ft by 130 ft?=______
b) How much P2O5 is being applied per 1000 ft2?=__________
c) How much elementalK per 1000 ft2is being applied?=____________
d) What is the total cost? (sale price)=_______________
e) What is the cost per pound of nitrogen for the nitrogen actually applied to the soil?=________
f) If ammonium nitrate was available at $4.75/50 lbs, would it be cheaper?=___________

2. Pure Blend Hydro Organic Tea Solution (0.4-0.1-0.5). The Blend weighs 9 lbs /gallon (note 4 qts/ gallon)
a) What is the quantity of N in one container (32 oz) of this fertilizer?=_______
b) What is the cost of nitrogen per pound.=_________
c) How does this compare to the turf fertilizer in question 1.=_____________

3. Using the table for established alfalfa for the following questions about using Howe's Best Bet K fertilizer.( 0-0-60)

Potash Recommendations for Established Alfalfa
Yield Goal ton/acre K Soil Test  in PPM    
  0-40 41-80 81-120 121-160 161 +
<3 145 100 55 10 0
5 240 165 90 15 0
>7 380 265 145 20 0
how fert

a) Determine the potassium recommendation for a 5-ton yield where the potassium soil test was 78 ppm or 0.2 m.e. per 100 grams. (1 m.e. of K=.039 g).=______
b) Using the "Howe Best Bet" fertilizer, what is the amount of fertilizer needed per acre?=______
c) At $3.99/ 66.67 lb. bag what is the cost/acre?=_________

Fish Fert4. Alaska Fish Fertilizer compared to Bat Guano. Bat Guano

a) Compare the price per pound of nitrogen for each material.=_____________
b) Which would you use on your garden? ____________________ Explain why__________________________________

Natural Fertilizer Products

Some interesting information on guano and fish fertilizer.
The word guano originated from the Quichua language of the Inca civilization and means "the droppings of sea birds". It is a misnomer to refer to bat dung as guano. As the word is used today, guano describes both bat and sea bird manure. The most famous guano was that used by the Inca. The guano would collect on the rainless islands and coast of Peru. Atmospheric conditions insured a minimal loss of nutrients. There is very little leaching nor is there a considerable loss of nitrogenous matter. The Inca would guard and regulate the treasured soil enricher. Access to the guano deposits were restricted to chosen caretakers. Disrupting the rookeries could result in punishment by death.

Guano became a very important part of the development of agriculture in the United States. During the peak of the guano era, drastic steps were taken to maintain a supply for the U.S. farmer. On August 18, 1856, Congress passed an act to "authorize protection to be given to citizens of the United States who may discover guano, under which any citizen of the United States was authorized to take possession of and occupy any unclaimed island, rock or key containing guano". The discoverers of such islands were entitled to exclusive rights to the deposits thereon, but the guano could only be removed for the use of the citizens of the United States. (from Home Harvest Garden Supply Online)

"Fish emulsion comes from a number of sources, but a sizable majority (and 100% of Alaska Fish Fertilizer) comes from one of two sources- the fish meal trade or the fish canning industry. But as catching and canning of all fish moves off of US lands, and into Asian countries and onto shipboard canneries, more and more of the fish emulsion comes from the domestic fishmeal industry.

In the Atlantic Ocean and the Caribbean, there is a small, 8 inch long fish called the menhaden. The menhaden has no edible value (it is oily, bony, and has very little edible meat) for humans. The menhaden, Brevoortia tyrranus, is a medium-sized, filter-feeding, schooling fish that is closely related to herring, sardines, and shad. Menhaden spawn in the ocean but migrate into estuarine waters to feed on the algae that fix the sun's energy via photosynthesis. Menhaden are in turn eaten by a large variety of secondary consumers like bluefish, mackerel, striped bass, and sharks. Their sheer abundance in estuaries and along coasts makes menhaden extremely important to the marine food web, for harvesting nutrients washed from the land into the ocean that are in the algae, and to local fishermen. Their catch represents 40% of the US commercial finfish fisheries. Menhaden Fish Link to menhaden fish problems

These fish are caught exclusively for their protein values. Once caught and brought back to shore, they are dumped onto a long conveyer belt, which takes the fish through an oven, where the fish is cooked at 210 degrees F. Then the fish go into a screw press, where the liquids and oils are pressed out. The solids go on to be processed into fish meal, animal feed, and other industrial products. The liquid is more valuable than petroleum, with pure fish oil selling for more than twice the price of crude oil.

The liquid, called stickwater, is placed in a centrifuge, where the oil is skimmed off, and the heavier components, the fish solubles, are boiled down to a thicker, gummier solution that is sold as fish emulsion. A small amount- less than 0.1% by weight- of phosphoric acid is added to drop the pH of the solubles to 4.5 or below. Without this phosphoric acid, the enzymes in the fish would cause it to decay, create gases, and begin to smell horrid- and, all the states realize this, and within certain guidelines, it is still considered 100% Natural Organic. It is then sold on the open commodities market to animal food companies, which use it as flavoring for dog and cat food, additional protein for animal crops (such as cattle), etc. and to companies like Alaska Fish Fertilizer. Thus the fish in Alaska Fish Fertilizer do no come from Alaska. ( from Bill Ginn Marketing Coordinator Alaska Fish Fertilizer)

1. a) 150 ft. x 130 ft.=19,500 ft2
19,500 ft2 x 4 lbs/1000 ft2=78 lbs of nitrogen
Scotts fertilizer grade=28-3-3 and 78 lbs N /.28=278.6 lbs of fertilizer
each bag was 28.58 lbs; 278.6 lbs /28.58=9.74, or 10 bags needed

b) 278.6 lbs of 28-3-3 or 278.6 x .03=8.3 lbs P2O5 applied 8.3/19.5=.42 lbs/1000 ft2

c) 278.6 lbs fertilizer added x .03(% K20)=8.34 lbs K2O & 8.34 /19.5( there is 19,500 ft2 in the yard)=.43 lbs K2O & 0 .43lbs K2O x .83 (% K in K2O=.35 lbs K /1000 ft2

d) 10 bags x $21.59/bag=$215.90

e) Price per pound; $21.59(price per bag)/(28.58 lbs. x 0.28(N in 1 bag) )=$2.69/lb of N

f) Ammonium nitrate=34-0-0 & $4.75 (price per bag) /.(34 x 50( N in a bag) )=$0.28/lb of N=yes ammonium is cheaper

2. a) N in 32 oz, 1/4 gallon=9 ÷ 4=2.25 lbs & 2.25 x .004(% N in fertilizer)=.009 lbs N in one container
b) Price of container=$ 9.95 ÷ .009 ( N in Container)=$1,105.56 per pound of N
c) Only a difference of $1102.87.

3. a) 0.2 m.e./100 grams x .039 g/m.e. (for K)=.0078 g/100 grams
& set up a ratio of .0078 g /100g as x lbs/1,000,000 or X=78 ppm of K in the soil/acre.
From Table above: in the 41-80 (ppm K per acre) column for 5 ton yield, 165 lbs K2O/acre are needed
b) using 0-0-60 "Howe best Bet" 165 lbs per acre ÷ 0.6 (% K2O in fertilizer)=275 lbs of fertilizer and each bag is 66.6lbs or 275 ÷ 66.7=4.13 bags/acre
c) @3.99/bagx 4.13 bags=$16.45/acre

4.a) Bat Guano 10 lbs x .08=0.8 lbs N at $ 39.95 or 39.95 ÷ 0.8=$49.94 per lb of N.
& Fish 16 oz is 0.125 of a gallon or=9 lbs./gal x 0.125=1.125 lbs & 1.125 x .05 (% N )=.056 lbs of N that costs $4.50 or $4.5 ÷ 0.56lbs=$ 80.35 / lb N
c) Bats, because they eat bugs and make cheaper N and you don't have to harvest them and disrupt the ecology of the ocean to get the nutrients.

flying bat

Chapter 3 Nitrogen Fertilizers

Fertilizer Chapters

Lab Units

© Terence H. Cooper & Regents of the University of Minnesota, 2009 The University of Minnesota is an equal opportunity educator and employer.