Texas Cooperative Extension,
Texas A&M University, College Station, Texas

July-August, 2007


How Much Fertilizer Shall I Use? - from USDA Leaflet No. 307. (A Gardener's Guide for Converting Tons or Pounds Per Acre into Pints, Cups, Tablespoons, or Teaspoons per Row or Plant)

      How to calculate small measures of fertilizers from recommended applications by weight for large areas      

Books and bulletins on agriculture and gardening usually give recommendations for the use of fertilizers and lime in tons or pounds per acre, or in pounds per thousand or hundred square feet. The gardener often finds difficulty in converting these weights into the measures needed for a small plot or for a single row or a single plant; and frequently he has no scales for weighing. This folder makes the conversions for him, using the common household measurements of pints, cups, tablespoons, and teaspoons.

For example, if 300 pounds of superphosphate or mixed fertilizer are recommended per acre, you will find by turning to table 1 that this means 7 pounds per thousand square feet, or 11 ounces (1 1/2 cups) per hundred square feet. Then, turning to table 2, you will find that 1 1/2 cups per hundred square feet means 1/2 cup for each 10-foot row if the rows are 3 feet apart, or 6 tablespoonfuls for each plant if the plants are spaced 5 x 5 feet. A large number of such conversions are given for various kinds of fertilizer material and to fit various needs.

Table 3 shows volume measures (in cups, tablespoons, etc.) of chemicals to be added to each bushel of plant material in making a compost pile, based on directions in weight per ton of plant material.

The rates to be selected for the various materials depend on the soil and its previous treatments and the requirements of the plants. Certain materials- ground limestone, where needed, and superphosphate- are used in relatively large quantity; borax and others, sparingly. For example, small-rate supplemental additions of ammonium nitrate can be given tomatoes with advantage, whereas very much would injure the plants.

The values tabulated are near enough for all practical purposes, though they are only approximate, since the weight of a given volume of a material will vary with its moisture content and texture. In making the calculations it was assumed that the materials will be scooped up into the container without any packing, and that they will be loose and not lumpy. The standard pint, cup, tablespoon (tbs.), and teaspoon (tsp.) are used for liquid measure. Other than for liquids, level-full measures are understood, with two exceptions: Slightly heaped (indicated by h); and a trifle less than full (by s).

For materials not included in the lists, one may weigh carefully a full pint and determine approximately the group to which it belongs.

It will be useful to remember (1) that a pint of water weighs just a little more than a pound (actually, 1.046 pounds); (2) that an acre is equivalent to 43,560 square feet (a plot about 209 feet square); and (3) that a pint is equivalent to 2 cups, or 32 tablespoons, or 96 teaspoons.       Table 1. Weights of various fertilizing materials per acre, per 1,000 square feet, and per 100 square feet and the approximate equivalent-volume measures for 100 square feet, grouped according to weight in comparison with that of water.  

Materials
Weights Specified per --

Volume Measure for 100 Sq. Ft.

Acre

1,000 Sq. Ft.

100 Sq. Ft.
  Pounds Pounds Pounds Pints
Weight about the same as that of water
Examples: Cal-Nitro (or A-N-L), manure salts.
1,300 30 3 3
870 20 2 2
435 10 1 1
      Cups
220 5 1/2 1
110 2 1/2 1/4 1/2
         
        Pints
Weight about 1 3/10 that of water
Examples: Ground limestone, ground dolomitic limestone, granular sodium nitrate, potassium sulfate.
5,660 130 13 10
3,485 80 8 6
870 20 2 1 1/2
    Ounces  
565 13 21 1
      Cup
280 6 1/2 11 1
         
      Pounds Pints
Weight about 9/10 that of water
Examples: Ammonium phosphate, double superphosphae, superphosphate, mixed fertilizers (5-10-5, 10-6-4, etc.), muriate of potash.
1,960 45 4 1/2 5
1,650 38 3 3/4 4
1,220 28 2 3/4 3
1,000 23 2 1/4 2 1/2
    Ounces  
785 18 30 2
610 14 21 1 1/2
390 9 15 1
      Cups
300 7 11 1 1/2
200 4 3/4 7 1/2 3
100 2 1/4 3 1/2 1/2
  Ounces   Tbs.
50 18 2 4
11 5 1/2 1
         
Weight about 8/10 that of water
Examples: Epsom saolts, bonemeal.
Pounds Pounds Pounds Pints
1,740 40 4 5
650 15 1 1/2 2
    Ounces Cups
175 4 6 1/2 1
      Tbs.
44 1 1 1/2 4
         
      Pounds Pints
Weight about 7/10 that of water
Examples: Activated sewage sludge, urea, ammonium sulfate, granular ammonium nitrate, aluminum sulfate, granular borax.
1,740 40 4 6
1,525 35 3 1/2 5
650 15 1 1/2 2
    Ounces  
300 7 11 1
      Cup
150 3 1/2 5 1/2 1
      Tbs.
44 1 1 1/2 4
  Ounces    
11 5 1/2 1
         
    Pounds Pounds Pints
Weight about 6/10 that of water
Examples: Cottonseed meal, sulfur, fish scrap.
1,300 30 3 5
545 12 1/2 1 1/4 2
    Ounces  
260 6 10 1
      Cup
130 3 5 1
         
      Pounds Pints
Weight about 5/10 that of water
Example: Hydrated lime.
1,100 25 2 1/2 5
435 10 1 2
    Ounces  
220 5 8 1
    Cup
110 2 1/2 4 1
         
Manure (moist): Tons   Pounds Bushels
Loose 13 600 60 2
Packed 13 600 60 1
Dry straw or leaves packed tightly with hands 5 250 25 2
         
    Table 2. Approximate equivalent-volume measures of materials to use in the row and per plant at various rates per 100 square feet.  

Rates per 100 Square Feet Rates per 10 feet, Rows Spaces -- Rates per Plant, Spaced --
3 ft. 2 ft. 1 ft. 5 x 5 ft. 2 1/4 x 2 1/4 ft. 2 x 1 ½ ft.
Pints Pints Pints Pints Pints Cups Cups
10 3 2 1 2 1/2 1 1/2
  Cups Cups Cups Cups    
6 3 1/2 2 1/2 1 1/4 3 (h) 1/2 (h) 1/4
5 3 2 1 2 1/2 1/2 1/4
          Tbs. Tbs.
4 2 1/2 1 1/2 3/4 2 6 1/2 (h) 3
3 1 3/4 1 1/4 (h) 1/2 1 1/2 5 2 1/2
2 1/2 1 1/2 1 1/2 1 1/4 4 2
      Tbs.      
2 1 1/4 3/4 6 1/2 1 3 1/4 1 1/2
1 1/2 (h) 3/4 (h) 1/2 5 3/4 2 1/2 (h) 1
Tbs.       Tsp.
1 1/2 6 3 1/4 1/2 1 1/2 2 1/2
Cups       Tbs.    
1 1/2 1/2 5 2 1/2 6 1 1 1/2
  Tbs.       Tsp.  
1 5 3 1/4 1 1/2 4 2 1/2 3/4
1/2 2 1/2 1 1/2 3/4 2 1 1/4 1/2
Tbs.   Tsp. Tsp.      
4 1 1/4 2 1/2 1 1/4 1 1/2 1/4
  Tsp.          
1 1 (h) 1/2 1/3 1/4 1/6 1/12
Bushels Bushels Pecks Quarts Bushel Quarts Quarts
2 (h) 1/2 1 1/2 6 1/2 3 1 1/2
  Peck     Peck    
1 (h) 1 (s) 1 3 1 1 1/2 3/4
             
h=Slightly heaped. s=A trifle less than full.    
             
Measuring Chemicals for Compost Heaps      

In making compost heaps with oak leaves as the chief source of organic matter, together with some grass and other plant materials, chemical aids are needed to disintegrate the more durable parts. If, however, a considerable quantity of lawn clippings and other plant tissue is used, the weight or measure of the chemicals named in table 3 may be somewhat reduced. When manure constitutes half the organic matter, no nitrogen is required-only the phosphate and limestone are needed. No limestone should be used if materials are to be applied to blueberries, azaleas, or similar acid-loving plants.

The compost may be prepared in layers, a layer of garden soil or dark-colored surface soil out of the woods about ½ to 2 inches thick, alternating with each 6- or 12-inch layer of fresh organic matter. When finished, the whole should be covered with 2 to 4 inches of soil.       Table 3. Volume measures of chemicals to be added separately to each bushel of plant material in making a compost pile, at specified rates per ton of material.  

Chemicals Weight Needed per Ton of Material Volume Measure Needed per Bushel of Material 1
Pounds Cups
Method 1:
(a) Either ammonium sulfate 80 1
or ammonium nitrate 50 1/2
(b) Either ground dolomitic limestone 2 60 2/3
or wood ashes 2 80 1 1/2
(c) Superphosphate 50 1/2
Tbs.
(d) Magnesium sulfate (Epsom salts) 3 8 1
Method 2: Cups
(a) Mixed fertilizer 5-10-5 300 3
(b) Ground dolomitic limestone 2 60 2/3
 
1 Packed tightly with the hands.
2 For acid compost omit lime, limestone, and wood ashes.
3 Epsom salts to be added only if dolomitic limestone is unavailable and ordinary limestone is used (at same rate).
   

Issued by Washington State University Cooperative Extension, and the U.S. Department of Agriculture. Reprinted from USDA Leaflet No. 307. Published May 1982.