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Publication #HS1200

How to Convert Liquid Fertilizer into Dry Fertilizer in Fertigation for Commercial Vegetable and Fruit Crop Production1

Guodong Liu, David Sui, and Gary K. England2

Introduction

Dry and liquid fertilizers are widely used in crop production. In recent years, more and more liquid fertilizers have been used in vegetable and fruit production. Typically, UF/IFAS recommendations are expressed as pounds per acre or kilograms per hectare. Thus, conversion either from a dry fertilizer basis (the UF/IFAS recommendation) to a liquid fertilizer basis, or from a liquid fertilizer source to the UF/IFAS recommended nutrient rate is often required for correct application rate. Thus, the purpose of this publication is to help growers understand the conversion method from liquid to dry fertilizer.

Why can this conversion be tricky?

Dry fertilizer and its active ingredients are both gravimetric—in other words, expressed as a weight per area. For this type of fertilizer, the calculations are fairly straightforward. For example, 100 pounds of a 10-10-10 fertilizer-grade material contains 10 pounds each of active ingredients nitrogen (N), phosphorus (P2O5), and potassium (K2O), equaling 30 pounds total of active ingredients, while the remaining 70 pounds consist of inactive materials. Figures 1 through 4 provide examples of fertilizer bags or bottles for either dry or liquid fertilizers.

Figure 1. 

A 10-10-10 dry fertilizer bag label. This 50-pound fertilizer has 5 pounds each of nitrogen (N), phosphorus (P2O5), and potassium (K2O) active ingredients. Namely, it has 15 pounds of active ingredients and 35 pounds of inactive ingredients.


Credit:

Guodong Liu


[Click thumbnail to enlarge.]

Figure 2. 

A 32-10-10 dry fertilizer bag label. This 50-pound fertilizer has 16 pounds of nitrogen (N) and 5 pounds each of phosphorus (P2O5) and potassium (K2O) active ingredients. Namely, it has 26 pounds of active ingredients and 24 pounds of inactive ingredients.


Credit:

Guodong Liu


[Click thumbnail to enlarge.]

Figure 3. 

A 3-3-3 liquid fertilizer label. This 1 quart of liquid fertilizer has 0.08 pounds (36 grams) each of nitrogen (N), phosphorus (P2O5), and potassium (K2O) active ingredients. Namely, it has 0.24 pounds (108 grams) of active ingredients and 2.4 pounds (1092 grams) of water or other inactive ingredients.


Credit:

Guodong Liu


[Click thumbnail to enlarge.]

Figure 4. 

A 4-3-3 liquid fertilizer label. This 1 quart of liquid fertilizer has 0.09 pounds (41 grams) of nitrogen (N) and 0.07 pounds (31 grams) each of phosphorus (P2O5) and potassium (K2O). Namely, it has 0.23 pounds (103 grams) of active ingredients and 2.02 pounds (917 grams) of water or other inactive ingredients.


Credit:

Guodong Liu


[Click thumbnail to enlarge.]

Liquid fertilizer active ingredients are expressed on a volumetric basis. The density of the liquid fertilizer is a key detail because it is impossible to know the weight of a liquid fertilizer before the density is known. Typically, the net volume and net weight are available on the liquid fertilizer label (Figure 3). The liquid density can be calculated based on these values. For example, on the Dr. Earth® label (Figure 3), its net volume is 0.946 liters (1 U.S. quart), and its net weight is 1.2 kilograms (2.64 pounds). Therefore, its density is 1.26 kilograms per liter or 10.51 pounds per gallon (2.64 pounds/U.S. quart x 1 gallon/4 quarts/gallon). This source is a 3-3-3 liquid fertilizer. A quart of this liquid fertilizer contains 0.08 pounds (36 grams) each of N, P2O5, and K2O (0.24 pounds or 108 grams of N, P2O5, and K2O in total) and 2.4 pounds (1089 grams) of water or other inactive ingredients.

Liquid fertilizers differ in density. They are related in terms of active ingredients, but the density is NOT always proportional to the total active ingredients. For example, Dr. Earth®has a lower percentage of active ingredients but greater density than AgGrand®. Dr. Earth® has 9% active ingredients in total (3% each for N, P2O5, and K2O), and its density is 10.51 pounds per gallon (Figure 3). Its total active ingredients per quart are 0.24 pounds. AgGrand® (Figure 4) has a greater percentage (4% + 3% + 3% = 10%) of active ingredients in total but lower density (9.01 pounds per gallon) than Dr. Earth® (10.51 pounds per gallon). Therefore, the former has more active ingredients (0.24 pounds) than the latter (0.23 pounds). This indicates the importance of the density of liquid fertilizers in actual active ingredients. The most common error in conversion from liquid fertilizer to dry fertilizer is neglecting the density. In the above example, if the density of the fertilizers is neglected, crop plants treated with AgGrand® fertilizer may actually be getting less nutrient each of N, P, and K than those treated with Dr. Earth® as the N, P, K source.

How does one convert liquid fertilizer to dry fertilizer?

To determine how many gallons of a particular liquid fertilizer are needed per acre, use the following equation (Burt, O'Connor, and Ruehr 1995):

For example, the IFAS recommendation for commercial tomato production in Florida is 200 pounds of N per acre. The injection rate would be 1.5–2.5 pounds per acre per day from 1 through 13 weeks after planting (Olson et al. 2012). For this example, assume 2 pounds per acre per day for a particular fertigation event and 10 acres to fertigate. Then, we need to use 20 pounds of N for the fertigation event. How many gallons of either of the above liquid fertilizers (Dr. Earth® or AgGrand®) are needed to supply 20 pounds of N to 10 acres?

(1) The 3-3-3 (Dr. Earth®) liquid fertilizer (fertilizer density: 10.51 pounds per gallon):

(2) The 4-3-3 (AgGrand®) liquid fertilizer (fertilizer density: 9.01 pounds per gallon):

AgGrand® has a greater N percentage than Dr. Earth®, so fewer gallons are needed to meet the 20 pounds of N requirement. Table 1 shows the calculation details for different acreage.

How many gallons of either of the above liquid fertilizers are needed to supply 20 pounds of P2O5 per 10 acres of tomato?

(1) The 3-3-3 (Dr. Earth®) liquid fertilizer (fertilizer density: 10.51 pounds per gallon):

(2) The 4-3-3 (AgGrand®) liquid fertilizer (fertilizer density: 9.01 pounds per gallon):

Both Dr. Earth® and AgGrand® have the same percentage of P2O5, but the former's liquid source has greater density, so fewer gallons are needed to supply 20 pounds P2O5 per 10 acres. Table 2 shows the calculation details for different scales of fertigation events.

For conversion factors of different units, such as from gallon to quart, from kilogram to pound, and from acre to hectare, please see Conversion Factors (http://edis.ifas.ufl.edu/ag126).

Take-home message

  1. Dry fertilizer and its active ingredients are both gravimetric—in other words, expressed as a weight per area.

  2. Liquid fertilizer and its active ingredients are expressed on a volumetric basis and expressed as a volume per area.

  3. The key point for the conversion from liquid to dry fertilizer is the density of the liquid fertilizer.

  4. The greater the density of a liquid fertilizer, the more active ingredient volume. However, the active ingredients of a liquid fertilizer are NOT linearly proportional to the fertilizer's density.

  5. To avoid any errors, the conversion calculation from liquid to dry fertilizer must include the liquid fertilizer's density and active ingredient content.

References

Burt, C. M., K. O'Connor, and T. A. Ruehr. 1995. Fertigation. San Luis Obispo: Irrigation Training & Research Center.

Olson, S. M., P. J. Dittmar, G. E. Vallad, S. E. Webb, S. A. Smith, E. J. McAvoy, B. M. Santos, and M. Ozores-Hampton. 2012. Potato Production in Florida. Gainesville: HS739. University of Florida Institute of Food and Agricultural Sciences. http://edis.ifas.ufl.edu/cv137.

Tables

Table 1. 

Calculations of liquid nitrogen fertilizer requirement for different fertigation scales and fertilizers with various fertilizer densities

Area fertigated

N requirement

Total N requirement

Fertilizer N content

Fertilizer requirement

Fertilizer density

Total fertilizer needed

(acre)

(lb/acre/event)

(lb/event)

(%)

(lb)

(lb/gal)

(gal/event)

Fertilizer: Dr. Earth® (3-3-3, fertilizer density: 10.51/gal)

1

2

2

3

66.7

10.51

6.3

2

2

4

3

133.3

10.51

12.7

3

2

6

3

200.0

10.51

19.0

4

2

8

3

266.7

10.51

25.4

5

2

10

3

333.3

10.51

31.7

6

2

12

3

400.0

10.51

38.1

7

2

14

3

466.7

10.51

44.4

8

2

16

3

533.3

10.51

50.7

9

2

18

3

600.0

10.51

57.1

10

2

20

3

666.7

10.51

63.4

Fertilizer: AgGrand® (4-3-3, fertilizer density: 9.01 lb/gal)

1

2

2

4

50.0

9.01

5.5

2

2

4

4

100.0

9.01

11.1

3

2

6

4

150.0

9.01

16.6

4

2

8

4

200.0

9.01

22.2

5

2

10

4

250.0

9.01

27.7

6

2

12

4

300.0

9.01

33.3

7

2

14

4

350.0

9.01

38.8

8

2

16

4

400.0

9.01

44.4

9

2

18

4

450.0

9.01

49.9

10

2

20

4

500.0

9.01

55.5

Table 2. 

Calculations of liquid phosphate fertilizer requirement for different fertigation scales and fertilizers with various fertilizer densities

Area fertigated

P requirement

Total P requirement

Fertilizer P content

Fertilizer requirement

Fertilizer density

Total fertilizer needed

(acre)

(lb/acre/event)

(lb/event)

(%)

(lb)

(lb/gal)

(gal/event)

Fertilizer: Dr. Earth® (3-3-3, fertilizer density: 10.51/gal)

1

2

2

3

66.7

10.51

6.3

2

2

4

3

133.3

10.51

12.7

3

2

6

3

200.0

10.51

19.0

4

2

8

3

266.7

10.51

25.4

5

2

10

3

333.3

10.51

31.7

6

2

12

3

400.0

10.51

38.1

7

2

14

3

466.7

10.51

44.4

8

2

16

3

533.3

10.51

50.7

9

2

18

3

600.0

10.51

57.1

10

2

20

3

666.7

10.51

63.4

Fertilizer: AgGrand® (4-3-3, fertilizer density: 9.01 lb/gal)

1

2

2

3

66.7

9.01

7.4

2

2

4

3

133.3

9.01

14.8

3

2

6

3

200.0

9.01

22.2

4

2

8

3

266.7

9.01

29.6

5

2

10

3

333.3

9.01

37.0

6

2

12

3

400.0

9.01

44.4

7

2

14

3

466.7

9.01

51.8

8

2

16

3

533.3

9.01

59.2

9

2

18

3

600.0

9.01

66.6

10

2

20

3

666.7

9.01

74.0

Footnotes

1.

This document is HS1200, one of a series of the Horticultural Sciences Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Original publication date April 2012. Visit the EDIS website at http://edis.ifas.ufl.edu.

2.

Guodong Liu, assistant professor, Horticultural Sciences Department; David Sui, Extension agent for commercial vegetable and tropical fruit, Palm Beach County; Gary K. England, multicounty Extension agent for fruit crops, Lake County, University of Florida, Insitute of Food and Agricultural Sciences, Gainesville, FL 32611

The use of trade names in this publication is solely for the purpose of providing specific information. UF/IFAS does not guarantee or warranty the products named, and references to them in this publication do not signify our approval to the exclusion of other products of suitable composition. All chemicals should be used in accordance with directions on the manufacturer's label.


The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other UF/IFAS Extension publications, contact your county's UF/IFAS Extension office.

U.S. Department of Agriculture, UF/IFAS Extension Service, University of Florida, IFAS, Florida A & M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, dean for UF/IFAS Extension.