7.20     FERTILIZER

Fertilizer shall include the following information on the bag ticket or manufacturer's invoice:

n  net weight

n  name of the manufacturer and/or distributor       

n  guaranteed analysis of the fertilizer

 

These should be checked by the inspector in order to insure correct fertilizer grade and amount. "Fertilizer Grade" refers to the percentages of nitrogen (N), phosphoric acid (P2O5) and potassium (K2O) present. The contractor must furnish a list of the number of containers and a corresponding weight ticket from an approved scale for fertilizer used in the work.

 

            Fertilizer spilled on the ground shall be promptly cleaned up in accordance with Iowa Administrative Rule 21-44.57(4).

 

7.21     EXAMPLE CALCULATIONS -

           

A.    CHEMICALLY COMBINED FERTILIZER

 

Example No. 1

 

X-X-X fertilizer is specified, and contractor provides Y-Y-Y fertilizer.  Determine equivalent rate of Y-Y-Y fertilizer.

 

Specified:  500 pounds of 12‑12‑12 chemically combined commercial fertilizer per acre.  The contractor may furnish an equivalent grade such as 10‑10‑10, 13‑13‑13, 14‑14‑14, 15‑15‑15, 16‑16‑16, etc., chemically combined fertilizer.  The nutrients in the above grades of fertilizer are of the same ratio (1‑1‑1).

 

To calculate the pounds of 13‑13‑13 fertilizer needed to provide the plant nutrients specified for 500 lbs. of 12‑12‑12, divide the percent of the required analysis by the percent of the furnished analysis for the same nutrient.

 

500 lbs. per acre x 12% required = 500 (12) = 462 lbs. per acre

      13% furnished                                13

 

Therefore, 462 lbs. of 13‑13‑13 is equivalent to 500 lbs. of 12‑12‑12.

 

If hydro‑seeder is used, the contractor may furnish each nutrient as a separate material or use two or more chemically combined nutrients.

 

Example No. 2

 

X-X-X fertilizer is specified, and contractor provides three other types of fertilizer.  Contractor has also provided their proposed application rates.  Determine if the provided application rates are equivalent.

 

400 lbs. of 14‑14‑14 per acre is specified.  The contractor has furnished the following fertilizer grades and amounts:  140 lbs. of 30‑10‑0, 88 lbs. of 16‑48‑0, and 94 lbs. 0‑0‑60.  Determine if what the contractor has provided is equivalent.

 

1)     Compute the lbs. of each nutrient required per acre:

 

400 lbs. x 14% (N) = 56 lbs. N

400 lbs. x 14% (P2O5) = 56 lbs. P2O5

400 lbs. x 14% (K2O) = 56 lbs. K2O

 

2)   Compute the lbs. of each nutrient provided per acre:

 

N:  140 lbs. x 30% + 88 lbs. x 16% = 42 + 14.1 = 56.1 lbs.

P2O5:  140 lbs. x 10% + 88 lbs. x 48% = 14 + 42.2 = 56.2 lbs.

K2O:  94 lbs. x 60% = 56.4 lbs.

 

3)   Compare amounts provided in (2) to amounts required in (1)

 

N:  56.1 lbs. is greater than or equal to 56 lbs.

P2O5:  56.2 lbs. is greater than or equal to 56 lbs.

K2O:  56.4 lbs. is greater than or equal to 56 lbs.

 

So, the contractor has provided fertilizers that meet the required rates and they are equivalent.

 

Example No. 3

 

X-X-X fertilizer is specified, and contractor provides three other types of fertilizer.  Determine equivalent rates for the three other types.

 

Specified:  500 lbs. of 12‑12‑12 per acre.  The contractor may furnish the following fertilizer grades to meet the nutrient requirements:  30‑10‑0, 16‑48‑0, and 0‑0‑60.

 

1)   Compute the lbs. of each nutrient required per acre:

500 lbs. x 12% (N) = 60 lbs. N

500 lbs. x 12% (P2O5) = 60 lbs. P2O5

500 lbs. x 12% (K2O) = 60 lbs. K2O

 

2)   Compute the lbs. of 0‑0‑60 needed to furnish 60 lbs. of K2O:

60 lbs. K2O required =  60 = 100 lbs. of 0‑0‑60

60% furnished            0.60

 

                     OR

 

500 lbs. per acre x 12% required = 500 (12) = 100 lbs. of 0‑0‑60

      60% furnished                              60

 

3)   Compute the lbs. of 30‑10‑0 and the lbs. of 16‑48‑0 needed to furnish 60 lbs. of N and 60 lbs. of P2O5:

X = 30‑10‑0 component     Y = 16‑48‑0 component

 

a)   N = 0.30X + 0.16Y = 60

P2O5 = 0.10X + 0.48Y = 60

 

b)   Solve equations in (a) simultaneously

30 (0.30X) + 30 (0.16Y) = (30) (60)

9X + 4.8Y = 1800

 

c)   10 (0.10X) + 10 (0.48Y) = (10) (60)

1X + 4.8Y = 600

 

d)   Subtract equation (c) from equation (b) and solve for X.

  (9X + 4.8Y) = 1800

‑ (1X + 4.8Y) =  600

   8X              = 1200

     X              =   150 lbs.

 

e)   Substitute X into 1st equation in (a) and solve for Y.

0.30X + 0.16Y = 60

(0.30) (150) + 0.16Y = 60

45 + 0.16Y = 60

0.16Y = 60 ‑ 45

0.16Y = 15

Y = 93.7 (or 94 lbs.)

 

4)   150 lbs. of 30‑10‑0 per acre

 94 lbs. of 16‑48‑0 per acre

100 lbs. of 0‑0‑60 per acre

 

The above quantities supply the nutrient requirements per acre that are provided by 500 lbs. of 12‑12‑12.

 

 

B. COLD BLENDED FERTILIZER

Cold blended fertilizer is also allowed and can be a combination of different ingredients, such as:

·        Diammonium Phosphate (DAP) 18-46-0,

·        Monoammonium Phosphate (MAP) 11-52-0,

·        Muriate of Potash 0-0-60, and/or

·        Urea 46-0-0. 

 

Thus, one needs to understand: (1) what is required; (2) what is in these ingredients; and (3) how much of each ingredient is needed to meet the overall requirements. The following example problems will take you through calculations to help illustrate these concepts.

 

Additionally, a spreadsheet to determine or verify equivalent fertilizer rates is found on the Construction and Materials Bureau page:

https://iowadot.gov/Construction_Materials/earthwork_erosion/EquivalentWorksheet.xlsm

 

Example No. 1

 

The plan requires 100 pounds of 6-24-24 fertilizer per acre, but the fertilizer brought to the site is a cold mix with DAP (18-46-00) and Potash (0-0-60).  The ticket indicates that there are 52.2 pounds of DAP and 40 pounds of Potash for this cold blend.  Is this an equivalent amount of fertilizer for 1 acre?

 

1)     Check if there is an equivalent amount of nitrogen and phosphoric acid (P2O5) provided by the DAP (18-46-00):

 

Nitrogen:   100 lbs. x 6% required = 100 (6) = 33.3 lbs.

                      18% furnished                18

 

Phosphoric acid (P2O5):       100 lbs. x 24% required = 100 (24) = 52.2 lbs.

                                                    46% furnished                  46

 

Since both nitrogen and phosphoric acid are provided by DAP, the larger of the two amounts (which is 52.2 lbs.) must be used to provide at least an equivalent fertilizer amount.

 

The ticket indicated there is 52.2 pounds of DAP, so this provides an equivalent amount of nitrogen and phosphoric acid (P2O5).

 

2)     Check if there is an equivalent amount of potassium provided by the Potash (0-0-60):

 

Potassium (K2O):   100 lbs. x 24% required = 100 (24) = 40 lbs.

                                      60% furnished                60

 

The ticket indicated there is 40 pounds of Potash, so this provides an equivalent amount of potassium.

 

Therefore, 52.2 pounds of DAP and 40 pounds of Potash is an equivalent amount of fertilizer for 1 acre of 100 pounds of 6-24-24.

 

Example No. 2

 

Let’s change Example 1 so that the plan actually requires 500 pounds of 6-24-24 fertilizer per acre instead of 100 pounds per acre.  Since the required amount is now 500 pounds, the amounts of DAP and Potash, in this case, will have to be multiplied by a factor of 5 (500/100 = 5).  Thus:

 

For the required 100 pounds of 6-24-24 fertilizer per acre from Example 1, it is acceptable to have 52.2 pounds of DAP (18-46-0) and 40 pounds of Potash (0-0-60) cold-blend or total weight of 92.2 pounds.

 

For the required 500 pounds of 6-24-24 fertilizer per acre, the cold blend must have at least 261 pounds (52.2 x 5) of DAP and 200 pounds (40.0 x 5) of Potash or total weight of 461 pounds.

 

Or you could perform the calculations from Example 1, substituting 500 lbs. for 100 lbs.

 

Example No. 3

 

Example No. 2 shows the amounts of different ingredients for the cold blend fertilizer with DAP and Potash when the plan requires 500 pounds of 6-24-24 fertilizer per acre (261 pounds of DAP and 200 pounds of Potash).  The inspector should recognize that number of acres which are being seeded and calculate the total amount of fertilizer that should be spread.

 

For example:  The plan requires 500 pounds of 6-24-24 fertilizer per acre and there are 35 acres that will be seeded.  The contractor brings in the cold blend fertilizer with DAP and Potash.  From Example No. 2, the following calculations should be done:

 

DAP amount:  (261 pounds/acre) x 35 acres = 9,135 pounds of DAP

Potash amount:  (200 pounds/acre) x 35 acres = 7,000 pounds of Potash

 

The inspector can use the same calculation procedure to figure the amounts of different ingredients for the project(s).  The followings are some quick guidelines to check the amounts per acre.

 

For 500 pounds of 6-24-24 fertilizer per acre with a cold blend with MAP, Urea and Potash, the individual amounts are:

 

·        231 pounds of 11-52-0 MAP

·        10 pounds of 46-0-0 Urea

·        200 pounds of 0-0-60 Potash

 

For 500 pounds of 6-24-24 fertilizer per acre with a cold blend with DAP and Potash, the individual amounts are:

 

·        261 pounds of 18-46-0 DAP

·        200 pounds of 0-0-60 Potash

 

For 400 pounds of 6-24-24 fertilizer per acre with a cold blend with MAP, Urea and Potash, the individual amounts are:

 

·        185 pounds of 11-52-0 MAP

·         8 pounds of 46-0-0 Urea

·        160 pounds of 0-0-60 Potash

 

For 400 pounds of 6-24-24 fertilizer per acre with a cold blend with DAP and Potash, the individual amounts are:

 

·        209 pounds of 18-46-0 DAP

·        160 pounds of 0-0-60 Potash

 

For 300 pounds of 6-24-24 fertilizer per acre with a cold blend with MAP, Urea and Potash, the individual amounts are:

 

·        139 pounds of 11-52-0 MAP

·         6 pounds of 46-0-0 Urea

·        120 pounds of 0-0-60 Potash

 

For 300 pounds of 6-24-24 fertilizer per acre with a cold blend with DAP and Potash, the individual amounts are:

 

·        157 pounds of 18-46-0 DAP

·        120 pounds of 0-0-60 Potash

 

For 750 pounds of 13-13-13 fertilizer per acre with a cold blend with MAP, Urea and Potash, the individual amounts are:

 

·        188 pounds of 11-52-0 MAP

·        167 pounds of 46-0-0 Urea

·        163 pounds of 0-0-60 Potash

 

For 750 pounds of 13-13-13 fertilizer per acre with a cold blend with DAP, Urea and Potash, the individual amounts are:

 

·        212 pounds of 18-46-00 DAP

·        129 pounds of 46-0-0 Urea

·        163 pounds of 0-0-60 Potash

 

For 450 pounds of 13-13-13 fertilizer per acre with a cold blend with MAP, Urea and Potash, the individual amounts are:

 

·        113 pounds of 11-52-0 MAP

·        101 pounds of 46-0-0 Urea

·        98 pounds of 0-0-60 Potash

 

For 450 pounds of 13-13-13 fertilizer per acre with a cold blend with DAP, Urea and Potash, the individual amounts are:

 

·        128 pounds of 18-46-00 DAP

·        77 pounds of 46-0-0 Urea

·        98 pounds of 0-0-60 Potash

 

For 250 pounds of 13-13-13 fertilizer per acre with a cold blend with MAP, Urea and Potash, the individual amounts are:

 

·        63 pounds of 11-52-0 MAP

·        56 pounds of 46-0-0 Urea

·        55 pounds of 0-0-60 Potash

 

For 250 pounds of 13-13-13 fertilizer per acre with a cold blend with DAP, Urea and Potash, the individual amounts are:

 

·        71 pounds of 18-46-00 DAP

·        43 pounds of 46-0-0 Urea

·        55 pounds of 0-0-60 Potash

 

Again, the separate amounts are for one acre.  The inspector should multiply these amounts by the number of acres being seeded.

 

7.22     APPLICATION OF FERTILIZER

The fertilized area shall be disked and rolled with a cultipacker prior to seeding.  The project engineer may approve the substitution of a harrow if a cultipacker cannot be operated satisfactorily.