Formulating an Organic Compost Recipe

Prepared by:
James C. Barker, Professor and Extension Specialist
Biological and Agricultural Engineering
North Carolina State University
Raleigh, NC

Published by: North Carolina Cooperative Extension Service

Publication Number: EBAE 173-93

Last Electronic Revision: March 1996 (JWM)

The following example formulates a poultry litter compost recipe from two ingredients (turkey grower house cake and and wheat straw) plus water. Typical moisture contents and carbon-to-nitrogen (C/N) ratios of various raw ingredients are given below:


                                  Moisture Content             C/N  
                                        %wb
__________________________________________________________________
Poultry carcass                          70                      5
Fresh manure, swine                      90                      6
            , poultry                    75                      6
            , cattle                     85                      8
Poultry house litter, cake               50                    7.5
                    , mixed              25                     10
                    , stockpiled         40                     15
Yard waste                               72                     14
Grass clippings                           -                     19
Horse stable manure                      50                     25
Legume grass hay                          -                     25
Potato tops                               -                     25
Fruit waste                               -                     35
Leaves                                    -                  40-80     
Peanut hulls                             10                     50
Cornstalks                               12                     60
Straw, oat                               10                     80
     , wheat                             10                    130
Bark                                      -                    100
Paper                                    20                    170
Sawdust                                  25                    500
Wood chips                                -                    700
Desired final compost mixture           50-60                20-30
__________________________________________________________________

To balance the C/N ratio, use these algebraic computations:


      Let:                         A     =    weight of litter
                               1 - A     =    weight of straw
                          A + (1 - A)    =    1

            A x 7.5  +  (1 - A) x 130    =    1 x 20
  
              7.5 A  +  130  -  130 A    =    20
   
                      7.5 A  -  130 A    =    20  -  130

                             -122.5 A    =   -110      which is the same as,
                              122.5 A    =    110
                                                           Parts by weight
                                                        ______________________
      litter:       A   =  110 / 122.5   =    0.90      0.90 / 0.90   =   1.00
      straw:    1 - A   =   1  -  0.90   =    0.10      0.10 / 0.90   =   0.11
                                             _____                       _____
                                              1.00                        1.11

To balance the moisture content, use these algebraic computations:


      Average moisture content of litter/straw mixture  = 

                     0.90  x  50%   +   0.10  x  10%    =    46 %

      Let:                         B     =    weight of litter/straw mixture
                               1 - B     =    weight of water needed
                          B + (1 - B)    =    1

             B x 46  +  (1 - B) x 100    =    1 x 50
 
               46 B  +  100  -  100 B    =    50

                       46 B  -  100 B    =    50  -  100
 
                                -54 B    =   -50      which is the same as,
                                 54 B    =    50
                                                          Parts by weight
                                                        ______________________
      litter/straw:      B  =   50 / 54  =    0.92      0.92 / 0.92   =   1.00
      water:         1 - B  =  1 - 0.90  =    0.08      0.08 / 0.92   =   0.08


Litter Compost Recipe:            Parts by              Pounds per 100 pounds
                                    weight                        compost mix	
                                  ________     ______________________________
      litter:     1.00  x  1.00   =   1.00     0.90  x  0.92  x  100   =   83
      straw:      0.11  x  1.00   =   0.11     0.10  x  0.92  x  100   =    9
                 _____                        -----
      water:      1.11  x  0.08   =   0.09     1.00  x  0.08  x  100   =    8

Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.

EBAE 173-93

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