Formulating a Mortality 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-174-93

Last Electronic Revision: March 1996 (JWM)

The following example formulates a poultry mortality compost recipe from three ingredients (broiler carcass, house litter and wheat straw) plus water. Typical moisture contents and carbon - to - nitrogen (C/N) ratios of various raw ingredients are:


                                            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 and assumptions:


Let:

                             A    =   weight of carcass
                             B    =   weight of litter
                             C    =   weight of straw

Let:

                     A + B + C    =   1
                             B    =   1.5 A

i.e., by weight the recipe has 1.5 parts litter to 1 part carcass. For litter with higher C/N ratios, use 2 parts litter to 1 part carcass. How many parts straw are needed to balance the C/N ratio?


                                           C    =   1 - A - B
                                                =   1 - A - 1.5 A
                                                =   1 - 2.5 A

                A x 5  +  B x 10  +  C x 130    =   1 x 20

  A x 5  +  1.5 A x 10  +  (1 - 2.5 A) x 130    =   1 x 20

              5 A  +  15 A  +  130  -  325 A    =   20

                      5 A  +  15 A  -  325 A    =   20  -  130

                                      -305 A    =   -110  which is the same as
                                       305 A    =   110


                                                               Parts by weight
                                                       _______________________
    carcass:   A  =  110 / 305               =   0.36   0.36 / 0.36   =   1.00
    litter:    B  =  1.5 A  =  1.5 x 0.36    =   0.54   0.54 / 0.36   =   1.50
    straw:     C  =  1-A-B  =  1 -.36 -.54   =   0.10   0.10 / 0.36   =   0.27
                                                _____                    _____
                                                 1.00                     2.77

To balance the moisture content, use these algebraic computations:



            Average moisture content of solid ingredients  =

               0.36 x 70%  +  0.54 x 25%  +  0.10 x 10%    =   39.8 %

     Let:

                                  D    =   weight of solid ingredients
                              1 - D    =   weight of water needed
                        D + (1 - D)    =   1

         D x 39.8  +  (1 - D) x 100    =   1 x 50

           39.8 D  +  100  -  100 D    =   50

                   39.8 D  -  100 D    =   50  -  100

                            -60.2 D    =   -50      which is the same as
                             60.2 D    =   50


                                                              Parts by weight
                                                      _______________________
    solid ingred:       D   =   50 / 60.2   =   0.83   0.83 / 0.83   =   1.00
    water:          1 - D   =    1 - 0.83   =   0.17   0.17 / 0.83   =   0.20


Mortality                           Parts by            Pounds per 100 pounds
Compost Recipe:                       weight                      compost mix
                   _________________________   ______________________________
carcass:            1.00  x  1.00   =   1.00   0.36  x  0.83  x  100   =   30
litter:             1.50  x  1.00   =   1.50   0.54  x  0.83  x  100   =   45
straw:              0.27  x  1.00   =   0.40   0.10  x  0.83  x  100   =    8
                    _____                      _____
water:              2.77  x  0.20   =   0.57   1.00  x  0.17  x  100   =   17

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 174-93

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