Value of Liquid Swine Manure as a Fertilizer for Corn Production

The Livestock and Urban Waste Research (LUW) Team has conducted several research studies evaluating solid-liquid separation of swine slurry, composting of the separated biosolids, the land application of unprocessed (raw) slurry, separated effluent, compost and traditional inorganic fertilizer, and the effects of land application of these soil amendments on soil characteristics and ground water. The information contained in this communication compares the cost and economic value of using inorganic fertilizer, raw slurry, and compost as a soil amendment for corn production based on actual costs and nutrient analyses.

A list of abbreviations used throughout this narrative and within the tables is shown as Table 1.
The N, P and K values for RS, C, POT, DAP and AA are provided in Table 2. The composition of RS and C reflect average analyzed values for the years 2006 and 2007. The data shown in Table 3 are the actual purchase prices paid for AA, DAP, and POT. The application costs provided are actual costs charged by commercial applicators for the Lexington, Illinois area.

The data of Table 4 reflect calculated application rates required to produce 180 bushels of shelled corn: acre assuming each bushel of shelled corn produced requires 1.33 pounds of N and 0.22 pounds of P. The base fertilizer rate, then, to produce 180 bushes of shelled corn: acre is 252 lb. of AA, 176 lb. of DAP and 200 lb POT. This fertilization rate does not result in any carry-over N or P. The application of RS assumes that 35 percent of the N in RS is available during year one, 18 percent is available during year two and nine percent is available during year 3. The same three availability estimates were assumed for compost application. Compost application is based on the dry matter content but cost analyses are based on the wet weight of compost assuming compost is 40 percent DM. Because the N in RS and C varies in its availability an average application rate for four years was calculated and used to estimate nutrient carry-over and cost. In actually, heavier RS or C application rates: acre are required in year one, decreased in years two and three then rise again for year four, repeating the cycle to infinity assuming the N and P concentrations of RS and C do not change over time. This cyclic pattern emphasizes why yearly analyses of RS and C for nutrient concentration are so important if the producer desires to balance nutrient application with nutrient use and nutrient carryover, while maximizing profits.

The data of Table 5 show the implications of applying RS and C for their N content alone.
Row 1 represents IF applied to equal N and P utilization, without regard to K. At the application rates shown in Table 4 and row one of Table 5, the amount of K supplied equals 120 pounds K. This represents a typical POT application rate for the soils at the ISU Farm-Lexington. When compost is applied to supply 100 percent of the corn's N requirement, P is over applied by 54 lbs. and K is over applied by 47.2 lbs. When RS is applied to supply 100 percent of the corn's N requirement, P is over applied by 139.4 lbs and K is over applied 49.7 lbs. As future regulation prevents over application of P, applying RS or C to supply 100 percent of the corn's N requirement will be illegal and could pose environmental P contamination problems. Therefore, the last two rows of Table 4 and Table 5 represent combining RS and IF to supply the same N, P and K as supplied in row one with IF alone. Accordingly, the amount of N supplied equals 239 lb, P supplied equals 39.6 lb. and K supplied equals 120 lb. These application rates result in no carry-over P, assuming a 180 bushel corn yield. The data of Table 6 tells the real story and reflects how the value of manure and compost can change based on the cost of inorganic fertilizer. The cost to fertilize one acre of corn for N, P, K rose $100.17 from $121.92 in 2006 to $222.09 in 2008. As the cost of AA, DAP and POT increases so does the relative, comparative value of the RS and C. Perhaps more importantly, applying RS and IF to meet, without exceeding, the requirements for N and P results in greater value per gallon for RS compared to applying RS as the sole N source. The down side to utilizing RS and IF in combination to meet the corn plants requirements for N, P and K is that 5.5 times more acres are required to land apply the RS, comparing RS application rates of 5,156g:ac to 934g:ac. These data suggest that RS and C both have more value supplying P and K requirements than as a sole supplier of N. Sometimes doing the right thing environmentally pays off economically as well.

Applying RS and IF in combination to satisfy the N, P, and K requirements is more efficacious than over applying RS to meet N requirements alone. When RS was applied to meet 100 percent of the N requirements at 2006 prices, RS had a calculated value of 1.36¢:g. When RS was combined with AA and POT to meet N and P requirements, the 2006 calculated value of RS rose 4.42¢;g. When RS was applied to meet 100 percent of the N requirements at 2008 prices, RS had a calculated value of 3.0¢:g. When RS was combined with AA and POT to meet N and P requirements, the 2008 calculated value of RS rose to 9.56¢:g. A similar trend was found for applying C and IF in combination.

Liquid swine manure has been an under-valued soil amendment for producing corn. Liquid swine manure has even greater value as part of a combination fertilizer application program.


C = compost
RS = raw slurry
DAP = Diammonium phosphate
AA = Anhydrous Ammonia
IF = Inorganic fertilizer
g = gallon
ac = acre
lb = pounds
T = Ton
DM = Dry matter
N = Nitrogen
P = Phosphorus
K = Potassium
POT = Potash



POT     60.0
AA 82.0    
DAP 18.0 46.0  
C 01.5 00.3 00.6
RS 01.0 00.53 00.46



2006   2008


Purchase Application   Purchase Application
AA $449:T $6.00:ac   $730:T $6.50:ac
DAP $332:T $2.50:ac   $715:T $5.00:ac
POTASH $250:T $2.50:ac   $506:T $5.00:ac
C ? $2.00:ac   ? $4.00:ac
RS ? 1.0¢:g:ac   ? 1.3¢:g:ac


252 lb. AA 176 lb. DAP 200 lb POT
C 15.6T DM or 39.0T wet wt basis    
RS 5156 g or 41,248 lb    
RS + IF 934 g or 7472 lb RS; 200 lb AA   143 lb POT
C + IF 6.6 T DM or 16.50 T wet wt. 50 lb AA 68 lb POT

Table 5. N and P SUPPLIED (lb:ac)

Yield N req N supp P req P supp P excess
Range + 180 239 239 39.6 039.6 0
IF 180 239 239 39.6 039.6 0
C 180 239 239 39.6 093.6 54
RS 180 239 239 39.6 179.0 139.4
RS + AA + POT 180 239 239 39.6 039.6 0
C + AA + POT 180 239 239 39.6 039.6 0

Table 6. FERTILIZER COST ($:ac)

2006   2008
Fertilizer purchase application purchase application
IF 110.92 11.00 205.59 016.50
C 119.92 02.00 218.09 004.00
RS 070.36a 51.56 155.06a 067.03
RS/IF 041.25 80.67b 089.27 132.72
C/IF 091.67 30.25c 171.14 050.95

aCorresponds to 1.36¢:g for 2006 and 3.00¢:g for 2008 which represents the maximum value of RS relative to the cost of IF:ac minus the cost of applying RS.
bReflects application cost for RS, AA + POT and purchase cost for AA + POT; value of RS = 4.42¢:g:2006 and 9.56¢:g:2008
cReflects application cost for C, AA + POT and purchase cost for AA + POT; value of C = $5.56:T:2006 and $10.37:Ton:2008

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