By: Saqib Mukhtar
The design of animal waste management systems and comprehensive nutrient management plans require sampling and analyses of specie-specific manure. Therefore, it is important to understand how to estimate annual manure production and its chemical, physical and thermal constituents from animal feeding operations (AFOs) in Texas.
Tables 1 and 2 contain information on manure production and characteristics. Remember that their data is for planning purposes only. These estimates do not replace the need for manure sampling and analyses.
This table shows data on the following:
- Average animal weight
- Number of days the animal is on feed
- Daily excretion of manure per animal and its total solids (TS) and volatile solids (VS), or organic matter that can be converted into combustible gases by microbial activity or by exposure to temperatures greater than 1,100 degrees Fahrenheit
- Moisture content and nutrient – nitrogen (N), phosphorus (P) and potassium (K) – value.
Since commercial fertilizer is sold as having different ratios of inorganic N, P (as phosphate or P2O5) and K (as potash or K2O), P and K equivalents of P2O5 and K2O in manure, respectively, are also included in this table.
Values of P to P2O5 and K to K2O have been converted by multiplication factors of 2.29 and 1.2, respectively.
It presents number of animals finished (removed from AFOs and marketed), such as chickens for meat (broilers), or raised (e.g., milk cows per year). is information is based upon the most recently available information from National Agricultural Statistics Service and other sources noted at the bottom of this table.
Using animal population information in this table and the data from Table 1, annual production of manure and mass of TS, VS, N, P, P2O5, K and K2O from various animal types has been estimated on an “as excreted” basis.
The last column in Table 2 presents estimates of the energy value of manure in British Thermal Units (BTUs) on a “dry and ash free basis.” is measurement represents the heat required to raise the temperature of 1 pound of water by 1 degree Fahrenheit.
Total energy or heating value of manure for each animal specie per year has been calculated by multiplying total pounds of VS for every animal type and poultry litter by 8,500 BTUs per pound of VS.
Extensive field research by Texas Agricultural Experiment Station and Texas Cooperative Extension (TCE) has shown that 8,500 BTU/lb is a good estimate of dry, ash free heating value of livestock and poultry manure. For comparison, 1 kilowatt hour (kWh; 1,000 Watts of electrical energy for 1 hour) is equal to 3,413 BTUs. One erm or 100 cubic feet of natural gas will equal approximately 100,000 BTUs.
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