Lab-Scale Assessment of Gaseous Emissions from Laying-Hen Manure Storage as Affected by Physical and Environmental Factors

Abstract

Manure-belt (MB) and high-rise (HR) laying-hen houses are the two predominant housing types in the U.S. Compared with HR houses, MB houses have better indoor air quality and lower aerial emissions as a result of frequent (every 1 to 4 d) manure removal from the hen houses into separate manure storage. However, emissions from on-farm manure storage are integral parts of the whole-farm emissions and need to be quantified. This series of lab-scale studies assesses emission rates (ER) of ammonia (NH3) and greenhouse gases (CH4, CO2, and N2O) from stored laying-hen manure as affected by the following physical and environmental factors: air exchange rate (10 or 20 air changes per hour, or ACH), manure stacking configuration expressed as surface area to stack volume ratio (SVR at 2.5, 5, 10, or 20 m-1), air temperature (constant at 25C or diurnal cyclic from 21C to 32C), manure moisture content (MC, 50% or 77%), and periodic addition of new manure to the existing stack. Results of the studies showed the following: (1) air exchange rate of 10 or 20 ACH had no apparent effects on the gaseous emissions; (2) SVR significantly affected emissions, with larger SVR leading to higher NH3 and CO2 ERs but lower CH4 ER on per kg manure basis; (3) emissions were positively related to air temperature; and (4) laying-hen manure with 77% MC had higher emissions than that with 50% MC. At the storage condition of 25C air temperature, 20 ACH, every 2 d addition of 120 kg (5 cm thick layer) manure at 75% MC (equivalent to 2 d manure production of 682 laying hens) to the flat base area of 2.8 m2, the daily gaseous ERs per hen were 0.06 to 0.22 g NH3, 1.6 to 4.8 g CO2, and 7.4 to 32 mg CH4 (0.18 to 0.8 g CO2e). N2O concentrations from the stored manure were below the detection limit (0.03 ppm) of the measurement instrument; hence, N2O emission was omitted from the presentation.