Soil Respiration as Affected by Long-Term Broiler Litter Application to a Udult in the Ozark Highlands

The United States produced 8.4 billion broiler chickens (Gallus gallus) and an estimated 10.1 to 14.3 million Mg of broiler litter (BL) in 2012. Arkansas' production of 1 billion broilers in 2012 produced an estimated 1.2 to 1.7 million Mg of BL, most of which was concentrated in the Ozark Highlands region of northwest Arkansas. Increased CO2 release from soils associated with agricultural practices has generated concerns regarding the contribution of certain agricultural management practices to global warming. The objectives of this study were to evaluate the effects of long-term (>6 yr) BL application to a Udult on soil respiration and annual C emissions and to determine the predictability of soil respiration based on soil temperature and moisture in the Ozark Highlands region of northwest Arkansas. Soil respiration was measured routinely between May 2009 and May 2012 in response to annual BL application rates of 0, 5.6, and 11.2 Mg dry litter ha(-1) that began in 2003. Soil respiration varied (P < 0.01) with BL rate, measurement date, and year. Additions of BL stimulated respiration after application, and rainfall events after dry-soil conditions stimulated respiration in all years. Soil temperature at the 10-cm depth, 0- to 6-cm soil volumetric water content (VWC), and annual CO2-C emissions were unaffected (P > 0.05) by BL application rate but differed (P < 0.01) among study years. Multiple regression indicated that soil respiration could be reasonably predicted using 2-cm-depth soil temperature (T-2cm) and the product of T-2cm and VWC as predictors (R-2 = 0.52; P < 0.01). Results indicate that organic amendments, such as BL, can stimulate release of CO2 from the soil to the atmosphere, potentially negatively affecting atmospheric greenhouse gas concentrations; thus, there may be application rates above which the benefits of organic amendments may be diminished by adverse environmental effects. Improved BL management strategies are needed to lessen the loss of CO2 from BL-amended soils.