Effect of Broiler Litter Stockpiling Methods on Nutrient Transformations and Ammonia and Greenhouse Gas Emissions

Abstract

The United States (US) is the largest producer and supplier of poultry products worldwide and produces 9.16 billion broilers annually. In the US, 41% of the broiler industry is located in the southeastern region, accounting for 20% of the broiler production. Annually, the US broiler industry produces 13-26 million metric tons of broiler litter (BL). Broiler litter serves as a popular row crop soil amendment as it is an excellent source of macro and micronutrients required for crop growth. A rising concern regarding the rapid expansion in the broiler industry is litter management and disposal. Broiler litter cleaned out from poultry houses is usually stored for a certain period of time before field application. Stockpiling of BL during the storage results in ammonia (NH3) and greenhouse gas emissions (GHG) such as nitrous oxide (N2O), carbon dioxide (CO2), and methane (CH4), which contribute to global warming and climate change. Additionally, improper storage practices can result in nutrient losses, which can deteriorate the quality of BL and also develop nutrient hotspots at the storage site. To effectively manage the generated BL and reduce the agronomic and environmental implications, it is important to understand the impact of storage conditions on the NH3, GHG emissions as well as nutrient transformations in BL. So, the objectives of this study were 1) To determine the macro and micronutrient losses from BL piles as well as to evaluate the associated changes in nutrient concentrations in the soil profile at storage site under three storage conditions (Tarp covered BL pile (treatment -T), Uncovered BL pile (treatment -U), soil covered BL pile (treatment -S)). 2) To quantify the NH3 and GHG emissions from the BL under three different storage conditions (Tarp-covered BL pile (treatment -T), Uncovered BL pile (treatment -U), soil-covered BL pile (treatment -S)). The study was conducted at E.V smith Research Station in Shorter, Alabama from September 2023- August 2024. Broiler 3 litter piles of 1.8m in height and 3.6m in width were constructed and replicated thrice. Treatments were allocated in a randomized complete block design. Nutrient concentrations were tracked for a period of 12 months from September 2023 - August 2024. Broiler litter samples were collected using a multipoint sampling approach and analyzed according to the standard methods of manure analysis. Changes in the soil profile nutrient status were tracked by collecting duplicate soil cores of 105cm deep from the base of each pile before and after the storage period. Gas concentrations were tracked for a period of 126 days (September 2023 – January 2024). Ammonia and GHG concentrations were measured simultaneously from two positions of the pile using a photoacoustic gas analyzer (INNOVA 1512). On each sampling day, gas measurements were recorded at 0, 1, 2, 3, 4, 5, 10, 15, 20, and 25-minute intervals. Additionally, moisture and temperature sensors were installed in the BL to track changes in moisture and temperature inside the BL piles, and a weather station to record the rainfall and ambient air temperature at the study site. Results showed that treatment - T showed lowest nutrient losses compared to treatments -U and -S. Over the 12 months of storage, treatment -T lost 36% TN, 23%TP, 17% TK, 17%TCa, 36% TMg, 29%TS, 10%TCu, 13%TZn. Whereas treatment -U lost 66% TN, 45% TP, 54% TK, 28%TCa, 44%TMg, 46%TS, 34%TCu, 42%TZn of initial concentration and treatment -S lost 59%TN, 41%TP, 40%TK, 33%TCa, 47%TMg, 45%TS, 38%TCu, 46%TZn of initial concentration. The results for nutrient changes in soil profile at storage site showed there was a significant increase in the soil nutrient concentrations (pH, TN, TC, Mehlich -1 (M1-P, M1-K, M1-Ca and M1-Mg)) after storage with the soil profile under treatment -U and -S showed increased concentrations into greater soil profile depth. After 12 months of storage treatment -U resulted in 3.4-9.2 fold increase in soil TN (60cm), 15 fold increase in soil M1-P (45cm), 1.4 -1.8 fold increase in soil M1-K (45cm), 1.3-1.5 fold increase in soil M1-Ca (45cm) and 1.7-1.2 fold increase in soil M1-Mg (45cm). Similarly, 4 treatment -S showed 3.6-7.3 fold increase in soil TN (60cm), 11.2 fold increase in soil M1-P (45cm), 1.6 fold increase in soil M1-K (45cm), 1.4-1.6 fold increase in soil M1-Ca (30cm) and 1.6-2.1 fold increase in soil M1-Mg (30cm) after 12 months of BL storage. Whereas for treatment -T the changes were not observed beyond 15 cm for all the soil nutrients. The results for impact of storage conditions on NH3 and GHG emissions showed that treatment-T significantly reduced the NH3 and GHG emissions over 126 days of the storage period compared to treatment-U and -S. During the 126-day storage period, treatment-T reduced NH3-N emissions by 38%, N2O-N emissions by 54%, CO2-C emissions by 28%, and CH4-C emissions by 19% compared to control (treatment-U). On the contrary, treatment-S promoted NH3-N emissions by 13%, N2O-N emissions by 17%, CO2-C emissions by 123%, and CH4-C emissions by 9% compared to control (treatment U). Overall, the Global warming potential for the three treatments was ranked as follows: S > U >T. Considering the agronomic and environmental implications, treatment-T was suggested as the best storage technique to mitigate the NH3 and GHG emissions and to preserve the nutrient quality of BL.