Effects of covering materials and sawdust covering depths on ammonia and greenhouse gase emissions from cattle manure during storage

Abstract: Livestock production is the important source of gaseous emissions (NH3 and greenhouse gases) from agriculture. Storage of animal manure is reported to be an important agricultural source of the environmentally harmful gases. Generally, ammonia and greenhouse gas emissions from stored animal manure can be affected by environmental factors (temperature and wind speed) and storage stacking configuration. Most studies have focused on the emission of ammonia and greenhouse gases from slurry during storage. However, information of gaseous emissions from solid manure stored is limited. Material covering is expected to be an effective method to reduce gaseous emissions from the stored manure. Thus, two experiments were set up to study gaseous emissions during storage of the solid cattle manure, and the effect of covering depth (1, 3 and 5 cm) and two different covering materials (sawdust and straw) on emissions of ammonia and greenhouse gases. Polyvinylchloride cylindrical (30 cm in diameter and 90 cm in height) static vessels were designed and built to measure ammonia and greenhouse gas emissions in the laboratory experiment. Fresh cattle manure was collected from practicing farm of Rongchang Campus of Southwest University in Chongqing. After fully mixed, manure was filled into 12 barrels (24.2 cm in diameter and 15 cm in height). Barrels were enveloped by static vessels while measuring gaseous emissions. The stacking process commenced on May 29, 2014, and was measured for 49 days. In Experiment 1, the emissions of NH3, CH4, N2O and CO2 from an uncovered and three sawdust-covering heaps of solid cattle manure were compared. Considering that the stacking of solid manure was only 10 cm height (about 4 kg), sawdust covering depths of 1, 3 and 5 cm were selected. In Experiment 2, the emissions of NH3, CH4, N2O and CO2 were quantified using solid cattle manure (about 10 kg, 25cm stacking height) covered with sawdust (2 cm depth, 250 g) and straw (6 cm depth, 250 g) by using the method of static chamber. In Experiment 1, sawdust covering decreased cumulative NH3 emissions by 15.28%-58.13% and cumulative CO2 emissions by 4.61%-13.14% from cattle manure compared with that uncovered (P<0.05). However, sawdust covering simultaneously increased cumulative N2O emissions by 6.57%-20.02% and cumulative CH4 emissions by 29.82%-36.84% (P<0.05). The emission of NH3, N2O and CO2 decreased and the emission of CH4 increased with the increasing of sawdust covering depth in three treatments of sawdust covering. Considering that the indirect global warming potential of NH3-N per kilogram was calculated on the basis of an emission of 0.01 kg N2O-N and global warming potential in 100-year scale for CH4 and N2O, cumulative greenhouse gas emissions (based on CO2) were 103.80, 108.61, 103.57 and 101.36 g/kg of manure weight for uncovered treatment, sawdust covering treatments with the covering depths of 1, 3, and 5 cm, respectively. Total greenhouse gas emissions showed a downward trend with the increasing of covering depth for covering treatments. In Experiment 2, both sawdust covering and straw covering reduced cumulative NH3 and CO2 emissions from solid cattle manure compared with that without covering during storage (P<0.05), but increased cumulative CH4 emission (P<0.05). Compared with uncovered treatment, sawdust covering increased cumulative N2O emission from solid cattle manure (P<0.05). However, straw covering decreased cumulative N2O emission (P<0.05). Compared with straw covering, sawdust covering decreased cumulative NH3 emission by 16.14% from solid cattle manure. Cumulative N2O emission from solid cattle manure increased significantly by using sawdust covering compared with straw covering (P<0.05), 33.39 mg/kg for sawdust covering and 22.30 mg/kg for straw covering, respectively. Cumulative CH4 emissions from solid cattle manure covered with straw was significantly higher than that from solid cattle manure covered with sawdust (P<0.05), 2.53 vs. 2.07 g/kg, respectively. However, cumulative CO2 emissions from solid cattle manure covered with straw was significantly lower than that from solid cattle manure covered with sawdust (P<0.05), 32.62 vs. 34.65 g/kg, respectively. Cumulative greenhouse gas emissions were 94.14, 101.51 and 109.46 g/kg of manure weight based on CO2 for uncovered, sawdust covering and straw covering, respectively. Compared with sawdust covering, straw covering increased significantly total greenhouse gas emissions from solid cattle manure. The results show that the treatments with thicker sawdust-covering (3 and 5 cm) have better effect of reduction emission for greenhouse gases.