Effects of plastic sheet covering on greenhouse gas emission from beef cattle manure during storage

Abstract: In order to assess the effects of plastic sheet covering on CH4, N2O and CO2 emissions during short-term storage of beef cattle manure, the greenhouse gas emission rate was investigated in autumn (September 7, 2013 - October 6, 2013, average air temperature was 22.87℃) by the static chamber - gas chromatography (GC) method. Meanwhile, ambient air temperatures and manure temperatures (10 cm below the surface) were measured every 5 minutes using automatic temperature recorder. On the first day, manure samples were collected from the Simmental beef cattle (18-19 months old, average weight of 500 kg), mixed, homogenized and divided into 6 replicate piles (the length, width and height of every pile were 100, 100 and 20 cm, respectively). Every pile had 2 sampling sites. The following two different treatments were included in this experiment: natural storage group (control group) and plastic sheet cover storage group (covering group), and every group included 3 replicate piles and a total of 6 sampling sites. The plastic sheet was translucent polyethylene. The gas was sampled between 09:00 and 10:00 a.m. and analyzed for CH4, N2O and CO2 on the same day by using GC. The process of sampling included following steps: during each measurement, using glass syringe of 50 mL, gas samples were sampled from each treatment after 0, 10, 20 and 30 minutes when the lid was closed, passed through the connected switch valve and then were transferred into 0.1 L aluminum foil bags for storage. After each measurement, lids would be removed to make the manure be exposed to natural condition. The result showed that the density and free water content of the manure of covering group were significantly higher than that of control group (P<0.01). But the dry matter content, ash content and total nitrogen content were significantly lower than that of control group (P<0.01). In addition, plastic sheet covering storage could reduce the N2O and CO2 emissions by 94.85% (P<0.01) and 88.85% (P<0.01), respectively. But the effects of plastic sheet covering on CH4 emissions were not consistent in different stages. The daily average CH4 emission rate of covering group was reduced by 43.37% (P<0.01) compared with that of control group in the early stage of storage (within 9 days). In the later stage of storage, the daily average CH4 emission rate of covering group was significantly higher than that of control group (P<0.01). Considering the synthesis of CH4, N2O and CO2 emission rates (CO2 equivalents), the daily average CO2 equivalent of covering group was lower than that of control group within the first 9 days (P<0.01), but the daily average CO2 equivalent of covering group was higher than that of control group at the whole storage period (P <0.05). It is concluded that covering plastic sheet should be used to reduce N2O and CO2 emissions during the first 30 days and CH4 emission at the earlier stage of fresh manure storage, i.e. within the first 9 days when the air temperature is from 17.23 to 30.35℃.