Abstract
Livestock manures are broadly used in agriculture to improve soil quality. However, manure application can increase the availability of organic carbon, thereby facilitating methane (CH4) production. Cattle and swine manures are expected to have different CH4 emission characteristics in rice paddy soil due to the inherent differences in composition as a result of contrasting diets and digestive physiology between the two livestock types. To compare the effect of ruminant and non-ruminant animal manure applications on CH4 emissions and methanogenic archaeal diversity during rice cultivation (June to September, 2009), fresh cattle and swine manures were applied into experimental pots at 0, 20 and 40 Mg fresh weight (FW) ha−1 in a greenhouse. Applications of manures significantly enhanced total CH4 emissions as compared to chemical fertilization, with cattle manure leading to higher emissions than swine manure. Total organic C contents in cattle (466 g kg−1) and swine (460 g kg−1) manures were of comparable results. Soil organic C (SOC) contents were also similar between the two manure treatments, but dissolved organic C (DOC) was significantly higher in cattle than swine manure. The mcrA gene copy numbers were significantly higher in cattle than swine manure. Diverse groups of methanogens which belong to Methanomicrobiaceae were detected only in cattle-manured but not in swine-manured soil. Methanogens were transferred from cattle manure to rice paddy soils through fresh excrement. In conclusion, cattle manure application can significantly increase CH4 emissions in rice paddy soil during cultivation, and its pretreatment to suppress methanogenic activity without decreasing rice productivity should be considered.
Highlights
Methanogens, the phylum Euryarchaeota within the domain of the Archaea, are important in global C cycle that mineralizes crop residues and soil organic matter under anaerobic conditions
These differences in CH4 emissions were more pronounced at 40 Mg ha21 cattle manure and swine manure than at other rates
The greater increase of labile organic C concentrations and plant available nutrients with cattle manure over swine manure enhanced methanogenic abundance in soil suggesting that ruminant methanogens of cattle manure is transferred to rice paddy soils as fresh excrement thereby stimulating more CH4 emissions during rice growth
Summary
Methanogens, the phylum Euryarchaeota within the domain of the Archaea, are important in global C cycle that mineralizes crop residues and soil organic matter under anaerobic conditions. Methanogens are found in a diverse range of habitats, for instance: wetlands, rice fields, fresh and marine water sediments, digestive tracts of ruminants and termites, anaerobic waste digesters, and geothermal vents [2] Among these habitats, flooded rice paddies are major contributors of CH4 to the atmosphere [3] and range between 39 to 112 Tg CH4 per year [4]. Manure addition can significantly increase CH4 emissions due to enhanced rice productivity and nutrient availability in the flooded paddy ecosystems [8, 9] Livestock manures, such as cattle and swine, may vary in their physicochemical and biological properties [10], which might have variable effect on microbial communities and CH4 emissions in rice paddy soils. CH4 emissions can be higher in rumen-derived methanogens from cattle-manured soils, there is no information in the literature comparing relative effects of different livestock manures from ruminant and non-ruminant animals on CH4 emission and methanogenic microbial communities in rice paddy soils
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