Cattle Manure Enhances Methanogens Diversity and Methane Emissions Compared to Swine Manure under Rice Paddy

<div><p>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 <i>mcr</i>A gene copy numbers were significantly higher in cattle than swine manure. Diverse groups of methanogens which belong to <i>Methanomicrobiaceae</i> 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.</p></div

Relationships between CH₄ emission rate, DOC concentration (A) and <i>mcr</i>A gene copy number (B), and Shannon diversity index (C) in soils during rice cultivation.

<p>Relationships between CH₄ emission rate, DOC concentration (A) and <i>mcr</i>A gene copy number (B), and Shannon diversity index (C) in soils during rice cultivation.</p

Correlation between total CH₄ flux, soil properties and rice yield.

<p>*<i>p<0.05, **p<0.01</i> and <i>***p<0.001</i>.</p><p>Correlation between total CH₄ flux, soil properties and rice yield.</p

Correlation between total CH₄ flux, soil properties, rice plant growth and yield characteristics.

<p>Note: * and *** denote significant at 5 and 0.1% levels, respectively.</p><p>Correlation between total CH₄ flux, soil properties, rice plant growth and yield characteristics.</p

Changes in CH₄ emission rates with time (A) and total CH₄ fluxes (B) under different levels of BES application during rice cultivation.

<p>Error bar indicates standard deviation (n = 3; mean ± SD). Different letters indicate significant difference according to Tukey’s post-hoc test (<i>P</i><0.05).</p

Relationships between CH₄ emission rates, coenzyme M concentration (A) and <i>mcrA</i> gene copy number (B) during rice cultivation.

<p>Relationships between CH₄ emission rates, coenzyme M concentration (A) and <i>mcrA</i> gene copy number (B) during rice cultivation.</p

Analysis of methanogen community composition by <i>mcr</i>A based T-RFLP under different manure application during rice cultivation.

<p>The number indicated Shannon diversity index (<i>H</i>).</p

CH₄ flux per grain yield, soil and rice plant growth and yield characteristics with different levels of BES at harvest.

<p>Note: Values in the same row followed by same letters are not significantly different at p<0.05, ANOVA with Tukey’s post-hoc test for separation of means. Means ± SD from three replicates for each determination.</p><p>CH₄ flux per grain yield, soil and rice plant growth and yield characteristics with different levels of BES at harvest.</p

Enzyme activities in soil at varying cultivation stages of rice plant tested in paddy fields with different levels of BES application.

<p>Note: Values in the same column followed by same letters are not significantly different at p<0.05, ANOVA with Tukey’s post-hoc test for separation of means. Means ± SD from three replicates for each determination.</p><p>^aEnzyme unit is ng of CH₄-C g^-1 soil hr^-1</p><p>^bEnzyme unit is μg of TPF g^-1 soil hr^-1</p><p>Enzyme activities in soil at varying cultivation stages of rice plant tested in paddy fields with different levels of BES application.</p

Changes of coenzyme M concentrations (A) and <i>mcrA</i> gene copy number (B) in rice paddy soils under different levels of BES application during rice cultivation.

<p>Error bar indicates standard deviation (n = 3; mean ± SD). Different letters indicate significant difference according to the Tukey’s post-hoc test (<i>p</i><0.05).</p