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Reducing Greenhouse Gas Emissions from Livestock and Soils |
The aim of this study was to evaluate the effect of combining alkali treatment of rice straw with non-protein nitrogen (NPN) from nitrate in reducing methane production in an in vitro incubation system. The treatments in a split-plot 2*6 arrangement with four replications were: alkali treated straw with NaOH (0; 1; 2; 3; 4%) plus lime (Ca(OH)2) (4; 3; 2; 1; 0%) or untreated straw, and as NPN source potassium nitrate or urea. All treatments had fresh cassava leaf as protein source. The quantity of substrate was 12g to which were added 240 ml rumen fluids (from slaughtered buffalo) and 960 ml of buffer solution. The incubation was for 24h with measurements of total gas production, methane percentage at intervals of 4; 8; 12; 16 and 24 hours and determination of residual unfermented substrate at the end.
The proportion of substrate fermented after 24h was increased by alkali treatment and tended to increase as lime replaced NaOH (Figure 1). Total gas production and methane percentage increased with incubation time and were reduced when nitrate replaced urea at all fermentation stages. After 24h, the methane production per unit of fermented substrate was less when nitrate replaced urea (Figure 2). It is concluded that lime can replace NaOH as a means of increasing the fermentability of rice straw and that methane production is decreased with potassium nitrate as NPN source.
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| Figure 1. Effect of alkali treatment and source of NPN on fermentability of the substrate of rice straw and cassava leaf meal | Figure 2. Effect of alkali treatment and proportion of lime (L) and NaOH (N) in the alkali medium on methane produced per unit substrate fermented with urea or nitrate as the source of NPN |