Effect of straw addition on nitrous oxide and methane emissions from stored farmyard manures

Stored solid manure heaps can be a significant source of nitrous oxide (N2O) and methane (CH4) emissions. The manure characteristics influence emissions and solid manure heaps can be managed to promote aerobic decomposition during storage. Increasing the carbon (C) content of the manure heap with high-C additives, such as straw, may provide the opportunity for N2O and CH4 emission reduction. Greenhouse gas (GHG) emissions from conventionally produced farmyard manure (FYM) have been quantified, but there is little data on emissions from organically produced FYM. NO and CH4 emissions were measured using a small-scale storage method from FYM collected from organic and conventional dairy units under a range of storage conditions with and without extra straw addition. The organic and the conventional FYM were similar in composition except for the higher C and dry matter content in the organic FYM and in the FYM with added straw. This resulted in mean total emissions of N2O and CH4 being lower from the organic (27 g N t(-1)) than the conventional FYM (52 g N t(-1)) and from the treatments with straw added (32 g N t(-1)) than those without (47 g N t(-1)). The initial C:N ratio and dry matter content of the stored FYM were the most important factors affecting N2O and CH4 emissions although the FYM temperature also affected CH4 emissions. Adding high-C additives, such as straw could be a promising strategy for reducing GHG emissions because it influences the dry matter content, C:N ratio and aeration of the manure. The small-scale FYM storage method were shown to be a reliable and an easy method to quantify emissions under a range of environmental conditions and manure manipulations and so develop effective manure management practices to reduce GHG emissions. (c) 2005 Elsevier B.V. All rights reserved.