J. McEniry

Anaerobic methane production from five common grassland species at sequential stages of maturity

Since grass will likely be a dominant feedstock for on-farm anaerobic digestion in Northwest Europe, changes in the chemical composition of five common grass species with advancing harvest date in the primary growth were investigated and related to specific CH(4) yields. The increase in fibre components with advancing harvest date had a negative impact on the specific CH(4) yield (253 and 225 Nl CH(4) kg(-1) VS for 12 May and 7 July harvests, respectively), and this impact was similar across the five grass species. At common growth stages, only small differences in herbage digestibility was observed between the grass species and this was reflected in similar specific CH(4) yields; however, the 26% lower area-specific CH(4) yield of the cocksfoot variety (Dactylis glomerata L. var. Pizza) would make it the most expensive of the five grass species to produce and the least suitable for anaerobic digestion.

Yield and chemical composition of five common grassland species in response to nitrogen fertiliser application and phenological growth stage

Abstract The interaction of grassland management factors such as plant species, rate of nitrogen (N) fertiliser application and stage of maturity at harvest, will determine the optimal balance of herbage yield, nutritive quality and ensilability for ruminant nutrition and/or industrial applications. This study investigated the effects of N fertiliser input and harvest date on the yield and chemical composition of five common grass species, and made comparisons with red clover. Perennial ryegrass (PRG), Italian ryegrass (IRG), tall fescue, cocksfoot, timothy and red clover were grown under two inorganic N fertiliser inputs (0 kg N ha−1 and 125 kg N ha−1; except red clover) and harvested at five dates (fortnightly from 12 May to 7 July) in the primary growth. Regression analysis of these data allowed comparison of the yield and chemical composition of each grass species at common growth stages, without the confounding effects of variation in maturity between grass species at common harvest dates. Of the grass species investigated, timothy was most productive in terms of dry matter (DM) yield and thus has the potential to provide a cheaper feed per unit DM. However, the most digestible grass species was PRG, with timothy being the lowest, and this could impact on both animal and bioenergy production potential. The most suitable grass species for ensiling was IRG (particularly when grown without fertiliser N) due to its higher water soluble carbohydrate (WSC) concentration and lower buffering capacity (BC) compared to all other grass species. In comparison to the grasses receiving inorganic N fertiliser, red clover had a numerically lower DM yield, but a higher mean DM digestibility and crude protein concentration. The lower WSC concentration and higher BC of the red clover may result in a greater preservation challenge during ensiling.

Comparison of specific methane yield of perennial ryegrass prepared by thermal drying versus non-thermal drying in small-scale batch digestion tests.

Dried milled biomass samples are frequently utilised in small-scale batch digestion tests. However, herbage chemical composition can be altered by thermal drying, and this may affect specific methane (CH4) yields. Thus, the specific CH4 yield of herbage pre- and post-ensiling, prepared by two preparation methods were compared. Perennial ryegrass samples were either non-thermally dried (i.e. subject to cryogenic conditions, -196 °C) or thermally dried (40 °C), prior to milling. Specific CH4 yield was subsequently determined in a small-scale batch digestion test. Herbage pre-ensiling yielded 204 and 243 L CH4 kg(-1)VS(added) and herbage post-ensiling yielded 212 and 188 L CH4 kg(-1)VS(added) with non-thermal dried and thermal dried sample preparation methods, respectively. Due to opposing effects of thermal drying on CH4 yields of herbage either pre- or post-ensiling, it is not recommended to use thermal drying. Instead, it is recommended that non-thermal dried herbage samples are used in small-scale batch digestion tests.

Grass for Biogas Production—Anaerobic Methane Production from Five Common Grassland Species at Sequential Stages of Maturity

Grassland biomass represents the most significant feedstock resource in Ireland, accounting for approximately 91 % of the 4.3 million hectares of agricultural land. Grass can be an excellent energy crop and may be classified as a high yielding (up to 15 t dry matter ha− 1 a-1), low input perennial crop. Consequently, grass will be a dominant feedstock for anaerobic digestion (AD) on Irish farms. This study investigated the effects of stage of maturity of five grass species on methane production using dried, milled samples in a small-scale (160 ml), high-throughput batch digestion test. Five common grass species (perennial ryegrass, Italian ryegrass, cocksfoot, timothy and tall fescue) were grown in field plots (with three replicate blocks) under a high nitrogen fertiliser input (125 kg N ha− 1) and harvested at five sequential dates (fortnightly from 12 May to 7 July; n = 75 plots) in the primary growth. Of the five grass species investigated, average total CH4 production was highest (P 0.05).