Maize silage for dairy cows: mitigation of methane emissions can be offset by land use change

Abstract

Increasing the digestibility of cattle rations by feeding grains and whole plant silages from maize have been identified as effective options to mitigate greenhouse gas emissions. The effect of ploughing grassland for maize crops have not been taken into account yet. A intensive dairy farm is used as an example to demonstrate the trade offs by this type of land use change when more maize silage is fed to dairy cows. The model DAIRY WISE has been used to calculate the mitigation by the changed ration, the Introductory Carbon Balance Model to calculate the changes in soil organic carbon and nitrogen caused by ploughing grassland for maize crops. The losses of soil carbon and the loss of sequestration potential are much larger than the annual mitigation by feeding more maize. The ecosystem carbon payback time defines the years of mitigation that are needed before the emissions due to land use change are compensated. For ploughing grassland on sandy soils, the carbon payback time is 60 years. A higher global warming potential for methane can reduce the carbon payback time with 30%. Ploughing clay soils with a higher equilibrium level of soil organic matter increases the payback time by maximally 70%. The payback times occur only in the case of permanent maize cropping, grass maize rotations cause annual losses of nitrous oxide that are larger than the mitigation by feeding more maize.

The influence of grass silage-to-maize silage ratio and concentrate composition on methane emissions, performance and milk composition of dairy cows

“…Rotz et al (2010) reported that, under a US production system, maize silage produces 5 kg CO 2 /tonne DM less than production of grass silage, which further enhances the potential environmental benefit of feeding maize silage over grass silage. In terms of the design of this study, assuming all other feed CO 2 emissions are the same and using the mean intakes, changing the grass-to-maize silage ratio from 70 : 30 to 30 : 70 would result in similar forage-related emissions of 428 g CO 2 /cow per day for M and 422 g CO 2 /cow day for G, despite the increased intake of cows offered M. However, Vellinga and Hoving (2011) have reported that converting land from permanent pasture to maize production for silage results in higher modelled greenhouse gas emissions than the trade-off from feeding a higher proportion of maize silage.…”

An LCA researcher's wish list – data and emission models needed to improve LCA studies of animal production

“…For example, soil structure should be incorporated in models, SOC content up to 1 m down should be modelled (most models only include top soils), and management factors, such as tillage, that influence crop residue and SOC depth distribution should be included (Stockmann et al, 2013). Vellinga and Hoving (2011) investigated the effect of dairy cattle feed by replacing pasture and grass silage with maize silage of high digestibility to reduce enteric CH 4 emissions. They modelled soil C changes when ploughing grassland for converting it into annual silage maize cropping to produce a feed with higher digestibility.…”

Whole-farm models to quantify greenhouse gas emissions and their potential use for linking climate change mitigation and adaptation in temperate grassland ruminant-based farming systems

“…These values were in the range (8%) observed by Dijkstra et al (2011) using a mechanistic model at the rumen level. However, where such a change in feeding strategy requires land use change from pasture to maize, soil C and N losses can be much greater than animal level emissions reductions (Vellinga and Hoving, 2011 Reducing CP may also alter the partition of N excreted resulting in a reduced ratio of urinary to dung N ), a subsequent reduction in the ratio of total ammonium N to organic N in the manure collected and possibly a reduction in associated NH 3 emissions. Manure VS, which are one of the main parameters to estimate the potential CH 4 emissions from manure storage, are expected to be reduced with lower CP in the diet.…”

“…Soil organic matter (SOM) dynamics and associated GHG emissions are also influenced by modifying the quality and composition of manure that is returned and more importantly, by changes in land use if animal diet changes (e.g. conversion of permanent grassland into maize (Vellinga and Hoving, 2011). Biogenic sources and sinks of CO 2 are often ignored in farm GHG models with the assumption that these do not contribute to changes in atmospheric CO 2 levels, that is, the source emissions equal that assimilated in sinks over the long term.…”

“…These values were in the range (8%) observed by Dijkstra et al (2011) using a mechanistic model at the rumen level. However, where such a change in feeding strategy requires land use change from pasture to maize, soil C and N losses can be much greater than animal level emissions reductions (Vellinga and Hoving, 2011).…”