Researchers question CBS ‘conclusions on ammonia

Researchers question the conclusions about ammonia in the 2019 study ‘Nitrogen loss from stored fertilizer’. This is compiled by Statistics Netherlands (CBS).

The methodology used by Statistics Netherlands to determine ammonia emissions from conventional and low emission stables is very sensitive to inaccuracies in the assumptions. Therefore, this method can not be used in litigation to draw conclusions about the operation of low-emission housing systems. This is the opinion of various (international) emission experts who have researched the CBS methodology on behalf of the I-VEE Foundation as a ‘review’.

Professor Sven Gjedde Sommer from Aarhus University in Denmark, Carin Rougoor and Frits van der Schans (both from CLM Research and Advice) note that there is great variation in sampling and analysis of nitrogen (N) and phosphate (P) in animals. fertilizer. Furthermore, there is a high degree of inaccuracy in the CBS calculations of the N and P secretions.

Air scrubbers and low emission floors

The review of the three researchers is relevant because in various lawsuits about nature permits for livestock farming, the function of techniques such as air scrubbers and low-emission floors is questioned on the basis of the CBS study.

The I-VEE Foundation notes that the CBS report has a strong inhibitory effect on the innovative power of livestock farming. Finding solutions to reduce emissions of ammonia and greenhouse gases is therefore at risk, the fund believes.

Slurry analysis number

‘It is doubtful whether the average of fertilizer analysis figures from a selection of houses guarantees the average of all houses in the relevant category’, states Sommer. Given these inaccuracies and variations, the nitrogen that cannot be attributed to one source in the CBS calculation should not only be considered as ammonia emissions from barns. The professor argues for a thorough statistical analysis of the CBS numbers. This should show if there is any residual nitrogen (N-residue) at all.

Rougoor and Van der Schans also conclude that intensive dairy and beef cattle farms are overrepresented in the CBS study. This is because fully land-based companies do not dispose of manure and therefore no manure samples are available. Extensive, non-manure removed farms will probably have more grass in the ration, and intensive fertilizer farms will have more corn. ‘Corn rations are therefore overrepresented in the CBS analysis.’

silage maize ration

According to CLM researchers, it affects the average ration for this group of animals and thus the nitrogen and phosphate excretion. A silage maize ration produces about 2 percent lower N: P2O5 ratios in the excretion of nitrogen and phosphate. The elimination figures for the group of intensive farms will probably differ even more, because these farms buy a larger share of the feed than the extensive farms, the researchers describe.

If the nitrogen excretion is 5 percent lower than assumed, or the phosphate excretion is 5 percent higher than assumed, then the N: P2O5 ratio in the cattle manure at the time of transport (average over all years and all barn types) corresponds to the calculated value, Rougoor and Van der Schans conclude. In that case, on average, there is no unexplained nitrogen component (N residue) for cattle manure.

Further research

‘The fact that the CBS analysis structurally provides a higher estimate of ammonia emissions than expected from national emission data, without it being possible to determine what causes this difference, indicates that further empirical research is needed,’ says Rougoor. According to her, a further sensitivity analysis provides a bandwidth and could therefore give a better picture of the results.

The I-VEE Foundation is an independent organization for research and knowledge dissemination. The fund mainly focuses on reducing ammonia emissions (NH3) and greenhouse gases – such as methane emissions (CH4) – from livestock sheds, manure storage and manure treatment and processing.

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