Criticism of UvA nitrogen research incorrect, write UvA researchers in response
There was no substantial calculation error in UvA nitrogen research published a year ago. That is what UvA researchers wrote in a response to a critical article published last week.
There is no question of a substantial miscalculation, UvA researchers Emiel van Loon, Henrik Barmentlo and Albert Tietema wrote Friday afternoon in a response to the critical article that appeared last week on the independent newsplatform Foodlog. However, the researchers did speak of a “inaccurate choice of words”.
The response was directly addressed to Wouter de Heij, the chemical engineer who strongly criticised the nitrogen study on dairy farms published by the UvA researchers a year earlier. According to his calculations, the report’s main conclusion - that less than 10 per cent of nitrogen from a dairy farm precipitates within 500 metres of the barn - would no longer hold true.
De Heij studied Figure 6 of the study, a figure illustrating how 6640 kilograms of nitrogen from the stable spreads around the farm and ends up in higher air layers. He correctly noted that 6640 kilograms of nitrogen emission could never come from a barn with 170 dairy cows and 90 young cows. In fact, that is much lower, around 1,600 kilograms of nitrogen. De Heij took this further and formulated the “rough but plausible idea” that 36 per cent of the nitrogen emissions of a dairy farm ends up on the farmyard. A lot higher than the UvA researchers had calculated.
But that is not correct, according to the UvA researchers. In addition to nitrogen emissions from livestock, they also included emissions from storage, applied fertiliser and applied organic fertiliser. They also mention this in the report, but in Figure 6 it is indicated as “stable”. It would have been better to use the word “farm” there, and better explain it underneath the figure, they state. This leaves the calculation unchanged, the UvA researchers conclude.
The UvA study on nitrogen precipitation at dairy farms already caused a stir when it was published in September last year. For three years, the researchers worked on the study that would, for the first time, measure the “actual” nitrogen precipitation around a dairy farm. And thus should give a definitive answer to the RIVM’s calculation model - questioned by some. The main conclusion: only 9 per cent of the nitrogen released from dairy farming precipitates in a 500-metre radius around the farm. The rest ends up in higher air layers.
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