The loss of nitrogen (N) from animal manure can be determined in various ways. A recent study by Statistics Netherlands showed that there is a difference at national level between the losses calculated from the ammonia emissions and the losses calculated from the supply and removal of minerals. This difference was greatest for solid manure types and low-emission housing systems.
This issue also matters in other European countries. Commissioned by and in collaboration with the University of Aarhus, this study compares these two methods for determining nitrogen losses in a dairy farm. This research is part of the ECOMETA project funded by the Danish Innovation Fund.
What are we investigating?
Balance measurement vs emission measurement
The aim of the research is to compare two methods to determine the nitrogen losses
1. Balance measurements. The difference between all inputs and outputs is the loss of nitrogen. Phosphorus and Potassium are used as tracers.
2. Emission measurements. The losses occur in the form of emissions of ammonia and nitrous oxide. The loss can be determined by measuring this emission.
Why is this important?
Nitrogen losses from animal manure appear to be greater for some fertilizers based on the difference in the nitrogen-phosphate ratio during production by the animal and the discharge from the farm than on the basis of calculations via the NEMA model.
The difference is greatest with solid manure types and with low-emission housing systems. This is evident from a survey by Statistics Netherlands commissioned by the Experts Fertilizers Act (CDM). The most likely explanation for this difference in nitrogen loss is an underestimation of the emission factors for gaseous losses. With regular housing of cattle, pigs and poultry, the nitrogen loss based on the nitrogen / phosphate ratio comes close to the nitrogen loss calculated with emission factors.
When the nitrogen excretion rates are determined, the gaseous losses from the stable and manure storage are subtracted from the nitrogen excreted. The gaseous losses take the form of ammonia, nitrogen oxide, nitrous oxide and nitrogen gas.
Which activities do we carry out?
On 28th and 29th of April 2020, the manure pits in the two test sections were emptied and cleaned and the test started. We opted for a two-department design so that we can perform duplicate measurements. In each department, 16 lactating cows are housed. The investigation ends after about 12 weeks or as soon as the manure pits are full again. During the research, the intake and composition of roughage and concentrates and the milk production and composition are determined. At the end of the research period, the amount and composition of the manure produced is determined. Meanwhile, the emission of ammonia and nitrous oxide is continuously measured.
When do we expect results?
The measurement results are processed by the University of Aarhus. The results will be available early next year.