Effect of frequent application of MgCl2 to slurry on ammonia emission from dairy barns (phase 2)

Magnesium chloride (MgCl2) is a salt produced by Nedmag B.V. is won in the Northern Netherlands. Applied in slurry, it can reduce the emission of ammonia from the manure through the binding of ammonium.

Research is being conducted at Dairy Campus into the application of MgCl2 in slurry. The aim of the project is to determine under practical conditions the effect of adding MgCl2 to manure on ammonia emissions from a dairy barn.

Excessive availability of nitrogen has adverse consequences for biodiversity in nature reserves. Ammonia emissions from livestock farming are a major source of this excess nitrogen and also represent a loss of an important agricultural mineral. When magnesium chloride (MgCl2) is added to animal manure, a reaction of magnesium, ammonium and phosphate occurs that leads to the formation of struvite. As a result, part of the ammonium is no longer available for ammonia emissions, but is not lost as fertilizer. Struvite is a fertilizer and due to its slow action, nitrogen and phosphate in particular are gradually released. The molar ratio between N:P:Mg in the average Dutch slurry is approximately 1:0.38:0.27. By increasing the Mg concentration, the total amount of nitrogen to be captured in slurry will therefore be a maximum of 38% of the total amount present due to the P limitation.

Previous experiments

In order to test this principle under practical conditions, the Ministry of Agriculture, Nature and Food Quality and Nedmag commissioned an experiment on Dairy Campus in 2021. Earlier research by Wageningen Environmental Research (laboratory) and MeetID (pot test) showed a significant reduction in NH3 emissions from manure that corresponded with the expected reduction.

The above findings had to be verified in a design and under conditions that are closer to practice. This happened in phase 1 at Dairy Campus at the end of 2021/beginning of 2022. The required amount of MgCl2 was administered in one go at the start of the measurements. However, this did not yield the expected results. No effect on ammonia emission was found with a single application at the start of the measurement period. Only in the last weeks of this period was any effect observed with daily administration of a MgCl2 solution over the grids. The reason for these disappointing results is probably that the effect of the MgCl2 is negated by the emission from the urine version of the floor and the top layer of the manure that is continuously added by the animals present. In phase 2, these findings will therefore be further elaborated in a new experiment. The facilities for determining emissions on the Dairy Campus also offer good opportunities for this. The MgCl2 is now not administered once but daily with a sprinkler system that was present on Dairy Campus. Farmin has adapted the developed dosing technique for this.

The aim

The aim of the project is to determine under practical conditions the effect of adding magnesium chloride (MgCl2) to manure on the ammonia emission from a dairy barn, whereby the following variables are varied: amount of MgCl2 with daily application, frequency of application and concentration of MgCl2.

The project is being carried out at Dairy Campus, Leeuwarden in two comparable departments for keeping dairy cattle that are equipped to measure ammonia emissions. The project will hopefully provide further insight into the possibilities of reducing ammonia emissions from dairy barns and a dose-response relationship through the daily use of MgCl2 in slurry. The design and results of the research conducted will be described in a public WLR report.

The results are expected in early 2023.