Dutch farmer separates nitrogen from manure to fertilize crops

A Dutch farmer is making liquid fertilizer from cow manure so he can use the nutrients locally instead of moving them around the country.

Read Also

Europe’s manure mathematics frustrate farmers

Trucking manure is part of the strange nitrogen mathematics used in Europe as it attempts to balance nutrient use and penalizes manure based only on its nitrogen effect, without considering other nutrients, soil organic matter and biological benefits.

Ton Groot Roessink milks about 200 cows near Baak, using robots, automated feeding and automated manure cleaning. Manure from the farm is put through a biogas digester. The methane is burned to produce electricity and heat for the farm.

Those steps are standard for farms that use biogas digesters.

Groot Roessink is taking the process several steps further to make sure methane emissions are controlled and nutrients are added to crops in the most available form. He hopes his system can eventually be used across the Netherlands to manage manure.

Here’s how it works: Manure is moved to the biogas digester. He’s building a receiving pit so manure can be scraped in the barn each hour and quickly moved into the digester to reduce methane emissions.

The digestate is put through a screw press and solids are used for bedding or by neighbours who want it for gardens. Liquids are sent through another process.

The digester system produces lots of heat, which is collected in water that’s 80 or 90 C. It heats wash water and houses, but Groot Roessink looked for other ways to use it.

He uses the heat to warm liquid with nutrients from the digestate in a system of tubes that run back and forth and help produce ammonia. The liquid manure enters the system at about 17 C and exits at 60 to 70 C. “We try to make a lot of ammonia and we do it in a closed system.”

The ammonia is moved to a treatment system, where sulphuric acid and potassium nitrate are added. The solution is washed back through the system until it reaches eight per cent nitrogen.

The liquid fertilizer is stored in a silo and later used; either injected, applied with a sprayer or applied at the same time as the manure, depending on nitrogen content of the manure.

A new system is being installed that Groot Roessink expects will not require sulphuric acid and potassium nitrate to create liquid fertilizer.

“It’s a good system to make a circular concept for your farm and to minimize the emissions,” he says. “We have the practical research for five years and it was a good system, but now we want to test more things.”

He has funding from government agencies to help pay for the research.

Groot Roessink worked as a consultant on farmers’ manure plans before he returned to the farm. This gave him background to work on the problem at his family’s farm, which he runs with his girlfriend and parents.

Producing electricity from manure made more sense to him than making electricity from solar panels, which is popular on farms in the Netherlands.

“We have a lot of shit, but in the Netherlands, shit is a big problem,” he says. “It has a lot of positives when you can separate it.”

Why separate nitrogen from manure and then apply it with manure? It’s all about the rules, says Groot Roessink, as he uses his hand to mimic being choked higher on his neck as a metaphor for increasing regulations.

By pulling nitrogen out of the manure and bringing it back as a different product, it qualifies as a separate use of the nutrient.

Groot Roessink says he hopes his separation system will allow nutrients to be used closer to their source rather than trucked across the country, so it can benefit farmers in the Netherlands and around the world.