Peter Sørensen vividly recalls the summers of his childhood, during which he often visited his grandparents' farm just north of Limfjorden. Although he grew up in the village Hals and did not have a farming background himself, he became fascinated by his grandparents' traditional homestead with 12 cows, pigs, chickens, and cultivated land. 

"It was hard manual labour, but it made sense," Peter Sørensen recalls, and fondly looks back on the summers in Northern Jutland. 

It was therefore not a big surprise that his interest in agriculture led him to work as a farm assistant for a year before deciding to continue his studies. 

"That year of practical work in the fields and the barn confirmed that I should study agronomy at what was then colloquially known as the Agricultural University, which is now part of the University of Copenhagen," he explains. 

Never thought he would become a researcher 

Peter Sørensen had never imagined that he would become a researcher after completing his agronomy education. However, fate led him to a Ph.D. position at Risø (now part of DTU – Technical University of Denmark), where he investigated livestock manure and nitrogen turnover in the soil. 

After his Ph.D., Peter Sørensen took a research position at Risø within the same field of research. Just 3 years later, he applied through the research council for a research project to continue working on nitrogen turnover in livestock manure, which brought him to Foulum (now part of Aarhus University Viborg). Here, he established himself as a researcher in livestock manure. 

Since Peter Sørensen joined Foulum and was employed there, his research area has expanded to encompass much more than nitrogen turnover and loss in livestock manure. Today, it also includes other nutrients such as phosphorus and sulphur, and the utilisation of ash, biochar, sludge, and especially biogas fertiliser. Furthermore, it has involved cover crops and their effects on both nitrate leaching and aftereffects. In addition, for many years, Peter Sørensen has been involved in the long-term organic crop rotation experiments at Foulumgaard, one of Aarhus University's experimental stations in crop production. 

"What interests me in these long-term experiments is, among other things, the interaction between different crops and, most importantly, the significance of cover crops for crop production, carbon sequestration in the soil, and nitrate leaching. It is also important for us to be able to make a direct comparison between organically and conventionally grown crops. I have always been interested in organic farming, but I hadn't worked with the subjet from a research perspective until I got involved in these long-term organic experiments," he says. 

A vision for sustainable agriculture 

Peter Sørensen's research has been driven not only by scientific curiosity but also by a deep understanding of the importance of sustainable resource utilisation in agriculture. He has used his expertise and will now also use his position as a professor to continue research in more sustainable production methods and resource-efficient solutions. His work within policy support has influenced the development of new legislations, policy guidelines and initiatives to promote sustainability in agriculture. He has authored a wide range of reports on the utilisation of livestock manure, nitrogen and climate measures, nitrate leaching, phosphorus limits, and much more. 

According to Peter Sørensen himself, there is a common thread throughout his career which is resource utilisation and recycling. 

"Today, circular bioeconomy is a widely discussed topic, which it wasn't as much when I started my research career. However, it has always been my desire that we should better utilise resources. So, it has been my focus, much like I have focused on the environment. Environment, resource utilisation, and recycling are closely interconnected," explains the newly appointed professor. 

N15 labelling of livestock manure 

Since his Ph.D. studies, Peter Sørensen has worked on developing methods that provide insight into how nitrogen moves through the agricultural system. An important tool for this purpose has been the use of N15-labelled livestock manure. 

Inspiring a future generation of researchers 

When teaching or supervising Master and Ph.D. students, Peter Sørensen is very conscious of inspiring and motivating. As he puts it, there needs to be someone to take over when he no longer will be spending his time on research. Therefore, he gladly supervises Ph.D. students and participates in projects that can further develop and guide younger researchers in their careers. 

"Currently, I am involved in an EU-funded project where Ph.D. students from all over Europe participate. From AU, Ph.D. student Jared Onyango Nyangau is part of the project. Together, we are working on biogas fertiliser and, more importantly, how to improve it," explains Peter Sørensen. And biogas fertiliser is precisely one of the things the new professor will focus on in the future. 

"There are still many challenges we need to try to solve. Especially concerning ammonia loss and low effect of biogas fertiliser. Biogas is otherwise a good climate measure because it converts energy from something that would otherwise become CO2—organic materials that would inevitably turn into CO2 at some point when they break down in the soil. At the same time, it can reduce emissions of another greenhouse gas, methane, which is released from manure if left untreated," says Peter Sørensen. 

Aarhus University has appointed Peter Sørensen as a professor in fertiliser, waste, and livestock manure management, effective from May 15, 2023. He will give his inaugural lecture during the fall of 2023, with more details will follow.